U.S. patent application number 16/254962 was filed with the patent office on 2020-07-23 for techniques for read operations.
The applicant listed for this patent is Micron Technology, Inc.. Invention is credited to Ferdinando Bedeschi, Umberto Di Vincenzo, Riccardo Muzzetto.
Application Number | 20200234761 16/254962 |
Document ID | / |
Family ID | 71608607 |
Filed Date | 2020-07-23 |
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United States Patent
Application |
20200234761 |
Kind Code |
A1 |
Bedeschi; Ferdinando ; et
al. |
July 23, 2020 |
TECHNIQUES FOR READ OPERATIONS
Abstract
Methods, systems, devices, and techniques for read operations
are described. In some examples, a memory device may include a
first transistor (e.g., memory node transistor) configured to
receive a precharge voltage at a first gate and output first
voltage based on a threshold of the first transistor to a reference
node via a first switch. The device may include a second transistor
(e.g., a reference node transistor) configured to receive a
precharge voltage and output a second voltage based on a threshold
of the second transistor to a memory node via a second switch. The
first voltage may be modified by a reference voltage and input to
the second transistor. The second voltage may be modified by a
voltage stored on a memory cell and input to the first transistor.
The first and second transistor may output third and fourth
voltages to be sampled to a latch.
Inventors: |
Bedeschi; Ferdinando;
(Biassono (MB), IT) ; Muzzetto; Riccardo; (Arcore
(MB), IT) ; Di Vincenzo; Umberto; (Capriate San
Gervasio (BG), IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Micron Technology, Inc. |
Boise |
ID |
US |
|
|
Family ID: |
71608607 |
Appl. No.: |
16/254962 |
Filed: |
January 23, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11C 13/004 20130101;
G11C 16/0483 20130101; G11C 2013/0054 20130101; G11C 16/28
20130101; G11C 7/1051 20130101 |
International
Class: |
G11C 13/00 20060101
G11C013/00; G11C 16/04 20060101 G11C016/04; G11C 16/28 20060101
G11C016/28; G11C 7/10 20060101 G11C007/10 |
Claims
1. An apparatus, comprising: a first transistor configured to
receive a first voltage at a first gate and output a second voltage
to a first node; a second transistor configured to receive a third
voltage at a second gate and output a fourth voltage to a second
node; a third transistor coupled with the first node and configured
to transmit the second voltage to a third node associated with a
memory cell, the second voltage being based at least in part on the
first voltage and a first voltage threshold of the first
transistor; a fourth transistor coupled with the third node and the
second gate of the second transistor and configured to selectively
bias the second gate based at least in part on the second voltage
and a logic state associated with the memory cell; and a latch
comprising a first input coupled with the first node and configured
to determine the logic state associated with the memory cell based
at least in part on receiving a reference voltage signal.
2. The apparatus of claim 1, further comprising: a fifth transistor
coupled with the second node and configured to transmit the fourth
voltage to a fourth node, the fourth voltage being based at least
in part on the third voltage and a second voltage threshold of the
second transistor; and a sixth transistor coupled with the fourth
node to the first gate of the first transistor and configured to
selectively bias the first gate based at least in part on the
fourth voltage.
3. The apparatus of claim 1, wherein the latch further comprises a
second input coupled with the second node and configured to
selectively receive a fifth voltage associated with the logic state
of the memory cell.
4. The apparatus of claim 1, wherein the first transistor and the
second transistor each comprise a source follower circuit.
5. A method, comprising: biasing a first gate of a first transistor
to a first voltage; precharging a first node to a second voltage
based at least in part on biasing the first gate of the first
transistor to the first voltage, the second voltage being based at
least in part on the first voltage and on a first threshold voltage
of the first transistor; coupling a memory cell with the first node
precharged to the second voltage based at least in part on
precharging the first node; biasing a second gate of a second
transistor to a third voltage based at least in part on coupling
the memory cell with the first node; and applying a fourth voltage
to a second node coupled with a latch and the second transistor
based at least in part on applying the third voltage to the second
gate of the second transistor, the fourth voltage being based at
least in part on the third voltage and a second threshold voltage
of the second transistor.
6. The method of claim 5, further comprising: determining a logic
state stored on the memory cell based at least in part on applying
the fourth voltage to the second node coupled with the latch.
7. The method of claim 5, further comprising: activating a third
transistor to couple the first transistor with the first node,
wherein precharging the first node is based at least in part on
activating the third transistor; and activating a fourth
transistor, after activating the third transistor, to couple the
first node with the second gate of the second transistor, wherein
biasing the second gate of the second transistor is based at least
in part on activating the fourth transistor.
8. The method of claim 5, wherein: the first transistor is
associated with a reference voltage supplied to the latch during a
read operation of the memory cell; and the second transistor is
associated with the fourth voltage indicating a logic state stored
in the memory cell and supplied to the second node of the latch
during the read operation of the memory cell.
9. The method of claim 5, further comprising: biasing the second
gate of the second transistor to the first voltage before biasing
the second gate to the third voltage; and precharging a third node
to a fifth voltage based at least in part on biasing the second
gate of the second transistor to the first voltage, wherein the
fifth voltage is based at least in part on the first voltage and on
the second threshold voltage of the second transistor.
10. The method of claim 9, further comprising, before applying the
forth voltage to the second node: applying a sixth voltage to a
first capacitor coupled with the first node after precharging the
first node, wherein the sixth voltage causes the third voltage
applied to the second gate of the second transistor to increase to
a seventh voltage; and applying an eighth voltage to a second
capacitor coupled with the third node after precharging the third
node, wherein the eighth voltage causes the fifth voltage applied
to the first gate of the first transistor to increase to a ninth
voltage.
11. The method of claim 10, further comprising: applying a tenth
voltage to a fourth node coupled with the latch, wherein the tenth
voltage is based at least in part on the ninth voltage and the
first threshold voltage of the first transistor; comparing the
fourth voltage applied to the second node coupled with the latch to
the tenth voltage applied to the fourth node coupled with the
latch; and determining a logic state stored on the memory cell
based at least in part on comparing the fourth voltage with the
tenth voltage, wherein the fourth voltage is based at least in part
on the seventh voltage and the second threshold voltage of the
second transistor.
12. The method of claim 9, further comprising: activating a fifth
transistor to couple the second transistor to the third node,
wherein precharging the third node is based at least in part on
activating the fifth transistor; and activating a sixth transistor,
subsequent to activating the fifth transistor, to couple the third
node to the first gate of the first transistor, wherein biasing the
first gate of the first transistor is based at least in part on
activating the sixth transistor.
13. The method of claim 5, wherein the first transistor and the
second transistor each comprise a source follower circuit.
14. A method, comprising: coupling a first node to a first voltage
source to increase the first node to a first voltage level as part
of a read operation of a memory cell; coupling a second node to a
second voltage source to increase the second node to a second
voltage level as part of the read operation of the memory cell;
applying a voltage increase to a first capacitor coupled with the
first node to increase a third voltage level of the first node
based at least in part on coupling the first node to the first
voltage source; coupling the first node with the second node based
at least in part on applying the voltage increase to the first
capacitor; and applying a reference voltage to a latch during the
read operation based at least in part on coupling the first node to
the second node.
15. The method of claim 14, further comprising: isolating the
second node from the second voltage source by deactivating a first
transistor before coupling the first node to the second node.
16. The method of claim 14, further comprising: coupling the second
node to a fourth voltage source by activating a second transistor
before coupling the first node to the second node.
17. The method of claim 14, further comprising: precharging a
second capacitor coupled with the second node based at least in
part on the third voltage level associated with a digit line
coupled with the first node.
18. The method of claim 14, further comprising: coupling, as part
of the read operation, a third node associated with the memory cell
to a third voltage source to increase the third voltage level of
the third node; and coupling the third node to a digit line to
increase a fourth voltage level of the digit line.
19. The method of claim 18, further comprising: applying the
voltage increase to a third capacitor coupled with the third node
based at least in part on coupling the third node to the digit
line.
20. The method of claim 19, further comprising: applying a fifth
voltage indicating a logic state stored on the memory cell to the
latch during the read operation based at least in part applying the
voltage increase to the first capacitor and the third
capacitor.
21. The method of claim 20, further comprising: determining the
logic state stored on the memory cell based at least in part on
comparing the fifth voltage to the reference voltage.
22. An apparatus, comprising: a first source follower coupled with
a reference voltage supply and configured to output a first signal
representative of a reference voltage provided by the reference
voltage supply; a second source follower coupled with a digit line
of a memory cell and configured to output a second signal
representative of a logic state stored by the memory cell; and a
reference capacitor coupled with the first source follower and
configured to modify a reference voltage offset associated with the
first signal.
23. The apparatus of claim 22, further comprising: a first
switching component coupled with the reference capacitor and a gate
of the first source follower, the first switching component
configured to establish a first conductive path between the
reference capacitor and the first source follower.
24. The apparatus of claim 23, further comprising: a second
switching component coupled with the reference capacitor and a
first voltage source, the second switching component configured to
establish a second conductive path between the first voltage source
and the reference capacitor.
25. The apparatus of claim 22, wherein the reference capacitor is
further configured to modify the reference voltage offset based at
least in part on a voltage level of the second signal that is
representative of the logic state stored by the memory cell.
Description
BACKGROUND
[0001] The following relates generally to a system that includes at
least one memory device and more specifically to techniques for
read operations that may include offset cancellation.
[0002] Memory devices are widely used to store information in
various electronic devices such as computers, wireless
communication devices, cameras, digital displays, and the like.
Information is stored by programming different states of a memory
device. For example, binary devices most often store one of two
states, often denoted by a logic 1 or a logic 0. In other devices,
more than two states may be stored. To access the stored
information, a component of the device may read, or sense, at least
one stored state in the memory device. To store information, a
component of the device may write, or program, the state in the
memory device.
[0003] Various types of memory devices exist, including magnetic
hard disks, random access memory (RAM), read only memory (ROM),
dynamic RAM (DRAM), synchronous dynamic RAM (SDRAM), ferroelectric
RAM (FeRAM), magnetic RAM (MRAM), resistive RAM (RRAM), flash
memory, phase change memory (PCM), and others. Memory devices may
be volatile or non-volatile. Non-volatile memory, e.g., FeRAM, may
maintain their stored logic state for extended periods of time even
in the absence of an external power source. Volatile memory
devices, e.g., DRAM, may lose their stored state when disconnected
from an external power source. FeRAM may be able to achieve
densities similar to volatile memory but may have non-volatile
properties due to the use of a ferroelectric capacitor as a storage
device.
[0004] Improving memory devices, generally, may include increasing
memory cell density, increasing read/write speeds, increasing
reliability, increasing data retention, reducing power consumption,
or reducing manufacturing costs, among other metrics. Some memory
cells may be configured to store multiple states. Improving an
efficiency (e.g., less power consumption, improved sensing
accuracy) of a sensing component of memory devices may also be
desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 illustrates an example of a system that supports
techniques for read operations in accordance with examples as
disclosed herein.
[0006] FIG. 2 illustrates an example of a memory die that supports
techniques for read operations in accordance with examples as
disclosed herein.
[0007] FIGS. 3A and 3B illustrate examples of hysteresis curves
that support techniques for read operations in accordance with
examples as disclosed herein.
[0008] FIG. 4 illustrates an example of a circuit that supports
techniques for read operations in accordance with examples as
disclosed herein.
[0009] FIG. 5 illustrates an example of a timing diagram that
supports techniques for read operations in accordance with examples
as disclosed herein.
[0010] FIGS. 6A-6C illustrates an example of a circuit that
supports techniques for read operations in accordance with examples
as disclosed herein.
[0011] FIG. 7 illustrates an example of a circuit that supports
techniques for read operations in accordance with examples as
disclosed herein.
[0012] FIG. 8 illustrates an example of a timing diagram that
supports techniques for read operations in accordance with examples
as disclosed herein.
[0013] FIG. 9 shows a block diagram of a memory device that
supports techniques for read operations and reference voltage
adjustment in accordance with aspects of the present
disclosure.
[0014] FIGS. 10 and 11 show flowcharts illustrating a method or
methods that support techniques for read operations in accordance
with examples as disclosed herein.
DETAILED DESCRIPTION
[0015] Memory devices use read operations to retrieve a data state
(e.g., logic 1 or logic 0) stored on a memory cell by transferring
a charge from the memory cell to a sense component. The data state
stored on the memory cell may be determined by comparing a memory
cell voltage to a reference voltage. The logic state stored on the
memory cell may be compared to the reference voltage to determine
the logic state stored on the memory cell. To improve sensing
accuracy, a sense component may include circuitry to amplify the
voltage response of the stored charge (e.g., as it is read from the
memory cell). Additionally, the circuitry may amplify and/or adjust
the level of the reference voltage to obtain an offset between the
voltage level associated with the first memory state and the
voltage level associated with the second memory state. For example,
it may be desirable to have the reference voltage between (e.g.,
half way between) a first memory state voltage and the second
memory state voltage.
[0016] In some cases, sense circuitry may include a transistor pair
that has a reference transistor isolated from a signal (e.g.,
memory side) transistor. Each of the transistors may be configured
as a source follower circuit where the output voltage may be
proportional to the voltage applied to the gate. In some cases, the
transistor pair may include a differential transistor pair.
Further, each transistor may have a different threshold voltage
that affects the voltage output of that transistor. Accordingly,
the charge stored on the memory device may be affected by the
memory side transistor threshold and the reference charge may be
affected a different amount by the reference side transistor
threshold. Thus, the final memory and reference voltages sampled by
the sense component may vary based on a threshold mismatch between
the different transistors, which may decrease the accuracy of a
sense process (e.g., increasing bit error rate).
[0017] Techniques for sensing a memory cell voltage using a
transistor pair with an offset cancellation component are
described. The sense operation may be carried out in multiple
phases where, during a first phase, each transistor in the
transistor pair may compensate for the voltage threshold of the
other transistor through charge sharing. For example, a precharge
voltage subjected to a reference transistor threshold drop may be
applied to the memory device side (e.g., memory node or signal
node). Similarly, a precharge voltage subjected to the memory
transistor threshold drop may be applied to the reference voltage
side (e.g., reference node). Thus, at the end of the first phase
the memory node may store a voltage that includes the threshold
effect from the reference transistor and the reference node may
store a voltage that includes a threshold effect from the signal
transistor.
[0018] In a second phase, the reference node voltage may be shifted
and amplified to achieve a reference voltage response at the sense
component that aids determination of the stored memory state. For
example, a reference node voltage may be offset from a memory
voltage signal associated with a first logic state and second logic
state. Likewise, the stored memory cell voltage can be applied to
the memory node and the memory node voltage can be amplified to
improve sensing accuracy.
[0019] In a third phase, the voltage on the reference node may be
transferred to a sense component via the reference transistor and
the voltage on the memory node may be transferred to the sense
component via the memory transistor. Thus, the reference voltage
may be offset by both the memory transistor threshold (e.g., from
phase 1 precharge) and the reference transistor threshold (e.g.,
phase 3 sampling to sense component). Similarly, the memory voltage
may be offset by both the reference transistor threshold (e.g.,
from phase 1 precharge) and the signal transistor threshold (e.g.,
phase 3 sampling to sense component). As a result, the voltage
mismatch between the transistor pair may be effectively removed
from the sampled reference and memory voltages. Removing
variability due to mismatched transistor thresholds may improve
sensing of the logic state stored by the memory cell.
[0020] Additionally or alternatively, memory device that include
amplification circuitry to amplify and offset the reference voltage
and amplify the memory voltage. In some cases amplification
circuitry may include independent circuits for each of the memory
side and reference side. That is, the memory device may have a
first amplification circuit for the reference node and a second
amplification circuit for the memory node. However, the circuitry
(e.g., capacitors) associated with each of the amplification
circuits may introduce one or more differences in voltage
responses, for example, due to different leakage rates from
electrical components (e.g., capacitors) in each of the circuits.
Thus, variability between the reference voltage and memory voltage
may result from such differences leading to increased variability
between the reference voltages and memory voltages, which may
reduce accuracy of a sense process.
[0021] Techniques for sensing a memory cell voltage using a coupled
amplification circuit are described. In some cases, the memory
amplification circuit and reference amplification circuit may be
coupled (e.g., short circuited) to produce the same voltage
response on each of the memory node and reference node. In some
cases, an additional capacitive circuit is added to the reference
node to mimic the voltage response of the memory node, for example
due to capacitive effects of the digit line. The capacitive circuit
may be initially coupled with a voltage source to charge the
capacitive node during a precharge period (e.g., first phase).
Before the amplification process the voltage source may be
disconnected from the capacitive node. Then, in conjunction with
the amplification procedure the capacitive node may be coupled to
the reference node to tune the voltage response of the reference
node to match the memory node, while having a consistent offset
between the first memory state (e.g., voltage level associated with
logic 1) and second memory state (e.g., voltage level associated
with logic 0). As a result, variability due to independent
amplification circuits may be decreased. In some cases, offset
cancellation and coupled amplification may be implemented to
improve the accuracy and/or reliability of a sense operation for a
memory device.
[0022] Features of the disclosure are initially described in the
context of a memory system and memory die as described with
reference to FIGS. 1-3. Features of the disclosure are described in
the context circuit diagrams, timing diagrams, and a diagram
illustrating operation of a circuit as described with reference to
FIGS. 4-8. These and other features of the disclosure are further
illustrated by and described with reference to an apparatus diagram
and flowcharts that relate to techniques for offset cancellation as
described with references to FIGS. 9-11.
[0023] FIG. 1 illustrates an example of a system 100 that utilizes
one or more memory devices in accordance with examples as disclosed
herein. The system 100 may include an external memory controller
105, a memory device 110, and a plurality of channels 115 coupling
the external memory controller 105 with the memory device 110. The
system 100 may include one or more memory devices, but for ease of
description the one or more memory devices may be described as a
single memory device 110.
[0024] The system 100 may include aspects of an electronic device,
such as a computing device, a mobile computing device, a wireless
device, or a graphics processing device. The system 100 may be an
example of a portable electronic device. The system 100 may be an
example of a computer, a laptop computer, a tablet computer, a
smartphone, a cellular phone, a wearable device, an
internet-connected device, or the like. The memory device 110 may
be component of the system configured to store data for one or more
other components of the system 100. In some examples, the system
100 is configured for bi-directional wireless communication with
other systems or devices using a base station or access point. In
some examples, the system 100 is capable of machine-type
communication (MTC), machine-to-machine (M2M) communication, or
device-to-device (D2D) communication.
[0025] At least portions of the system 100 may be examples of a
host device. Such a host device may be an example of a device that
uses memory to execute processes such as a computing device, a
mobile computing device, a wireless device, a graphics processing
device, a computer, a laptop computer, a tablet computer, a
smartphone, a cellular phone, a wearable device, an
internet-connected device, some other stationary or portable
electronic device, or the like. In some cases, the host device may
refer to the hardware, firmware, software, or a combination thereof
that implements the functions of the external memory controller
105. In some cases, the external memory controller 105 may be
referred to as a host or host device.
[0026] In some cases, a memory device 110 may be an independent
device or component that is configured to be in communication with
other components of the system 100 and provide physical memory
addresses/space to potentially be used or referenced by the system
100. In some examples, a memory device 110 may be configurable to
work with at least one or a plurality of different types of systems
100. Signaling between the components of the system 100 and the
memory device 110 may be operable to support modulation schemes to
modulate the signals, different pin designs for communicating the
signals, distinct packaging of the system 100 and the memory device
110, clock signaling and synchronization between the system 100 and
the memory device 110, timing conventions, and/or other
factors.
[0027] The memory device 110 may be configured to store data for
the components of the system 100. In some cases, the memory device
110 may act as a slave-type device to the system 100 (e.g.,
responding to and executing commands provided by the system 100
through the external memory controller 105). Such commands may
include an access command for an access operation, such as a write
command for a write operation, a read command for a read operation,
a refresh command for a refresh operation, or other commands. The
memory device 110 may include two or more memory dice 160 (e.g.,
memory chips) to support a desired or specified capacity for data
storage. The memory device 110 including two or more memory dice
may be referred to as a multi-die memory or package (also referred
to as multi-chip memory or package).
[0028] The system 100 may further include a processor 120, a basic
input/output system (BIOS) component 125, one or more peripheral
components 130, and an input/output (I/O) controller 135. The
components of system 100 may be in electronic communication with
one another using a bus 140.
[0029] The processor 120 may be configured to control at least
portions of the system 100. The processor 120 may be a
general-purpose processor, a digital signal processor (DSP), an
application-specific integrated circuit (ASIC), a
field-programmable gate array (FPGA) or other programmable logic
device, discrete gate or transistor logic, discrete hardware
components, or it may be a combination of these types of
components. In such cases, the processor 120 may be an example of a
central processing unit (CPU), a graphics processing unit (GPU), a
general purpose graphic processing unit (GPGPU), or a system on a
chip (SoC), among other examples.
[0030] The BIOS component 125 may be a software component that
includes a BIOS operated as firmware, which may initialize and run
various hardware components of the system 100. The BIOS component
125 may also manage data flow between the processor 120 and the
various components of the system 100, e.g., the peripheral
components 130, the I/O controller 135, etc. The BIOS component 125
may include a program or software stored in read-only memory (ROM),
flash memory, or any other non-volatile memory.
[0031] The peripheral component(s) 130 may be any input device or
output device, or an interface for such devices, that may be
integrated into or with the system 100. Examples may include disk
controllers, sound controller, graphics controller, Ethernet
controller, modem, universal serial bus (USB) controller, a serial
or parallel port, or peripheral card slots, such as peripheral
component interconnect (PCI) or specialized graphics ports. The
peripheral component(s) 130 may be other components understood by
those skilled in the art as peripherals.
[0032] The I/O controller 135 may manage data communication between
the processor 120 and the peripheral component(s) 130, input
devices 145, or output devices 150. The I/O controller 135 may
manage peripherals that are not integrated into or with the system
100. In some cases, the I/O controller 135 may represent a physical
connection or port to external peripheral components.
[0033] The input 145 may represent a device or signal external to
the system 100 that provides information, signals, or data to the
system 100 or its components. This may include a user interface or
interface with or between other devices. In some cases, the input
145 may be a peripheral that interfaces with system 100 via one or
more peripheral components 130 or may be managed by the I/O
controller 135.
[0034] The output 150 may represent a device or signal external to
the system 100 configured to receive an output from the system 100
or any of its components. Examples of the output 150 may include a
display, audio speakers, a printing device, or another processor on
printed circuit board, and so forth. In some cases, the output 150
may be a peripheral that interfaces with the system 100 via one or
more peripheral components 130 or may be managed by the I/O
controller 135.
[0035] The components of system 100 may be made up of
general-purpose or special purpose circuitry designed to carry out
their functions. This may include various circuit elements, for
example, conductive lines, transistors, capacitors, inductors,
resistors, amplifiers, or other active or passive elements,
configured to carry out the functions described herein.
[0036] The memory device 110 may include a device memory controller
155 and one or more memory dice 160. Each memory die 160 may
include a local memory controller 165 (e.g., local memory
controller 165-a, local memory controller 165-b, and/or local
memory controller 165-N) and a memory array 170 (e.g., memory array
170-a, memory array 170-b, and/or memory array 170-N). A memory
array 170 may be a collection (e.g., a grid) of memory cells, with
each memory cell being configured to store at least one bit of
digital data. Features of memory arrays 170 and/or memory cells are
described in more detail with reference to FIG. 2.
[0037] In some examples, the memory device 110 or the memory die
160 may be coupled with or include one or more amplification
components (e.g., to increase or decrease a voltage level), one or
more signal differentiation components, one or more sense
components or a combination thereof. Each memory cell of memory
array 170, for example, may be coupled with a digit line that may
be further coupled with a memory node. The memory node may be
coupled to a first input node of a latch via a first transistor
(e.g., source follower circuit). Each memory cell of memory array
170 may further be associated with a reference node. The reference
node may be coupled to a second input node of the latch via a
second transistor (e.g., a second source follower circuit). One or
more amplification circuits may be coupled to the memory node or
the reference node. For example, a first amplification circuit may
be coupled to the memory node and a second amplification generation
circuit may be coupled to the reference node. The first and second
amplification circuits may increase, decrease or shift a voltage
level at the memory or reference nodes to increase a memory voltage
from a memory cell or a reference voltage at the first and second
latch inputs.
[0038] The memory device 110 may be an example of a two-dimensional
(2D) array of memory cells or may be an example of a
three-dimensional (3D) array of memory cells. For example, a 2D
memory device may include a single memory die 160. A 3D memory
device may include two or more memory dice 160 (e.g., memory die
160-a, memory die 160-b, and/or any quantity of memory dice 160-N).
In a 3D memory device, a plurality of memory dice 160-N may be
stacked on top of one another or next to one another. In some
cases, memory dice 160-N in a 3D memory device may be referred to
as decks, levels, layers, or dies. A 3D memory device may include
any quantity of stacked memory dice 160-N (e.g., two high, three
high, four high, five high, six high, seven high, eight high). This
may increase the quantity of memory cells that may be positioned on
a substrate as compared with a single 2D memory device, which in
turn may reduce production costs or increase the performance of the
memory array, or both. In some 3D memory device, different decks
may share at least one common access line such that some decks may
share at least one of a word line, a digit line, and/or a plate
line.
[0039] The device memory controller 155 may include circuits or
components configured to control operation of the memory device
110. As such, the device memory controller 155 may include the
hardware, firmware, and software that enables the memory device 110
to perform commands and may be configured to receive, transmit, or
execute commands, data, or control information related to the
memory device 110. The device memory controller 155 may be
configured to communicate with the external memory controller 105,
the one or more memory dice 160, or the processor 120. In some
cases, the memory device 110 may receive data and/or commands from
the external memory controller 105. For example, the memory device
110 may receive a write command indicating that the memory device
110 is to store certain data on behalf of a component of the system
100 (e.g., the processor 120) or a read command indicating that the
memory device 110 is to provide certain data stored in a memory die
160 to a component of the system 100 (e.g., the processor 120). In
some cases, the device memory controller 155 may control operation
of the memory device 110 described herein in conjunction with the
local memory controller 165 of the memory die 160. Examples of the
components included in the device memory controller 155 and/or the
local memory controllers 165 may include receivers for demodulating
signals received from the external memory controller 105, decoders
for modulating and transmitting signals to the external memory
controller 105, logic, decoders, amplifiers, filters, or the
like.
[0040] The local memory controller 165 (e.g., local to a memory die
160) may be configured to control operations of the memory die 160.
Also, the local memory controller 165 may be configured to
communicate (e.g., receive and transmit data and/or commands) with
the device memory controller 155. The local memory controller 165
may support the device memory controller 155 to control operation
of the memory device 110 as described herein. In some cases, the
memory device 110 does not include the device memory controller
155, and the local memory controller 165 or the external memory
controller 105 may perform the various functions described herein.
As such, the local memory controller 165 may be configured to
communicate with the device memory controller 155, with other local
memory controllers 165, or directly with the external memory
controller 105 or the processor 120.
[0041] The external memory controller 105 may be configured to
enable communication of information, data, and/or commands between
components of the system 100 (e.g., the processor 120) and the
memory device 110. The external memory controller 105 may act as a
liaison between the components of the system 100 and the memory
device 110 so that the components of the system 100 may not need to
know the details of the memory device's operation. The components
of the system 100 may present requests to the external memory
controller 105 (e.g., read commands or write commands) that the
external memory controller 105 satisfies. The external memory
controller 105 may convert or translate communications exchanged
between the components of the system 100 and the memory device 110.
In some cases, the external memory controller 105 may include a
system clock that generates a common (source) system clock signal.
In some cases, the external memory controller 105 may include a
common data clock that generates a common (source) data clock
signal.
[0042] In some cases, the external memory controller 105 or other
component of the system 100, or its functions described herein, may
be implemented by the processor 120. For example, the external
memory controller 105 may be hardware, firmware, or software, or
some combination thereof implemented by the processor 120 or other
component of the system 100. While the external memory controller
105 is depicted as being external to the memory device 110, in some
cases, the external memory controller 105, or its functions
described herein, may be implemented by a memory device 110. For
example, the external memory controller 105 may be hardware,
firmware, or software, or some combination thereof implemented by
the device memory controller 155 or one or more local memory
controllers 165. In some cases, the external memory controller 105
may be distributed across the processor 120 and the memory device
110 such that portions of the external memory controller 105 are
implemented by the processor 120 and other portions are implemented
by a device memory controller 155 or a local memory controller 165.
Likewise, in some cases, one or more functions ascribed herein to
the device memory controller 155 or local memory controller 165 may
in some cases be performed by the external memory controller 105
(either separate from or as included in the processor 120).
[0043] The components of the system 100 may exchange information
with the memory device 110 using a plurality of channels 115. In
some examples, the channels 115 may enable communications between
the external memory controller 105 and the memory device 110. Each
channel 115 may include one or more signal paths or transmission
mediums (e.g., conductors) between terminals associated with the
components of system 100. For example, a channel 115 may include a
first terminal including one or more pins or pads at external
memory controller 105 and one or more pins or pads at the memory
device 110. A pin may be an example of a conductive input or output
point of a device of the system 100, and a pin may be configured to
act as part of a channel. In some cases, a pin or pad of a terminal
may be part of to a signal path of the channel 115. Additional
signal paths may be coupled with a terminal of a channel for
routing signals within a component of the system 100. For example,
the memory device 110 may include signal paths (e.g., signal paths
internal to the memory device 110 or its components, such as
internal to a memory die 160) that route a signal from a terminal
of a channel 115 to the various components of the memory device 110
(e.g., a device memory controller 155, memory dice 160, local
memory controllers 165, memory arrays 170).
[0044] Channels 115 (and associated signal paths and terminals) may
be dedicated to communicating specific types of information. In
some cases, a channel 115 may be an aggregated channel and thus may
include multiple individual channels. For example, a data channel
190 may be .times.4 (e.g., including four signal paths), .times.8
(e.g., including eight signal paths), .times.16 (including sixteen
signal paths), and so forth. Signals communicated over the channels
may use a double data rate (DDR) timing scheme. For example, some
symbols of a signal may be registered on a rising edge of a clock
signal and other symbols of the signal may be registered on a
falling edge of the clock signal. Signals communicated over
channels may use single data rate (SDR) signaling. For example, one
symbol of the signal may be registered for each clock cycle.
[0045] In some cases, the channels 115 may include one or more
command and address (CA) channels 186. The CA channels 186 may be
configured to communicate commands between the external memory
controller 105 and the memory device 110 including control
information associated with the commands (e.g., address
information). For example, the CA channel 186 may include a read
command with an address of the desired data. In some cases, the CA
channels 186 may be registered on a rising clock signal edge and/or
a falling clock signal edge. In some cases, a CA channel 186 may
include any quantity of signal paths to decode address and command
data (e.g., eight or nine signal paths).
[0046] In some cases, the channels 115 may include one or more
clock signal (CK) channels 188. The CK channels 188 may be
configured to communicate one or more common clock signals between
the external memory controller 105 and the memory device 110. Each
clock signal may be configured to oscillate between a high state
and a low state and coordinate the actions of the external memory
controller 105 and the memory device 110. In some cases, the clock
signal may be a differential output (e.g., a CK_t signal and a CK_c
signal) and the signal paths of the CK channels 188 may be
configured accordingly. In some cases, the clock signal may be
single ended. A CK channel 188 may include any quantity of signal
paths. In some cases, the clock signal CK (e.g., a CK_t signal and
a CK_c signal) may provide a timing reference for command and
addressing operations for the memory device 110, or other
system-wide operations for the memory device 110. The clock signal
CK may therefore may be variously referred to as a control clock
signal CK, a command clock signal CK, or a system clock signal CK.
The system clock signal CK may be generated by a system clock,
which may include one or more hardware components (e.g.,
oscillators, crystals, logic gates, transistors, or the like).
[0047] In some cases, the channels 115 may include one or more data
(DQ) channels 190. The data channels 190 may be configured to
communicate data and/or control information between the external
memory controller 105 and the memory device 110. For example, the
data channels 190 may communicate information (e.g.,
bi-directional) to be written to the memory device 110 or
information read from the memory device 110. The data channels 190
may communicate signals that may be modulated using a variety of
different modulation schemes (e.g., NRZ, PAM4).
[0048] In some cases, the channels 115 may include one or more
other channels 192 that may be dedicated to other purposes. These
other channels 192 may include any quantity of signal paths.
[0049] In some cases, the other channels 192 may include one or
more write clock signal (WCK) channels. While the `W` in WCK may
nominally stand for "write," a write clock signal WCK (e.g., a
WCK_t signal and a WCK_c signal) may provide a timing reference for
access operations generally for the memory device 110 (e.g., a
timing reference for both read and write operations). Accordingly,
the write clock signal WCK may also be referred to as a data clock
signal WCK. The WCK channels may be configured to communicate a
common data clock signal between the external memory controller 105
and the memory device 110. The data clock signal may be configured
to coordinate an access operation (e.g., a write operation or read
operation) of the external memory controller 105 and the memory
device 110. In some cases, the write clock signal may be a
differential output (e.g., a WCK_t signal and a WCK_c signal) and
the signal paths of the WCK channels may be configured accordingly.
A WCK channel may include any quantity of signal paths. The data
clock signal WCK may be generated by a data clock, which may
include one or more hardware components (e.g., oscillators,
crystals, logic gates, transistors, or the like).
[0050] In some cases, the other channels 192 may include one or
more error detection code (EDC) channels. The EDC channels may be
configured to communicate error detection signals, such as
checksums, to improve system reliability. An EDC channel may
include any quantity of signal paths.
[0051] The channels 115 may couple the external memory controller
105 with the memory device 110 using a variety of different
architectures. Examples of the various architectures may include a
bus, a point-to-point connection, a crossbar, a high-density
interposer such as a silicon interposer, or channels formed in an
organic substrate or some combination thereof. For example, in some
cases, the signal paths may at least partially include a
high-density interposer, such as a silicon interposer or a glass
interposer.
[0052] Signals communicated over the channels 115 may be modulated
using a variety of different modulation schemes. In some cases, a
binary-symbol (or binary-level) modulation scheme may be used to
modulate signals communicated between the external memory
controller 105 and the memory device 110. A binary-symbol
modulation scheme may be an example of a M-ary modulation scheme
where M is equal to two. Each symbol of a binary-symbol modulation
scheme may be configured to represent one bit of digital data
(e.g., a symbol may represent a logic 1 or a logic 0). Examples of
binary-symbol modulation schemes include, but are not limited to,
non-return-to-zero (NRZ), unipolar encoding, bipolar encoding,
Manchester encoding, pulse amplitude modulation (PAM) having two
symbols (e.g., PAM2), and/or others.
[0053] In some cases, a multi-symbol (or multi-level) modulation
scheme may be used to modulate signals communicated between the
external memory controller 105 and the memory device 110. A
multi-symbol modulation scheme may be an example of a M-ary
modulation scheme where M is greater than or equal to three. Each
symbol of a multi-symbol modulation scheme may be configured to
represent more than one bit of digital data (e.g., a symbol may
represent a logic 00, a logic 01, a logic 10, or a logic 11).
Examples of multi-symbol modulation schemes include, but are not
limited to, PAM4, PAM8, etc., quadrature amplitude modulation
(QAM), quadrature phase shift keying (QPSK), and/or others. A
multi-symbol signal or a PAM4 signal may be a signal that is
modulated using a modulation scheme that includes at least three
levels to encode more than one bit of information. Multi-symbol
modulation schemes and symbols may alternatively be referred to as
non-binary, multi-bit, or higher-order modulation schemes and
symbols.
[0054] In some cases, the external memory controller 105 or the
local memory controller 165 may control voltage increases (e.g., a
voltages boost) or voltage decreases (e.g., a voltage shift)
associated with a sense operation for one or more memory cells in
the memory arrays 170. For example, a first amplification circuit
may be coupled with a memory node of a sense circuit and a second
amplification circuit may be coupled with a reference node of the
sense circuit. During a read operation, a controller may cause the
first amplification circuit to increase (e.g., boost) a voltage on
the memory node. The controller may also cause the second
amplification circuit to decrease (e.g., shift) and increase (e.g.,
boost) a voltage on the reference node. Such boosting and shifting
operation may be performed during a read operation to develop a
reference voltage level that falls between a first logic state
(e.g., logic 1) and a second logic state (e.g., logic 0). In some
cases, the controller may cause one or more of the amplification
circuits to modify a voltage increase or decrease of the memory or
reference voltages during a read operation to improve sensing of
the logic state stored in the memory cell. For example, a reference
amplification circuit may apply a voltage decrease followed by a
voltage increase to a reference voltage that results in the
reference voltage level being approximately half way between the
voltage signal level associated with a first logic state (e.g.,
logic 1) and a second logic state (e.g., logic 0) stored on a
memory cell.
[0055] In some cases, one or more amplification circuits may be
coupled between the memory and reference nodes to produce the same
voltage response on each node. Further, the reference node may
include a capacitive circuit that can be operated to tune the
voltage response of the reference node to mimic the voltage
response of the memory node. In some, cases the capacitive circuit
may be coupled to a voltage source and ground element. In some
cases the capacitive circuit may be coupled the reference node via
a switch such that the capacitive circuit may be initially
decoupled from the reference node. The capacitive element may be
coupled to the reference node during a read operation to modify the
voltage level of the reference node before or in coordination with
sampling the reference voltage to a sense component.
[0056] FIG. 2 illustrates an example of a memory die 200 in
accordance with examples as disclosed herein. The memory die 200
may be an example of the memory dice 160 described with reference
to FIG. 1. In some cases, the memory die 200 may be referred to as
a memory chip, a memory device, or an electronic memory apparatus.
The memory die 200 may include one or more memory cells 205 that
are programmable to store different logic states. Each memory cell
205 may be programmable to store two or more states. For example,
the memory cell 205 may be configured to store one bit of digital
logic at a time (e.g., a logic 0 and a logic 1). In some cases, a
single memory cell 205 (e.g., a multi-level memory cell) may be
configured to store more than one bit of digit logic at a time
(e.g., a logic 00, logic 01, logic 10, or a logic 11).
[0057] A memory cell 205 may store a state (e.g., polarization
state or dielectric charge) that represents digital data. In FeRAM
architectures, the memory cell 205 may include a capacitor that
includes a ferroelectric material to store a charge and/or a
polarization representative of the programmable state. In DRAM
architectures, the memory cell 205 may include a capacitor that
includes a dielectric material to store a charge representative of
the programmable state.
[0058] Operations such as reading and writing may be performed on
memory cells 205 by activating or selecting access lines such as a
word line 210, a digit line 215, and/or a plate line 220. In some
cases, digit lines 215 may also be referred to as bit lines.
References to access lines, word lines, digit lines, plate lines or
their analogues, are interchangeable without loss of understanding
or operation. Activating or selecting a word line 210, a digit line
215, or a plate line 220 may include applying a voltage to the
respective line.
[0059] The memory die 200 may include the access lines (e.g., the
word lines 210, the digit lines 215, and the plate lines 220)
arranged in a grid-like pattern. Memory cells 205 may be positioned
at intersections of the word lines 210, the digit lines 215, and/or
the plate lines 220. By biasing a word line 210, a digit line 215,
and a plate line 220 (e.g., applying a voltage to the word line
210, digit line 215, or plate line 220), a single memory cell 205
may be accessed at their intersection.
[0060] Accessing the memory cells 205 may be controlled through a
row decoder 225, a column decoder 230, and a plate driver 235. For
example, a row decoder 225 may receive a row address from the local
memory controller 265 and activate a word line 210 based on the
received row address. A column decoder 230 receives a column
address from the local memory controller 265 and activates a digit
line 215 based on the received column address. A plate driver 235
may receive a plate address from the local memory controller 265
and activates a plate line 220 based on the received plate address.
For example, the memory die 200 may include multiple word lines
210, labeled WL_1 through WL_M, multiple digit lines 215, labeled
DL_1 through DL_N, and multiple plate lines, labeled PL_1 through
PL_P, where M, N, and P depend on the size of the memory array.
Thus, by activating a word line 210, a digit line 215, and a plate
line 220, e.g., WL_1, DL_3, and PL_1, the memory cell 205 at their
intersection may be accessed. The intersection of a word line 210
and a digit line 215, in either a two-dimensional or
three-dimensional configuration, may be referred to as an address
of a memory cell 205. In some cases, the intersection of a word
line 210, a digit line 215, and a plate line 220 may be referred to
as an address of the memory cell 205.
[0061] The memory cell 205 may include a logic storage component,
such as capacitor 240, and a switching component 245. The capacitor
240 may be an example of a ferroelectric capacitor. A first node of
the capacitor 240 may be coupled with the switching component 245
and a second node of the capacitor 240 may be coupled with a plate
line 220. The switching component 245 may be an example of a
transistor or any other type of switch device that selectively
establishes or de-establishes electronic communication between two
components.
[0062] Selecting or deselecting the memory cell 205 may be
accomplished by activating or deactivating the switching component
245. The capacitor 240 may be in electronic communication with the
digit line 215 using the switching component 245. For example, the
capacitor 240 may be isolated from digit line 215 when the
switching component 245 is deactivated, and the capacitor 240 may
be coupled with digit line 215 when the switching component 245 is
activated. In some cases, the switching component 245 is a
transistor and its operation is controlled by applying a voltage to
a transistor gate, where the voltage differential between the
transistor gate and transistor source is greater or less than a
threshold voltage of the transistor. In some cases, the switching
component 245 may be a p-type transistor or an n-type transistor.
The word line 210 may be in electronic communication with the gate
of the switching component 245 and may activate/deactivate the
switching component 245 based on a voltage being applied to word
line 210.
[0063] A word line 210 may be a conductive line in electronic
communication with a memory cell 205 that is used to perform access
operations on the memory cell 205. In some architectures, the word
line 210 may be in electronic communication with a gate of a
switching component 245 of a memory cell 205 and may be configured
to control the switching component 245 of the memory cell. In some
architectures, the word line 210 may be in electronic communication
with a node of the capacitor of the memory cell 205 and the memory
cell 205 may not include a switching component.
[0064] A digit line 215 may be a conductive line that connects the
memory cell 205 with a sense component 250. In some architectures,
the memory cell 205 may be selectively coupled with the digit line
215 during portions of an access operation. For example, the word
line 210 and the switching component 245 of the memory cell 205 may
be configured to selected couple and/or isolate the capacitor 240
of the memory cell 205 and the digit line 215. In some
architectures, the memory cell 205 may be in electronic
communication (e.g., constant) with the digit line 215.
[0065] A plate line 220 may be a conductive line in electronic
communication with a memory cell 205 that is used to perform access
operations on the memory cell 205. The plate line 220 may be in
electronic communication with a node (e.g., the cell bottom) of the
capacitor 240. The plate line 220 may be configured to cooperate
with the digit line 215 to bias the capacitor 240 during access
operation of the memory cell 205.
[0066] The sense component 250 may be configured to detect a state
(e.g., a polarization state or a charge) stored on the capacitor
240 of the memory cell 205 and determine a logic state of the
memory cell 205 based on the detected state. The charge stored by a
memory cell 205 may be extremely small, in some cases. As such, the
sense component 250 may include one or more sense amplifiers to
amplify the signal output of the memory cell 205. The sense
amplifiers may detect minute changes in the charge of a digit line
215 during a read operation and may produce signals corresponding
to either a logic 0 or a logic 1 based on the detected charge.
During a read operation, the capacitor 240 of memory cell 205 may
output a signal (e.g., discharge a charge) to its corresponding
digit line 215. The signal may cause a voltage of the digit line
215 to change. The sense component 250 may be configured to compare
the signal received from the memory cell 205 across the digit line
215 to a reference signal 255 (e.g., a reference voltage). The
sense component 250 may determine the stored state of the memory
cell 205 based on the comparison. For example, in binary-signaling,
if digit line 215 has a higher voltage than the reference signal
255, the sense component 250 may determine that the stored state of
memory cell 205 is a logic 1, and, if the digit line 215 has a
lower voltage than the reference signal 255, the sense component
250 may determine that the stored state of the memory cell 205 is a
logic 0. The sense component 250 may include various transistors or
amplifiers to detect and amplify a difference in the signals. The
detected logic state of memory cell 205 may be output through
column decoder 230 as output 260. In some cases, the sense
component 250 may be part of another component (e.g., a column
decoder 230, row decoder 225). In some cases, the sense component
250 may be in electronic communication with the row decoder 225,
the column decoder 230, and/or the plate driver 235.
[0067] In some examples, the sense component 250 may include, or
may be coupled with, a differential circuit coupled to one or more
memory cells 205 and reference signal 255 input. The differential
circuit may include a memory node coupled to one or more digit
lines 215 and a reference node coupled to the reference signal
input. The memory node may be coupled to a first transistor (e.g.,
first source follower circuit) and a first amplification circuit.
The reference node may be coupled to a second transistor (e.g.,
second source follower circuit) and a second amplification circuit.
In some cases, the first source follower may couple the signal node
to a first input of a latch and the second source follower may
couple the reference node to a second input of the latch. A voltage
signal read from a memory cell 205 to the memory node may be
modified (e.g., increases or decreased) by the first amplification
circuit before being applied to the first input of the latch. In
some cases, a reference voltage of the reference voltage signal 255
may be modified by a second amplification circuit before being
applied to the second input of the latch. The voltage signal and
reference voltage may be applied to the latch via activating the
first and second source follower circuits. In general, the latch
may compare a voltage level of the signal with the reference
voltage and output a signal based on a logic state stored at a
memory cell 205.
[0068] The local memory controller 265 may control the operation of
memory cells 205 through the various components (e.g., row decoder
225, column decoder 230, plate driver 235, and sense component
250). The local memory controller 265 may be an example of the
local memory controller 165 described with reference to FIG. 1. In
some cases, one or more of the row decoder 225, column decoder 230,
and plate driver 235, and sense component 250 may be co-located
with the local memory controller 265. The local memory controller
265 may be configured to receive one or more commands and/or data
from an external memory controller 105 (or a device memory
controller 155 described with reference to FIG. 1), translate the
commands and/or data into information that can be used by the
memory die 200, perform one or more operations on the memory die
200, and communicate data from the memory die 200 to the external
memory controller 105 (or the device memory controller 155) in
response to performing the one or more operations. The local memory
controller 265 may generate row, column, and/or plate line address
signals to activate the target word line 210, the target digit line
215, and the target plate line 220. The local memory controller 265
may also generate and control various voltages or currents used
during the operation of the memory die 200. In general, the
amplitude, shape, or duration of an applied voltage or current
discussed herein may be adjusted or varied and may be different for
the various operations discussed in operating the memory die
200.
[0069] In some cases, the local memory controller 265 may be
configured to perform a precharge operation on the memory die 200.
A precharge operation may comprise precharging one or more
components and/or access lines of the memory die 200 to one or more
predetermined voltage levels. In some instances, the memory cell
205 and/or portions of the memory die 200 may be precharged between
different access operations. In some instances, the digit line 215
and/or other components may be precharged before a read
operation.
[0070] In some cases, the local memory controller 265 may be
configured to perform a write operation (e.g., a programming
operation) on one or more memory cells 205 of the memory die 200.
During a write operation, a memory cell 205 of the memory die 200
may be programmed to store a desired logic state. In some cases, a
plurality of memory cells 205 may be programmed during a single
write operation. The local memory controller 265 may identify a
target memory cell 205 on which to perform the write operation. The
local memory controller 265 may identify a target word line 210, a
target digit line 215, and/or a target plate line 220 in electronic
communication with the target memory cell 205 (e.g., the address of
the target memory cell 205). The local memory controller 265 may
activate the target word line 210, the target digit line 215,
and/or the target plate line 220 (e.g., applying a voltage to the
word line 210, digit line 215, or the plate line 220), to access
the target memory cell 205. The local memory controller 265 may
apply a specific signal (e.g., voltage) to the digit line 215 and a
specific signal (e.g., voltage) to the plate line 220 during the
write operation to store a specific state in the capacitor 240 of
the memory cell 205, the specific state being indicative of a
desired logic state.
[0071] In some cases, the local memory controller 265 may be
configured to perform a read operation (e.g., a sense operation) on
one or more memory cells 205 of the memory die 200. During a read
operation, the logic state stored in a memory cell 205 of the
memory die 200 may be determined. In some cases, a plurality of
memory cells 205 may be sensed during a single read operation. The
local memory controller 265 may identify a target memory cell 205
on which to perform the read operation. The local memory controller
265 may identify a target word line 210, a target digit line 215,
and/or a target plate line 220 in electronic communication with the
target memory cell 205 (e.g., the address of the target memory cell
205). The local memory controller 265 may activate the target word
line 210, the target digit line 215, and/or a target plate line 220
(e.g., applying a voltage to the word line 210, the digit line 215,
or the plate line 220), to access the target memory cell 205. The
target memory cell 205 may transfer a signal to the sense component
250 in response to biasing the access lines. The sense component
250 may amplify the signal. The local memory controller 265 may
fire the sense component 250 (e.g., latch the sense component) and
thereby compare the signal received from the memory cell 205 to the
reference signal 255. Based on that comparison, the sense component
250 may determine a logic state that is stored on the memory cell
205. The local memory controller 265 may communicate the logic
state stored on the memory cell 205 to the external memory
controller 105 (or the device memory controller) as part of the
read operation.
[0072] In some memory architectures, accessing the memory cell 205
may degrade or destroy the logic state stored in a memory cell 205.
For example, a read operation performed on a ferroelectric memory
cell may destroy the logic state stored in the ferroelectric
capacitor. In another example, a read operation performed in DRAM
architectures may partially or completely discharge the capacitor
of the target memory cell. The local memory controller 265 may
perform a re-write operation or a refresh operation to return the
memory cell to its original logic state. The local memory
controller 265 may re-write the logic state to the target memory
cell after a read operation. In some cases, the re-write operation
may be considered part of the read operation. Additionally,
activating a single access line, such as a word line 210, may
disturb the state stored in some memory cells in electronic
communication with that access line. Thus, a re-write operation or
refresh operation may be performed on one or more memory cells that
may not have been accessed.
[0073] FIGS. 3A and 3B illustrate examples of non-linear electrical
properties of a ferroelectric memory cell with hysteresis curves
300-a and 300-b in accordance with various examples as disclosed
herein. Hysteresis curves 300-a and 300-b illustrate an example
ferroelectric memory cell writing and reading process,
respectively. Hysteresis curves 300-a and 300-b depict the charge,
Q, stored on a ferroelectric capacitor (e.g., capacitor 240
described with reference to FIG. 2) as a function of a voltage
difference, V.
[0074] A ferroelectric material is characterized by a spontaneous
electric polarization, that is, it maintains a non-zero electric
polarization in the absence of an electric field. Example
ferroelectric materials include barium titanate (BaTiO3), lead
titanate (PbTiO3), lead zirconium titanate (PZT), and strontium
bismuth tantalate (SBT). The ferroelectric capacitors described
herein may include these or other ferroelectric materials. Electric
polarization within a ferroelectric capacitor results in a net
charge at the ferroelectric material's surface and attracts
opposite charge through the capacitor terminals. Thus, charge is
stored at the interface of the ferroelectric material and the
capacitor terminals. Because the electric polarization may be
maintained in the absence of an externally applied electric field
for relatively long times, even indefinitely, charge leakage may be
significantly decreased as compared with, for example, capacitors
employed in DRAM arrays. This may reduce the need to perform
refresh operations.
[0075] Hysteresis curves 300-a and 300-b may be understood from the
perspective of a single terminal of a capacitor. By way of example,
if the ferroelectric material has a negative polarization, positive
charge accumulates at the terminal. Likewise, if the ferroelectric
material has a positive polarization, negative charge accumulates
at the terminal. Additionally, the voltages in hysteresis curves
300-a and 300-b represent a voltage difference across the capacitor
and are directional. For example, a positive voltage may be
realized by applying a positive voltage to the terminal in question
(e.g., a cell plate) and maintaining the second terminal (e.g., a
cell bottom) at ground (or approximately zero volts (0V)). A
negative voltage may be applied by maintaining the terminal in
question at ground and applying a positive voltage to the second
terminal--i.e., positive voltages may be applied to negatively
polarize the terminal in question. Similarly, two positive
voltages, two negative voltages, or any combination of positive and
negative voltages may be applied to the appropriate capacitor
terminals to generate the voltage difference shown in hysteresis
curves 300-a and 300-b.
[0076] As depicted in hysteresis curve 300-a, the ferroelectric
material may maintain a positive or negative polarization with a
zero-voltage difference, resulting in two possible charged states:
a charge state 305 and a charge state 310. According to the
examples of FIGS. 3A and 3B, charge state 305 represents a logic 0
and charge state 310 represents a logic 1. In some examples, the
logic values of the respective charge states may be reversed to
accommodate other schemes for operating a memory cell.
[0077] A logic 0 or 1 may be written to the memory cell by
controlling the electric polarization of the ferroelectric
material, and thus the charge on the capacitor terminals, by
applying voltage. For example, applying a net positive voltage 315
across the capacitor results in charge accumulation until charge
state 305-a is reached. Upon removing voltage 315, charge state
305-a follows path 320 until it reaches charge state 305 at zero
voltage. Similarly, charge state 310 is written by applying a net
negative voltage 325, which results in charge state 310-a. After
removing negative voltage 325, charge state 310-a follows path 330
until it reaches charge state 310 at zero voltage. Charge states
305-a and 310-a may also be referred to as the remnant polarization
(Pr) values, i.e., the polarization (or charge) that remains upon
removing the external bias (e.g., voltage). The coercive voltage is
the voltage at which the charge (or polarization) is zero.
[0078] To read, or sense, the stored state of the ferroelectric
capacitor, a voltage may be applied across the capacitor. In
response, the stored charge, Q, changes, and the degree of the
change depends on the initial charge state--i.e., the final stored
charge (Q) depends on whether charge state 305-b or 310-b was
initially stored. For example, hysteresis curve 300-b illustrates
two possible stored charge states 305-b and 310-b. Voltage 335 may
be applied across the capacitor 240 as discussed with reference to
FIG. 2. In other cases, a fixed voltage may be applied to the cell
plate and, although depicted as a positive voltage, voltage 335 may
be negative. In response to voltage 335, charge state 305-b may
follow path 340. Likewise, if charge state 310-b was initially
stored, then it follows path 345. The final position of charge
state 305-c and charge state 310-c depend on one or more factors,
including the specific sensing scheme and circuitry.
[0079] In some cases, the final charge may depend on the intrinsic
capacitance of the digit line connected to the memory cell. For
example, if the capacitor is electrically connected to the digit
line and voltage 335 is applied, the voltage of the digit line may
rise due to its intrinsic capacitance. A voltage measured at a
sense component may not equal voltage 335 and instead may depend on
the voltage of the digit line. The position of final charge states
305-c and 310-c on hysteresis curve 300-b may thus depend on the
capacitance of the digit line and may be determined through a
load-line analysis--i.e., charge states 305-c and 310-c may be
defined with respect to the digit line capacitance. As a result,
the voltage of the capacitor, voltage 350 or voltage 355, may be
different and may depend on the initial state of the capacitor.
[0080] By comparing the digit line voltage to a reference voltage,
the initial state of the capacitor may be determined. The digit
line voltage may be the difference between voltage 335 and the
final voltage across the capacitor, voltage 350 or voltage
355--i.e., the difference between the voltage 335 and the voltage
350 or the different between the voltage 335 and the voltage 355. A
reference voltage may be generated such that its magnitude is
between the two possible voltages of the two possible digit line
voltages to determine the stored logic state--i.e., if the digit
line voltage is higher or lower than the reference voltage. Upon
comparison by the sense component, the sensed digit line voltage
may be determined to be higher or lower than the reference voltage,
and the stored logic value of the ferroelectric memory cell (i.e.,
a logic 0 or 1) may be determined.
[0081] In some cases, a ferroelectric memory cell may maintain the
initial logic state after a read operation. For example, if charge
state 305-b is stored, the charge state may follow path 340 to
charge state 305-c during a read operation and, after removing
voltage 335, the charge state may return to initial charge state
305-b by following path 340 in the opposite direction. In some
cases, a ferroelectric memory cell may lose its initial logic state
after a read operation. For example, if charge state 310-b is
stored, the charge state may follow path 345 to charge state 305-c
during a read operation and, after removing voltage 335, the charge
state may relax to the charge state 305-b by following path
340.
[0082] Hysteresis curve 300-b illustrates an example of reading a
memory cell that is configured to store the charge state 305-b and
the charge state 310-b. A read voltage 335 may be applied, for
example, as a voltage difference via a digit line 215 and a plate
line 220 as described with reference to FIG. 2. Hysteresis curve
300-b may illustrate read operations where the read voltage 335 is
negative voltage difference Vcap (e.g., where Vbottom-Vplate is
negative). A negative read voltage across the capacitor may be
referred to as a "plate high" read operation, where a plate line
220 is taken initially to a high voltage, and a digit line 215 is
initially at a low voltage (e.g., a ground voltage). Although read
voltage 335 is shown as a negative voltage across the ferroelectric
capacitor 240, in alternative operations a read voltage may be a
positive voltage across the ferroelectric capacitor 240, which may
be referred to as a "plate low" read operation.
[0083] The read voltage 335 may be applied across the ferroelectric
capacitor 240 when a memory cell 205 is selected (e.g., by
activating a switching component 245 as described with reference to
FIG. 2). Upon applying the read voltage 335 to the ferroelectric
capacitor 240, charge may flow into or out of the ferroelectric
capacitor 240 via the digit line 215 and plate line 220, and
different charge states may result depending on whether the
ferroelectric capacitor 240 was at charge state 305-a (e.g., a
logic 1) or at charge state 310-a (e.g., a logic 0).
[0084] FIG. 4 illustrates an example of a circuit 400 that supports
techniques for read operations in accordance with examples as
disclosed herein. The circuit 400 illustrates how a transistor pair
420 may be coupled with an offset cancellation component 430,
signal shift component 440, a reference shift component 445, a
latch 460 and circuitry that may accompany such a configuration.
The circuit 400 may include one or more components described herein
with reference to FIGS. 1, 2 and 3. For example, the circuit 400
may include a memory cell 405, which may be an example memory cell
205 described with reference to FIG. 2; a digit line 410, which may
be an example of digit line 215 as described with reference to FIG.
2; a transistor pair 420, a offset cancellation component 430; a
signal shift component 440 associated with a signal node 450 (e.g.,
memory node); a reference shift component 445 associated with a
reference node 455; and a latch 460. In some examples, the
transistor pair 420 may be referred to as a signal transistor 421
and a reference transistor 422. The circuit 400 may also include
precharge voltage source 402, and an input voltage source 403.
[0085] The transistor pair 420 may include a signal transistor 421
and a reference transistor 422. In some cases, the signal
transistor 421 and reference transistor 422 may each be a source
follower circuit. In this regard, charge/voltage transferred to the
output node (represented by arrows) of each of signal transistor
421 and reference transistor 422 may be proportional to the voltage
applied to the gate of the transistor. Further, in some cases,
signal transistor 421 may have a first threshold drop between the
gate and the output node and reference transistor 422 may have a
second threshold drop, that is different than the first threshold
drop, between the gate and the output node. Thus, different voltage
drops may occur for charged transferred by each of the signal
transistor 421 and reference transistor 422. Accordingly, circuit
400 may include an offset cancellation component 430, which may be
configured to cancel out the mismatched threshold voltage drops for
different transistor pair 420. As a result, a signal voltage
applied to a first latch input 461 and reference voltage applied to
a second latch input 462 may have decreased variability due to
differences in the thresholds of the signal transistor 421 and
reference transistor 422.
[0086] The transistor pair 420 may be configured to couple a signal
node 450 to a first latch input 461 and a reference node 455 to a
second latch input 462. Further, circuit 400 may include a signal
shift component 440 (e.g., amplification circuit) coupled to signal
node and reference shift component 445 (e.g., amplification
circuit) coupled to reference node. Accordingly, a voltage stored
at memory cell 405 may be modified (e.g., amplified, shifted,
offset, etc.) by one or more components of circuit 400 before being
input to first latch input 461. Similarly, a reference voltage may
be modified (e.g., amplified, shifted, offset, etc.) by one or more
components of circuit 400 before being input to second latch input
462. In this regard, circuit 400 may be configured to develop a
signal voltage associated with a logic state (e.g., logic 0 or
logic 1) and a reference voltage at latch 460 inputs that provides
an improved sense voltage offset between a signal voltage
representing a logic state and the reference voltage.
[0087] The circuit 400 may further include multiple switches (e.g.,
415, 417, 432, 434, 436, 438, 464, and 465) configured to couple
and decouple different portions/nodes of circuit 400 during
operation of circuit 400 (e.g., during a read operation). The
switches selectively couple different nodes together at different
times to allow each transistor of the transistor pair 420 to
compensate for the other transistor's threshold voltage. That is,
in some cases, operation of circuit 400, may include opening
different switches at different times during a read operation in
order to couple and decouple different portions of circuit 400. In
some cases, circuit 400 may include switches that couple and
decouple the circuit 400 from one or more voltage sources. For
example circuit 400 may include precharge switches 415, which
couple precharge voltage source 402 to transistor pair 420 and
input switches 417, which couple input voltage source 403 to
transistor pair 420. The circuit 400 may also include switch that
couple and decouple signal node 450 to reference node 455, which
may be referred to as a cross-coupling operation. For example,
offset cancellation component 430 may also include a first offset
switch 432, a second offset switch 434, a third offset switch 436
and a fourth offset switch 438. Different switches may be operated
to couple reference output node 424 to signal node 450 or signal
output node 423 to reference node 455. In some cases, circuit 400
may also include one or more switches to couple and decouple a
latch 460 from the transistor pair 420. For example, first latch
switch 464 may couple and decouple signal output node 423 to first
latch input 461 and second latch switch 465 may couple and decouple
reference output node 424 to second latch input 462. A digit line
switch 412 may also couple digit line 410 to signal node 450. Each
switch may be one or more transistors, diodes, rectifiers, triacs,
or the like, or a combination thereof. In some example one or more
switches may be operated by one or more controllers. Additionally
or alternatively, one or more switches may operate in an analog
mode, for example, where electrical signals from one or more parts
of circuit 400 or signals from other parts of memory device
active/deactivate the switches (e.g., transistor being active by
having voltage applied to gate).
[0088] The transistor pair 420 may facilitate inputting a signal
voltage and reference voltage to latch 460 to determine a logic
state stored in memory cell 405 during a read operation. For
example, signal transistor 421 may have an input coupled to input
voltage source 403, an output coupled to signal output node 423 and
a gate coupled to precharge voltage source 402 or signal node 450.
A signal charge (e.g., charge associated with a logic state stored
on memory cell 405) may be transferred between digit line 410 and
the gate of signal transistor 421 during a read operation. Further,
the signal charge may be transferred from the gate of signal
transistor 421 (e.g., charge from precharge voltage source 402 or
signal node 450) to signal output node 423 based on the operation
of input switch 417-a to couple and decouple input voltage source
403 to the input of signal transistor 421. Similarly, a reference
charge (e.g., charge associated with a reference voltage source)
may be transferred between reference node 455 and the gate of
reference transistor 422. Further, reference transistor 422 may
have an input coupled to input voltage source 403, an output
coupled to reference output node 424 and a gate coupled to
precharge voltage source 402 or reference node 455. A reference
charge may be transferred from the gate of reference transistor 422
(e.g., charge from precharge voltage source 402 or reference node
455) to reference output node 424 based on operation of input
switch 417-b to couple and decouple input voltage source 403 to the
input of reference transistor 422.
[0089] The operation of transferring a signal charge from the gate
of signal transistor 421 to signal output node 423 may modify
(e.g., decrease) the signal charge by a first threshold effect of
signal transistor 421. Similarly, the operation of transferring a
reference charge from the gate of reference transistor 422 to
reference output node 424 may modify (e.g., decrease) the reference
charge by a second threshold effect of reference transistor 422.
Thus, a signal charge transferred to signal output node 423 may be
independently effected by the signal transistor 421 threshold and a
reference charge transferred to reference output node 424 may be
independently effected by reference transistor 422 threshold, thus
creating a threshold mismatch between a signal charge and a
reference charge.
[0090] In some cases, a read operation may include a precharge
phase (e.g., first phase) as part of an offset process to
compensate for threshold mismatch between transistor pair 420. For
example, at the first phase, the circuit 400 may be configured such
that offset cancellation component 430 may couple (e.g.,
cross-couple) reference output node 424 to signal node 450 and
signal output node 423 to reference node 455 to compensate for a
threshold mismatch between signal transistor 421 and reference
transistor 422. In some cases, a first offset switch 432 may be
coupled with reference output node 424 and signal node 450 and
configured to selectively couple and decouple reference output node
424 to signal node 450. A second offset switch 434 may be coupled
with signal output node 423 and reference node 455 and configured
to selectively couple and decouple signal output node 423 to
reference node 455. Further, in some cases, first precharge switch
415-a may couple precharge voltage source 402 to the gate of signal
transistor 421 and second precharge switch 415-b may couple
precharge voltage source 402 to the gate of reference transistor
422. Additionally or alternatively, during the first phase, third
offset switch 436 may be deactivated to decouple signal node 450
from the gate of signal transistor 421, fourth offset switch 438
may be deactivated to decouple reference node 455 from the gate of
reference transistor 422, first latch switch 464 may be deactivated
to decouple signal output node from first latch input 461 and
second latch switch 465 may be deactivated to decouple reference
output node from second latch input 462.
[0091] Accordingly, during a read operation, each of the signal
node 450 and reference node 455 may be precharged by cross-coupling
reference node 455 to the precharge voltage source 402-a coupled to
the gate of signal transistor 421 and signal node 450 to the
precharge voltage source 402-b coupled to the gate of reference
transistor 422.
[0092] Additionally or alternatively, a digit line switch 412 may
be coupled with the digit line 410 and the signal node 450 and
configured to selectively couple and decouple digit line 410 to
signal node 450. During a read operation a charge associated with
voltage signal stored on memory cell 405 representing a logic state
(e.g., logic 1 or logic 0) may be read/transferred to digit line
410. Further, during the read operation, digit line 410 may be
coupled to signal node 450 thereby transferring the signal charge
(e.g., associated with a logic state) between digital line and
signal node 450.
[0093] Circuit 400 may be operated (e.g., by a controller) to
couple first precharge voltage source 402-a to the gate of signal
transistor 421 by activating first precharge switch 415-a, couple
input voltage source 403-a to the input of signal transistor 421 by
activating first input switch 417-a, and couple signal output node
423 to reference node 455 by activating first offset switch 432. In
this regard, a signal precharge that is modified by the signal
transistor 421 threshold may be transferred to reference node 455.
Additionally or alternatively, circuit 400 may be further operated
to couple second precharge voltage source 402-b to the gate of
reference transistor 422 by activating second precharge switch
415-b, couple input voltage source 403-b to the input of reference
transistor 422 by activating second input switch 417-b, and couple
reference output node 424 to signal node 450 by activating second
offset switch 434. In this regard, a reference precharge that is
modified by the reference transistor 422 threshold may be
transferred to signal node 450. In some cases, circuit 400 may be
operated to activate digit line switch 412 to transfer a signal
charge associated with a logic state stored at memory cell 405
between the digit line 410 and signal node 450. In some cases, a
reference precharge transferred from reference output node 424 may
modify (increase or decrease) a signal charge (e.g., associated
with a logic state) transferred to signal node 450 from digit line
410.
[0094] In some cases, after the reference precharge has been
transferred between reference output node 424 and signal node 450,
first offset switch 432 may be deactivated thereby decoupling
reference output node 424 from signal node 450. Similarly, after
signal precharge has been transferred between signal output node
423 and reference node 455, second offset switch 434 may be
deactivated thereby decoupling signal output node 423 from
reference node 455. Additionally or alternatively, one or more of
precharge switches 415 or input switches 417 may also be
deactivated thereby decoupling the precharge voltage source 402
from the gates of the transistor pair 420 and input voltage source
403 from the inputs of transistor pair 420.
[0095] Circuit 400 may be configured to perform a second phase of a
read operation that includes developing (e.g., modifying) the
signal voltage and reference voltage before transferring a signal
charge and reference charge to latch 460. Accordingly, the circuit
400 may include a third offset switch 436 coupled with signal node
450 and the gate of signal transistor 421 and configured to
selectively couple signal node 450 with the gate of signal
transistor 421. A fourth offset switch 438 may be coupled with
reference node 455 and the gate of reference transistor 422 and
configured to selectively couple reference node 455 with the gate
of reference transistor 422. In some cases, during the second
phase, precharge switches 415 and input switches 417 may be
deactivated thereby decoupling precharge voltage source 402 and
input voltage source 403. In some cases, first offset switch 432
and second offset switch 434 may be deactivated thereby decoupling
signal node from reference output node 424 and reference node 455
from signal output node 423. In some cases, first latch switch 464
and second latch switch 465 may remain deactivated.
[0096] Additionally or alternatively, a signal shift component 440
may be coupled to signal node 450 and a reference shift component
445 may be coupled to reference node 455. Signal shift component
440 may be operable to transfer a charge to signal node (e.g.,
boost the voltage of signal node) thereby modifying (e.g.,
increasing) a charge at signal node 450. Reference shift component
445 may be operable to transfer charge to or from (e.g., shift or
boost the voltage of signal node) thereby modifying (e.g.,
decreasing or increasing) a charge at reference node 455. For
example, at a first time of the second phase, reference shift
component 445 may be operable to shift the charge at reference node
455 to decrease a voltage level on reference node 455. Such
operation may be performed to develop a reference voltage offset
between the reference voltage and the signal voltage to is input to
latch 460. At a second time, signal shift component 440 may be
operable to boost the signal charge at signal node 450 to increase
a voltage level on the signal node 450 and reference shift
component 445 may be operable to boost the reference charge at
reference node 455 to increase a voltage level on reference node
455. Such operation may be performed to develop the signal voltage
and reference voltage response before being input to latch 460.
[0097] Circuit 400 may be operated (e.g., by a controller) to
couple signal node 450 to the gate of signal transistor 421 by
activating third offset switch 436 and couple reference node 455 to
the gate of reference transistor 422 by activating fourth offset
switch 438. As a result, a signal charge (e.g., precharge voltage
offset by the reference transistor threshold from phase 1) at
signal node 450 may be transferred to the gate of signal transistor
421 thereby biasing the gate of the signal transistor 421 to a
signal voltage level. A reference charge (e.g., precharge voltage
offset by the signal transistor threshold from phase 1) at
reference node 455 may also be transferred to the gate of reference
transistor 422 thereby biasing the gate of reference transistor 422
to a reference voltage level. Additionally or alternatively, at a
first time, reference shift component 445 may be operated to
transfer a charge from reference node 455 to decrease a reference
voltage level at reference node 455, thereby decreasing the
reference voltage biasing the gate of reference transistor 422 via
the activated fourth offset switch 438. At a second time, signal
shift component 440 may be operated to transfer a charge to the
signal node 450 thereby increasing a signal voltage level biasing
the gate of signal transistor 421 and reference shift component 445
may be operated to transfer a charge to the reference node 455
thereby increasing the reference voltage level biasing the gate of
reference transistor 422.
[0098] In some cases, at a third time, word line transistor 407 may
be activated thereby transferring a charge stored on memory cell
405 to the gate of signal transistor 421 via activated digit line
switch 412 and third offset switch 436. In some examples the third
time occurs after the shift operations performed during the second
time. As a result, the signal voltage level biasing the gate of
signal transistor 421 may by modified (e.g., increased or
decreased) based on the charge stored on memory cell 405. The
charge stored on memory cell 405 may be based on a logic state
(e.g., logic 1 or logic 0) stored on memory cell 405 and thus, a
charge stored to indicate a first memory state (e.g., logic 1) may
modify the signal voltage level differently than a charge stored
indicate a second memory state (e.g., logic 0).
[0099] In some cases, circuit 400 may be configured to perform a
third phase of the read operation that includes compensating for
the threshold mismatch of transistor pair 420 before sampling the
signal voltage and reference voltage to latch 460. For example,
circuit 400 may include first latch switch 464 coupled with signal
output node 423 and first latch input 461 and configured to
selectively couple and decouple signal output node 423 to first
latch input 461. Circuit 400 may also include a second latch switch
465 coupled with reference output node 424 and second latch input
462 and configured to selectively couple and decouple reference
output node 424 to second latch input 462. During the third phase,
circuit may be configured such that input switches 417, third
offset switch 436, fourth offset switch 438, first latch switch
464, and second latch switch 465 are activated thereby coupling the
signal node 450 with first latch input 461 and reference node 455
with second latch input 462. Additionally or alternatively,
precharge switches 415, first offset switch 432, second offset
switch 434, and digit line switch may be deactivated thereby
decoupling precharge voltage source 402 from circuit 400 and memory
cell 405 from signal node 450. Further, in some cases, first offset
switch 432 and second offset switch 434 may remain deactivated such
that signal node 450 remains decoupled from reference output node
424 and reference node 455 remains decoupled from signal output
node 423.
[0100] Circuit 400 may be operated to couple input voltage source
403-a with the input of signal transistor 421 via activating first
input switch 417-a. Signal transistor 421 may become active and
transfer a signal output charge to signal output node 423. The
signal output charge may be based on the signal charge at the gate
of signal transistor 421. For example, the signal output charge may
be proportional to the signal charge at the gate of signal
transistor 421 and be modified (e.g., decreased) by the threshold
drop associated with signal transistor 421. In this regard, signal
output charge may be based on both the threshold from reference
transistor 422 as a result of the precharge configuration (e.g.,
first phase) of circuit 400 and the threshold from signal
transistor 421 as a result of the third phase configuration of
circuit 400.
[0101] Circuit 400 may further be operated to couple input voltage
source 403-b with the input of reference transistor 422 via
activating second input switch 417-b. Reference transistor 422 may
become active and transfer a reference output charge to reference
output node 424. The reference output charge may be based on the
reference charge at the gate of the reference transistor 422. For
example, the reference output charge may be proportional to the
reference charge at the gate of reference transistor 422 and be
modified (e.g., decreased) by the threshold drop associated with
reference transistor 422. In this regard, reference output charge
may be based on both the threshold from signal transistor 421 as a
result of the precharge configuration (e.g., first phase) of
circuit 400 and the threshold from reference transistor as a result
of the third phase configuration. Accordingly, each of the signal
output charge and reference output charge are based on both the
signal transistor 421 threshold and reference transistor 422
threshold, which may effectively result in compensating for the
threshold mismatch between the transistor pair 420.
[0102] In some cases, in the third phase, circuit 400 may be
operated to activate first latch switch 464 thereby coupling signal
output node 423 to first latch input 461 resulting in the signal
output charge being sampled to latch 460. Similarly, second latch
switch 465 may be activated thereby coupling reference output node
424 to second latch input 462 resulting in the reference output
charge being sample to latch 460. Accordingly, a voltage difference
between the reference voltage level and the signal voltage level
may be used to determine a logic state stored on memory cell
405.
[0103] FIG. 5 illustrates a timing diagram 500 that supports
techniques for read operations in accordance with examples as
disclosed herein. The timing diagram 500 illustrates procedures of
a read operation to sense a logic state stored on a memory cell
405. The timing diagram 500 shows various voltage levels (e.g.,
voltage signals as a function of time) associated with the
components and the nodes of the circuit 400 described with
reference to FIG. 4 to illustrate how the read operation may be
performed. Thus, the timing diagram 500 may illustrate the
operation of one or more components described herein with reference
to FIGS. 1, 2, and 3. The time and voltage scales used in FIG. 5
are for illustration purposes only and may not necessarily depict
particular values in some cases.
[0104] The timing diagram includes V_SIG 550 (e.g., a voltage of
the signal node 450 described with reference to FIG. 4), V_REF 555
(e.g., a voltage of the reference node 455 described with reference
to FIG. 4), V_pch 502 (e.g., a voltage of the precharge voltage
source 402 described with reference to FIG. 4), V_SSC 540 (e.g., a
voltage the signal shift component 440 described with reference to
FIG. 4), V_RSC 545 (e.g., a voltage of the reference shift
component 445 described with reference to FIG. 4), V_MG 561 (e.g.,
a voltage sampled to the first latch input 461 described with
reference to FIG. 4) and V_RG 562 (e.g., a voltage sampled to the
second latch input 462 described with reference to FIG. 4).
[0105] In some cases, the switches described with reference to FIG.
4 may be transistors or require an activation voltage to transition
between active and inactive states, as used herein Von refers to a
voltage greater than or equal to a transistor's threshold voltage
to activate the transistor or an activation voltage required to
active the switch. Similarly, Voff refers to a voltage less than a
transistor's threshold voltage to deactivate the transistor or a
deactivation voltage for a switch. Accordingly, the timing diagram
500 includes V_GPC 515 (e.g., a control voltage applied to
precharge switches 415 as described with reference to FIG. 4),
V_GIN 517 (e.g., a control voltage applied to input switches 417
described with reference to FIG. 4), V_OSF 532 (e.g., a control
voltage applied to first offset switch 432 and second offset switch
434 described with reference to FIG. 4), V_OSS 536 (e.g., a control
voltage applied to third offset switch 436 and fourth offset switch
438 described with reference to FIG. 4), V_WL 514 (e.g., a control
voltage applied to word line transistor 407 described with
reference to FIG. 4), V_DL 512 (e.g., a control voltage applied to
digit line switch 412 described with reference to FIG. 4) and V_LI
560 (e.g., a control voltage applied to first latch switch 464 and
second latch switch 465 described with reference to FIG. 4).
[0106] Before T1 (e.g., before precharging the signal node 450 and
reference node 455), the reference shift component 445 may be
activated to a reference offset voltage (e.g., V_ro), signal shift
component 440 may be biased to a ground voltage (e.g., V_ss) and
precharge voltage source 402 may be biased to a precharge voltage
(e.g., V_pch).
[0107] At time T1, a first phase 570 (e.g., Phase 1) may begin and
each transistor (e.g., signal transistor 421 and reference
transistor 422) in the transistor pair 420 may compensate for the
voltage threshold of the other transistor through charge sharing.
For example, precharge switches 415, input switches 417, and first
and second offset switches 432, 434 are activated. As a result,
precharge voltage 402 subjected to the reference transistor 422
threshold drop is applied to signal node 450 and a precharge
voltage 402 subjected to the signal transistor 421 threshold drop
is applied to the reference node 455. Thus, at the end of the first
phase the signal node 450 is storing a voltage that includes the
threshold effect from the reference transistor 422 and the
reference node 455 is storing a voltage that include a threshold
effect from the signal transistor 421. During the first phase 570
precharge switches 415 may be activated--e.g., V_GPC 515
corresponds to Von--to bias the each of the gates of transistor
pair 420 (e.g., gate of signal transistor 421 and gate of reference
transistor 422) to a first precharge voltage (e.g., V_pch). Input
switches 417 may be activated--e.g., V_GIN 517 corresponds to
Von--and first offset switch 432 and second offset switch 434 may
be activated--e.g., V_OSF 532 corresponds to Von--to couple
precharge voltage source 402 to the signal node 450 via reference
transistor 422 and first offset switch 432. Likewise, precharge
voltage source 402 is coupled to reference output node 424 via
signal transistor 421 and second offset switch 434. Accordingly,
signal voltage 550 (V_SIG) at signal node 450 is charged to
reference precharge voltage (V_pch)) and reference voltage 555
(V_REF) at reference node 455 is charged to precharge voltage
(V_pch). At the end of the first phase 570, signal voltage 550 is
offset from the precharge voltage (V_pch) by the reference
transistor threshold (Vth_ref). For example, the signal voltage 550
at the signal node 450 is equal to the precharge voltage minus the
reference transistor threshold--e.g., VSIG=V_pch-Vth_ref.
Similarly, at the end of the first phase 570, reference voltage 555
is offset from the precharge voltage (V_pch) by the signal
transistor threshold (Vth_sig). For example, the reference voltage
555 at the reference node is equal to the precharge voltage minus
the signal transistor threshold--e.g., V_REF=V_pch-Vth_sig.
[0108] In some cases, digit line switch 412 may be activated--e.g.,
V_DL 512 corresponds to Von--accordingly digit line may be coupled
to signal node and be precharged to signal voltage 550 (e.g.,
V_pch-Vth_ref).
[0109] At time T2, a second phase 575 (e.g., Phase 2) may begin and
the reference shift component 445 may be activated to decrease the
reference voltage (V_REF) at the reference node 455 to offset the
reference voltage (V_REF) from the signal voltage (V_SIG). This
step may develop a reference voltage offset from the signal voltage
that aids determination of the stored memory state based on a
response of the reference voltage at a later phase of the read
operation. During T2 of the second phase, precharge switches 415,
input switches 417, first offset switch 432 and second offset
switch 434 may be deactivated--e.g., V_GPC 515, V_GIN 517 and V_OSF
532 correspond to Voff--deactivating signal transistor 421 and
reference transistor. Also, third offset switch 436 and fourth
offset switch 438 may be activated--e.g., V_OSS corresponds to
Von-biasing the gate of signal transistor 421 to signal voltage 550
and the gate of reference transistor 422 to reference voltage 555.
Additionally, during the second phase 575 reference shift component
445 may be activated and driven driving the reference shift voltage
545 (e.g., V_RSC) to a ground voltage (V_ss). Accordingly, the
reference node 455 may be discharged, decreasing the reference
voltage 555 by offset voltage 556 from signal voltage 550.
[0110] At time T3 of the second phase 575, reference shift
component 445 may be activated to increase the reference voltage
and signal shift component 440 may be activated to increase the
signal voltage before activating the world line transistor 407 to
transfer a charge stored on memory cell 405 to the signal node 450.
During T3 of the second phase, the reference shift component 445
may be activated to increase reference shift voltage 545 (e.g.,
V_RCS) to an increased voltage level (e.g., V_boost) thereby
charging reference node 455 and increasing the reference voltage
555 biasing the gate of reference transistor 422. Similarly, signal
shift component 440 may be activated to drive signal shift voltage
540 (e.g., V_SCS) to an increased voltage level (e.g., V_boost)
thereby charging signal node 450 and increasing the signal voltage
550 biasing the gate of signal transistor 421.
[0111] At time T4 of the second phase 575, a charge indicating a
memory state (e.g., logic 1 or logic 0) stored on memory cell 405
may be transferred to signal node 450. As a result, the signal
voltage may change based on the charge stored on the memory cell
405. During T4 of the second phase word line transistor 407 may be
activated--e.g., V_WL 514 corresponds to Von--to bias the gate of
signal transistor 421 based on a charge stored at memory cell 405.
That is, if a charge corresponding to a first logic state (e.g.,
logic 1) is stored on memory cell 405 then the signal voltage 550
may decrease according to a first signal voltage response 550-a. If
a charge corresponding to a second logic state (e.g., logic 0) is
stored on memory cell 405 then the signal voltage 550 may decrease
according to a second signal voltage response 550-b.
[0112] At time T5 a third phase 580 (e.g., phase 3) may begin and
the signal voltage at signal node 450 and the reference voltage at
reference node 455 may be sampled to latch 460 by activating the
transistor pair 420. During the third phase word line transistor
407 and digit line switch 412 may be deactivated--e.g., V_WL and
V_DL correspond to Voff--thereby isolating memory cell 405 from the
gate of signal transistor 421. Also, input switches 417 and latch
switches 464, 465 may be activated--e.g., V_GIN 517 and V_LI 560
correspond to Von-activating signal transistor 421 and reference
transistor 422 thereby sampling the signal voltage 550 to first
latch input 461 and reference voltage 555 to second latch input
462.
[0113] FIG. 6A-6C illustrate examples of the circuit 600
configurations (e.g., coupled and decoupled components) for each of
the three phases discussed with reference to FIGS. 4 and 5 that
support techniques for read operations in accordance with examples
as disclosed herein. The circuit 600 may include one or more
components described with reference to FIGS. 1-5. For example,
circuit 600 may include a signal transistor 621, which may be an
example of signal transistor 421 described with reference to FIG.
4, a reference transistor 622, which may be an example of reference
transistor 422 described with reference to FIG. 4, precharge
voltage source 602, which may be an example of precharge voltage
source 402 described with reference to FIG. 4, or precharge voltage
(V_pch) described with reference to FIG. 5, input voltage source
603, which may be an example of input voltage source 403 described
with reference to FIG. 4, memory cell 605, which may be an example
of memory cell 405 described with reference to FIG. 4, and signal
node 650 and reference node 655, which may be examples of signal
node 450 and reference node 455 described with reference to FIG.
4.
[0114] FIG. 6A illustrates circuit configuration 600-a that may be
implemented for a first phase of a read operation. At the first
phase, precharge switches 615, input switches 617, first offset
switch 632, second offset switch 634 and digit line switch 612 may
all be activated. As a result, precharge voltage source 602 and
input voltage source 603 may be coupled to reference node 655 via
signal transistor 621. Additionally or alternatively, precharge
voltage source 602 and input voltage source 603 may be coupled to
signal node 650 via reference transistor 622. In some cases, third
offset switch 636 may be deactivated thereby decoupling signal node
650 from the gate of signal transistor 621 and fourth offset switch
638 may be deactivated thereby decoupling reference node 655 from
the gate of reference transistor 622. In some cases, first latch
switch 664 and second latch switch 665 may be deactivated thereby
decoupling first latch input 661 from signal output node 623 and
second latch input 662 from reference output node 624.
[0115] In some examples, signal transistor 621 and reference
transistor 622 may each be a source follower circuit. In this
regard, in the first phase configuration, precharge voltage (V_pch)
may be transferred to signal node 650 via reference transistor 622.
Accordingly, the voltage at signal node 650 may include an offset
due to the reference transistor threshold (Vth_ref). In this
regard, the voltage at signal node during the first phase may be
estimated as Equation 1 shown below.
V_SIG=V_pch-Vth_ref (1)
[0116] In some examples, precharge voltage (V_pch) may be
transferred to reference node 655 via signal transistor 621.
Accordingly, the voltage at reference node 655 may include an
offset due to the signal transistor threshold (Vth_sig). In this
regard, the voltage at reference node during the first phase may be
estimated as Equation 2 shown below.
V_REF=V_pch-Vth_sig. (2)
[0117] FIG. 6B illustrates circuit configuration 600-b that may be
implemented for a second phase of a read operation. At the second
phase, precharge switches 615, input switches 617 thereby
decoupling precharge voltage source 602 and input voltage source
603 from circuit 600. First offset switch 632 and second offset
switch 634 may be deactivated thereby decoupling signal output node
623 from reference node 655 and reference output node 624 from
signal node 6. First and second latch switches 664, 665 may remain
decoupled. Third offset switch 636 may be activated coupling signal
node 650 to the gate of signal transistor 621 and fourth offset
switch 638 may be activated coupling reference node 655 to the gate
of reference transistor 622.
[0118] In some examples, signal shift component 640 may apply a
voltage increase (e.g., V_boost) to signal node 650, such as
described with reference to signal shift component 440 described in
FIGS. 4 and 5. Reference shift component 645 may also apply a
voltage shift (e.g., Vref_shift) and voltage increase (e.g.,
V_boost) to reference node 655, such as described with reference to
reference shift component 445 in FIGS. 4 and 5. In some cases, word
line transistor 607 may also be activated applying a stored voltage
(V_mem) from memory cell 605 on signal node 650.
[0119] Activating third offset switch 636 may bias the gate of
signal transistor 621 to include the voltage on signal node 650
(e.g., V_pch-Vth_ref), the voltage increase from signal shift
component 640 (e.g., V_boost) and the voltage from memory cell 605
(V_mem). Accordingly, at the second phase, the voltage biasing the
gate of signal transistor 621 may be estimated as Equation 3 shown
below.
V_SIG=V_pch-Vth_ref-.DELTA.V_mem+V_boost (3)
[0120] Activating fourth offset switch 638 may bias the gate of
reference transistor 622 to include the voltage on reference node
655 (e.g., V_pch-Vth_sig), the reference shift voltage from the
reference shift component 645 (e.g., Vref_shift) and the voltage
increase from reference shift component 645 (e.g., V_boost).
Accordingly, at the second phase, the voltage biasing the gate of
reference transistor 622 may be estimated as Equation 4 shown
below.
V_REF=V_pch-Vth_ref-Vref_shift+V_boost (4)
[0121] FIG. 6C illustrates circuit configuration 600-c that may be
implemented for a third phase of a read operation. At the third
phase, precharge switches 615, first offset switch 632 and second
offset switch 634 may remain deactivated. Input switches 617 may be
re-activated thereby activating signal transistor 621 and reference
transistor 622. First latch switch 664 may be activated coupling
signal output node 623 to first latch input 661 and second latch
switch 665 may be activated coupling reference output node 624 to
second latch input 662. In some cases, digit line switch 612 may be
deactivated decoupling memory cell 605 from signal node 650.
[0122] Activating signal transistor 621 and first latch switch 664
samples the voltage at the gate of signal transistor 621 to first
latch input 661, which may include the signal transistor threshold
(Vth_sig). Accordingly, at the third phase, the voltage sampled to
the first latch input 661 may be estimated as Equation 5 shown
below.
V_SIG=V_pch-Vth_ref-Vth_sig-.DELTA.V_mem+V_boost (5)
[0123] Activating reference transistor 622 and second latch switch
665 samples the voltage at the gate of reference transistor 622 to
second latch input 662, which may include the reference threshold
voltage (Vth_ref). Accordingly, at the third phase, the voltage
sampled to the second latch input may be estimated as Equation 6 as
shown below.
V_REF=V_pch-Vth_ref-Vth_sig-Vref_shift+V_boost (6)
[0124] In some cases, the difference between the signal voltage and
the reference voltage may be determined to be V_SIG-V_REF. Notably,
the precharge voltage (V_pch), reference transistor threshold
(Vth_ref), signal transistor threshold (Vth_sig) and voltage
increase (V_boost) cancel out. Thus, the voltage difference can be
estimate as Equation 7 as shown below.
V_DIFF=.DELTA.V_mem-Vref_shift (7)
[0125] In some examples, a logic state stored on memory cell 605
may be determined based on the value of V_Diff. For example, if
V_Diff falls within a first set of values, the memory device may be
determined to store a first logic state (e.g., logic 1) and if
V_Diff falls within a second set of values, the memory device may
be determined to store a second logic state (e.g., logic 0).
[0126] FIG. 7 illustrates an example of a circuit 700 that supports
techniques for read operations in accordance with examples as
disclosed herein. The circuit illustrates how a capacitive
reference component 770 may be coupled with a sensing circuit for
sampling a voltage stores on memory cell 705 to a latch 760. The
capacitive reference component 770 may develop a voltage response
on reference node 755 similar to the voltage response on a signal
node 750 from a digit line 710. In some aspects the capacitive
reference component 770 may eliminate the need for a reference
shift component 745 to shift a reference voltage before sampling to
a latch, for example, such as the shift process implemented by
reference shift component 445 or 645 which are described in
relation to FIGS. 4-6. Accordingly, variability in a sense process
may be reduced by removing differences between voltage responses on
separate shift components (e.g., signal shift component 440 or 640
that is independent from reference shift component 445 or 645 as
described with reference to FIGS. 4-6).
[0127] Circuit 700 may include one or more components described
with reference to FIGS. 1-6. For example, circuit 700 may include a
memory cell 705, which may be an example memory cell 205 described
with reference to FIG. 2 or memory cell 405 described with
reference to FIG. 4; a digit line 710, which may be an example of
digit line 215 as described with reference to FIG. 2; a transistor
pair 720; one or more shift components (e.g., signal shift
component 740 or reference shift component 745); a capacitive
reference component 770; and a latch 760. The circuit 700 may also
include precharge voltage source 702, a first reference voltage
source 780 (Vrc1) and a second reference voltage source 782
(Vrc2).
[0128] Circuit 700 may be configured in a variety of ways to
implement reference voltage adjustment. For example, in one
implementation, capacitive reference component 770 may include a
first source switch 776 to selectively couple capacitive reference
node 772 to a first reference voltage source 780. In this example,
a second source switch 778 may be a static connection to second
reference voltage source 782, for example, reference capacitor 774
may be coupled directly to a ground voltage (e.g., Vss). In a
second implementation, first source switch 776 may be replaced with
a static connection and second source switch 778 may selectively
couple and decouple second reference voltage source 782 to
reference capacitor 774 (and capacitive reference node 772). In
some cases, second reference voltage source 782 may be a ground
voltage (Vss).
[0129] In a first phase (e.g., precharge phase), circuit 700 may be
configured to bias transistor pair 720 to a first precharge voltage
(e.g., Vpch). In some cases, at the first phase, the precharge
switches 715 may be activated to couple precharge voltage source
702 with the gates of signal transistor 721 and reference
transistor 722. Input switches 717 may be deactivated, and thus,
transistor pair 720 may be inactive (e.g., not transferring any
charge). Further, at the first phase, signal shift component 740
may be coupled with reference shift component 745 (e.g., grounded
together). In some cases, a first transistor 785 is also
deactivated thereby decoupling capacitive reference component 770
from reference node 755.
[0130] Accordingly, during the first phase, the voltage at
reference node 755 may increase to the precharge voltage source
level (Vpch) and the voltage at signal node 750 may also increase
to the precharge voltage source level (Vpch). In some cases, digit
line switch 712 may be active thereby coupling digit line 710 to
signal node 750. Accordingly, the voltage at digit line 710 will
increase to a digit line voltage, which may be less than the
precharge voltage (Vpch), for example due to the capacitive
characteristic of digit line 710.
[0131] In a first implementation of capacitive reference component
770, first source switch 776 may be activated coupling capacitive
reference node 772 to first reference voltage source 780 and second
source switch may be a static connection to a ground voltage (e.g.,
Vss). Thus, reference capacitor 774 may be charged by first
reference voltage source 780 and capacitive reference node 772 may
charge to the first reference voltage source level (e.g.,
Vcrl).
[0132] In a second implementation of capacitive reference component
770, first source switch 776 may be a static connection to first
reference voltage source 780 and second source switch 778 may be
deactivated and thus capacitive reference node 772 is decoupled
from second reference voltage source 782. In this implementation,
reference capacitor 774 may be charged by first reference voltage
source 780 and capacitive reference node 772 may charge to the
first reference voltage source level (e.g., Vcrl).
[0133] In the first implementation of capacitive reference
component 770, first source switch 776 may have been deactivated
before entering a second phase, thereby decoupling capacitive
reference node 772 from first reference voltage source 780. In the
second implementation of capacitive reference component 770, second
source switch 778 may be activated before entering the second
phase, thereby coupling capacitive reference node 772 to second
reference voltage source 782, which may be a ground voltage (e.g.,
Vss).
[0134] At a second phase (e.g., phase 2), circuit 700 may be
configured to develop a signal voltage at signal node 750 and a
reference voltage at reference node 755 before sampling the signal
and reference voltages to latch 760. In this regard, at the second
phase, the precharge switches 715 may be deactivated decoupling
precharge voltage source from the gates of transistor pair 720.
Signal shift component 740 and reference shift component 745 may
transfer a charge to signal node 750 and reference node 755
increasing/boosting the voltage level on the nodes. At the second
phase, and after the signal shift component 740 and reference shift
component 745 have increased the voltage on signal node 750 and
reference node 755, word line transistor 707 may be activated
coupling memory cell 705 to signal node 750. Accordingly, the
voltage level at signal node 750 may be shifted based on a logic
value stored at memory cell 705. In relation to activating word
line transistor 707, first transistor 785 may also be activated
coupling capacitive reference node 772 to reference node 755. In
this regard, the voltage level on signal node 750 may decrease
based on a capacitive property of digit line 710, and the voltage
level on reference node 755 may decrease based on a capacitive
property of capacitive reference component 770. Accordingly, the
capacitive effect of capacitive reference node 772 can be
configured to develop a reference voltage response that is between
a first voltage response at signal node 750 (e.g., in response to a
first logic state stored at memory cell 705) and second voltage
response at signal node 750 (e.g., in response to a second logic
state stored at memory cell 705).
[0135] In some cases, a third stage may include sampling the
voltage at signal node 750 and reference node 755 to latch 760. For
example, sampling may occur as described with reference to FIGS.
4-6. Although, a first configuration of circuit 700 is shown, other
implementations may include different circuit configurations. For
example, the offset circuit described with reference to FIGS. 4-6
could be implement with the capacitive reference component 770 as
described with reference to FIG. 7.
[0136] FIG. 8 illustrates an example of a timing diagram 800 that
supports techniques for read operations in accordance with examples
as disclosed herein. The timing diagram 800 illustrates procedures
of a read operation to sense a logic state stored on a memory cell.
The timing diagram 800 shows various voltage levels (e.g., voltage
signals as a function of time) associated with the components and
the nodes of the circuit 700 described with reference to FIG. 7 to
illustrate how the read operation may be performed. Thus, the
timing diagram 800 may illustrate the operation of one or more
components described herein with reference to FIGS. 1, 2, and 3.
The time and voltage scales used in FIG. 8 are for illustration
purposes only and may not necessarily depict particular values in
some cases.
[0137] The timing diagram includes V_SIG 850 (e.g., a voltage of
the signal node 750 described with reference to FIG. 7), V_REF 855
(e.g., a voltage of the reference node 755 described with reference
to FIG. 7), Vpch (e.g., a voltage of the precharge voltage source
702 described with reference to FIG. 7), V_SC 843 (e.g., a voltage
of the signal shift component 740 and reference shift component 745
described with reference to FIG. 7), V_CN 872 (e.g., a voltage of
the capacitive reference node 772 described with reference to FIG.
7), and V_DL 810 (e.g., a voltage of the digit line 710 described
with reference to FIG. 7).
[0138] In some cases, the switches described with reference to FIG.
7 may be transistors or require an activation voltage to transition
between active and inactive states, as used herein Von refers to a
voltage greater than or equal to a transistor's threshold voltage
to activate the transistor or an activation voltage required to
active the switch. Similarly, Voff refers to a voltage less than a
transistor's threshold voltage to deactivate the transistor or a
deactivation voltage for a switch. Accordingly, the timing diagram
800 includes V_GPC 815 (e.g., a control voltage applied to
precharge switches 715 as described with reference to FIG. 7),
V_RS1 876 (e.g., a control voltage applied to first source switch
776 in a first implementation of capacitive reference component 770
described with reference to FIG. 7), V_RS2 878 (e.g., a control
voltage applied to second source switch 778 in a second
implementation of capacitive reference component 770 described with
reference to FIG. 7), V_DL 812 (e.g., a control voltage applied to
digit line switch 712 described with reference to FIG. 7), V_WL 807
(e.g., a control voltage applied to word line transistor 707
described with reference to FIG. 7), and V_RC 885 (e.g., a control
voltage applied to first transistor 785 described with reference to
FIG. 7).
[0139] Before T1 (e.g., before precharging the signal node 750 and
reference node 755) circuit 700 may be at a low or ground
voltage.
[0140] At time T1 a first phase 890 (e.g., Phase 1) may begin by
signal node 750 and reference node 755 being precharged to
precharge voltage (Vpch). Additionally, capacitive reference node
752 may be precharged to a reference offset voltage (Vrc) and digit
line 710 may be charged to a digit line voltage (Vdl). The
reference offset voltage (Vrc) may be set to develop a reference
voltage response (e.g., V_REF 855) that is similar to the
capacitive characteristics of digit line 710. Thus, the reference
node 755 may have a similar capacitive response to the signal node
750. During T1 of the first phase precharge switches 715 may be
activated--e.g., V_GPC 815 corresponds to Von-coupling signal node
750 and reference node 755 to precharge voltage source 702. In this
regard, signal voltage 850 (V_SIG) at signal node 750 increase to
Vpch and reference voltage 855 (V_REF) at reference node 755
increases to Vpch. Digit line switch 712 may also be
activated--V_DL 812 corresponds to Von--coupling digit line 710 to
signal node 750 In this regard, digit line voltage 810 increase to
Vdl.
[0141] Also, in a first implementation, first source switch 776 may
be activated--e.g., V_RS1 corresponds to Von-coupling first
reference voltage source 780 to capacitive reference node 772. In a
second implementation, second source switch 778 may be
deactivated--e.g., V_RS2 corresponds to Voff--decoupling second
reference voltage source 782 from capacitive reference node 772. In
either event, the capacitive reference node voltage 872 (V_CN) at
capacitive reference node 772 increases to Vrc (e.g., the voltage
of first reference voltage source 780).
[0142] Before transitioning to the second phase at T2, but after
V_SIG 850, V_REF 855, V_DL 810 and V_CN 872 have reached a steady
state or a set time has passed, first source switch 776 or second
source switch 778 may be activated or deactivated based on the
implementation. For example, in the first implementation, the first
source switch 776 is deactivated--e.g., V_RS1 corresponds to
Voff--decoupling first reference voltage source 780 from capacitive
reference node 772. In the second implementation, second source
switch 778 is activated--e.g., V_RS2 corresponds to Von--coupling
second reference voltage source 782 (e.g., Vss) to capacitive
reference node 772.
[0143] At time T2, the second phase 892 (e.g., Phase 2) may begin
by activating signal shift component 740 and/or reference shift
component 745, which may be short circuited, to increase the
voltage level at both the signal node 750 and reference node 755 by
the same amount. Precharge switches 715 may be deactivated--e.g.,
V_GPC 815 corresponds to Voff--decoupling precharge voltage source
from signal node 750 and reference node 755. Also, signal shift
component 740 and/or reference shift component 745 may activate a
boost signal 843 (V_SC increases to V_boost) increasing the voltage
of each of signal node 750 and reference node 755. Accordingly, the
signal voltage 850 (V_SIG) and reference voltage 855 (V_REF) may
increase based on the boost voltage (V_boost).
[0144] At time T3, a charge indicating a memory state (e.g., logic
1 or logic 0) stored on memory cell 705 may be transferred to
signal node 750. As a result, the signal voltage (e.g., V_SIG 850)
may change based on the charge stored on the memory cell 705.
During T3 word line transistor 707 may be activated--e.g., V_WL 807
corresponds to Von-coupling memory cell 705 to signal node 750. As
a result, a charge stored on memory cell representing a logic state
may cause a decrease in the signal voltage 850 in based on the
logic state that was stored on memory cell 705. For example, if a
first logic state (e.g., logic 1) was stored on memory device,
signal voltage 850 may decrease according to a first
response--e.g., V_SIG 850-a. If a second logic state (e.g., logic
1) was stored on memory device, signal voltage 850 may decrease
according to a second voltage response--e.g., V_SIG 850-b. Also, at
T3 first transistor 785 may be activated--e.g., V_RC corresponds to
Von-coupling capacitive reference node 772 to reference node 755.
As a result, the reference voltage 855 (V_REF) may decrease in
relation to the capacitive reference node voltage 872 (V_CN) stored
at reference capacitor 774. For example, capacitive reference node
772 may pull charge from reference node 755. In this regard,
reference voltage may decrease according to reference voltage 855
response and develop reference offset 856. Reference offset 856 may
be set by adjusting one or more parameter of capacitive reference
component 770 (e.g., properties of reference capacitor 774, first
reference voltage source 780, second reference voltage source 782,
or a combination thereof). Further, reference offset 856 may be set
to aid determination of the logic state stored at memory cell 705.
For example, reference voltage 855 may be set to be substantially
half way between first signal voltage response 850-a (e.g., logic
state 1) and second signal voltage response 850-b (e.g., logic
state 0).
[0145] At time T4 circuit 700 may sample signal voltage 850 and
reference voltage 855 to latch 760. This may occur as described
with reference to FIGS. 4-6, or according to another sense
operation.
[0146] FIG. 9 shows a block diagram 900 of a memory device 905 that
supports techniques for read operations in accordance with examples
as disclosed herein. The memory device 905 may be an example of
aspects of a memory device as described with reference to FIGS. 1
through 8. The memory device 905 may include a biasing manager 910,
an offset module 915, a memory read manager 920, a logic
determination module 925, a switch activation manager 930, and a
reference capacitor module 935. Each of these modules may
communicate, directly or indirectly, with one another (e.g., via
one or more buses).
[0147] The biasing manager 910 may bias a first gate of a first
transistor to a first voltage. In some examples, the biasing
manager 910 may bias a second gate of a second transistor to a
third voltage based on coupling the memory cell with the first
node.
[0148] The offset module 915 may precharge a first node to a second
voltage based on biasing the first gate of the first transistor to
the first voltage, the second voltage being based on the first
voltage and on a first threshold voltage of the first transistor.
In some examples, the offset module 915 may apply a fourth voltage
to a second node coupled with a latch and the second transistor
based on applying the third voltage to the second gate of the
second transistor, the fourth voltage being based on the third
voltage and a second threshold voltage of the second
transistor.
[0149] The memory read manager 920 may couple a memory cell with
the first node precharged to the second voltage based on
precharging the first node. In some examples, the memory read
manager 920 may apply a reference voltage to a latch during the
read operation based on coupling the first node to the second
node.
[0150] The logic determination module 925 may determine a logic
state stored on the memory cell based on applying the fourth
voltage to the second node coupled with the latch.
[0151] The switch activation manager 930 may couple a first node to
a first voltage source to increase the first node to a first
voltage level as part of a read operation of a memory cell. In some
examples, the switch activation manager 930 may couple a second
node to a second voltage source to increase the second node to a
second voltage level as part of the read operation of the memory
cell. The switch activation manager 930 may couple the first node
with the second node based on applying the voltage increase to the
first capacitor.
[0152] The reference capacitor module 935 may apply a voltage
increase to a first capacitor coupled with the first node to
increase a third voltage level of the first node based on coupling
the first node to the first voltage source.
[0153] FIG. 10 shows a flowchart illustrating a method or methods
1000 that supports techniques for read operations in accordance
with aspects of the present disclosure. The operations of method
1000 may be implemented by a memory device or its components as
described herein. For example, the operations of method 1000 may be
performed by a memory device as described with reference to FIG. 9.
In some examples, a memory device may execute a set of instructions
to control the functional elements of the memory device to perform
the described functions. Additionally or alternatively, a memory
device may perform aspects of the described functions using
special-purpose hardware.
[0154] At 1005, the memory device may bias a first gate of a first
transistor to a first voltage. The operations of 1005 may be
performed according to the methods described herein. In some
examples, aspects of the operations of 1005 may be performed by a
biasing manager as described with reference to FIG. 9.
[0155] At 1010, the memory device may precharge a first node to a
second voltage based on biasing the first gate of the first
transistor to the first voltage, the second voltage being based on
the first voltage and on a first threshold voltage of the first
transistor. The operations of 1010 may be performed according to
the methods described herein. In some examples, aspects of the
operations of 1010 may be performed by an offset module as
described with reference to FIG. 9.
[0156] At 1015, the memory device may couple a memory cell with the
first node precharged to the second voltage based on precharging
the first node. The operations of 1015 may be performed according
to the methods described herein. In some examples, aspects of the
operations of 1015 may be performed by a memory read manager as
described with reference to FIG. 9.
[0157] At 1020, the memory device may bias a second gate of a
second transistor to a third voltage based on coupling the memory
cell with the first node. The operations of 1020 may be performed
according to the methods described herein. In some examples,
aspects of the operations of 1020 may be performed by a biasing
manager as described with reference to FIG. 9.
[0158] At 1025, the memory device may apply a fourth voltage to a
second node coupled with a latch and the second transistor based on
applying the third voltage to the second gate of the second
transistor, the fourth voltage being based on the third voltage and
a second threshold voltage of the second transistor. The operations
of 1025 may be performed according to the methods described herein.
In some examples, aspects of the operations of 1025 may be
performed by an offset module as described with reference to FIG.
9.
[0159] At 1030, the memory device may determine a logic state
stored on the memory cell based on applying the fourth voltage to
the second node coupled with the latch. The operations of 1030 may
be performed according to the methods described herein. In some
examples, aspects of the operations of 1030 may be performed by a
logic determination module as described with reference to FIG.
9.
[0160] FIG. 11 shows a flowchart illustrating a method or methods
1100 that supports techniques for read operations in accordance
with aspects of the present disclosure. The operations of method
1100 may be implemented by a memory device or its components as
described herein. For example, the operations of method 1100 may be
performed by a memory device as described with reference to FIG. 9.
In some examples, a memory device may execute a set of instructions
to control the functional elements of the memory device to perform
the described functions. Additionally or alternatively, a memory
device may perform aspects of the described functions using
special-purpose hardware.
[0161] At 1105, the memory device may couple a first node to a
first voltage source to increase the first node to a first voltage
level as part of a read operation of a memory cell. The operations
of 1105 may be performed according to the methods described herein.
In some examples, aspects of the operations of 1105 may be
performed by a switch activation manager as described with
reference to FIG. 9.
[0162] At 1110, the memory device may couple a second node to a
second voltage source to increase the second node to a second
voltage level as part of the read operation of the memory cell. The
operations of 1110 may be performed according to the methods
described herein. In some examples, aspects of the operations of
1110 may be performed by a switch activation manager as described
with reference to FIG. 9.
[0163] At 1115, the memory device may apply a voltage increase to a
first capacitor coupled with the first node to increase a third
voltage level of the first node based on coupling the first node to
the first voltage source. The operations of 1115 may be performed
according to the methods described herein. In some examples,
aspects of the operations of 1115 may be performed by a reference
capacitor module as described with reference to FIG. 9.
[0164] At 1120, the memory device may couple the first node with
the second node based on applying the voltage increase to the first
capacitor. The operations of 1120 may be performed according to the
methods described herein. In some examples, aspects of the
operations of 1120 may be performed by a switch activation manager
as described with reference to FIG. 9.
[0165] At 1125, the memory device may apply a reference voltage to
a latch during the read operation based on coupling the first node
to the second node. The operations of 1125 may be performed
according to the methods described herein. In some examples,
aspects of the operations of 1125 may be performed by a memory read
manager as described with reference to FIG. 9.
[0166] In some examples, an apparatus as described herein may
perform a method or methods, such as the method 1100. The apparatus
may include features, means, or instructions (e.g., a
non-transitory computer-readable medium storing instructions
executable by a processor) for coupling a first node to a first
voltage source to increase the first node to a first voltage level
as part of a read operation of a memory cell, coupling a second
node to a second voltage source to increase the second node to a
second voltage level as part of the read operation of the memory
cell, applying a voltage increase to a first capacitor coupled with
the first node to increase a third voltage level of the first node
based on coupling the first node to the first voltage source,
coupling the first node with the second node based on applying the
voltage increase to the first capacitor, and applying a reference
voltage to a latch during the read operation based on coupling the
first node to the second node.
[0167] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for isolating the second node from the second voltage
source by deactivating a first transistor before coupling the first
node to the second node.
[0168] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for coupling the second node to a fourth voltage
source by activating a second transistor before coupling the first
node to the second node.
[0169] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for precharging a second capacitor coupled with the
second node based on the third voltage level associated with a
digit line coupled with the first node.
[0170] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for coupling, as part of the read operation, a third
node associated with the memory cell to a third voltage source to
increase the third voltage level of the third node, and coupling
the third node to a digit line to increase a fourth voltage level
of the digit line.
[0171] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for applying the voltage increase to a third capacitor
coupled with the third node based on coupling the third node to the
digit line.
[0172] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for applying a fifth voltage indicating a logic state
stored on the memory cell to the latch during the read operation
based at least in part applying the voltage increase to the first
capacitor and the third capacitor.
[0173] Some examples of the method 1100 and the apparatus described
herein may further include operations, features, means, or
instructions for determining the logic state stored on the memory
cell based on comparing the fifth voltage to the reference
voltage.
[0174] It should be noted that the methods described above describe
possible implementations, and that the operations and the steps may
be rearranged or otherwise modified and that other implementations
are possible. Furthermore, aspects from two or more of the methods
may be combined.
[0175] Information and signals described herein may be represented
using any of a variety of different technologies and techniques.
For example, data, instructions, commands, information, signals,
bits, symbols, and chips that may be referenced throughout the
above description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof. Some drawings may
illustrate signals as a single signal; however, it will be
understood by a person of ordinary skill in the art that the signal
may represent a bus of signals, where the bus may have a variety of
bit widths.
[0176] As used herein, the term "virtual ground" refers to a node
of an electrical circuit that is held at a voltage of approximately
zero volts (0V) but that is not directly coupled with ground.
Accordingly, the voltage of a virtual ground may temporarily
fluctuate and return to approximately 0V at steady state. A virtual
ground may be implemented using various electronic circuit
elements, such as a voltage divider consisting of operational
amplifiers and resistors. Other implementations are also possible.
"Virtual grounding" or "virtually grounded" means connected to
approximately 0V.
[0177] The terms "electronic communication," "conductive contact,"
"connected," and "coupled" may refer to a relationship between
components that supports the flow of signals between the
components. Components are considered in electronic communication
with (or in conductive contact with or connected with or coupled
with) one another if there is any conductive path between the
components that can, at any time, support the flow of signals
between the components. At any given time, the conductive path
between components that are in electronic communication with each
other (or in conductive contact with or connected with or coupled
with) may be an open circuit or a closed circuit based on the
operation of the device that includes the connected components. The
conductive path between connected components may be a direct
conductive path between the components or the conductive path
between connected components may be an indirect conductive path
that may include intermediate components, such as switches,
transistors, or other components. In some cases, the flow of
signals between the connected components may be interrupted for a
time, for example, using one or more intermediate components such
as switches or transistors.
[0178] The term "coupling" refers to condition of moving from an
open-circuit relationship between components in which signals are
not presently capable of being communicated between the components
over a conductive path to a closed-circuit relationship between
components in which signals can be communicated between components
over the conductive path. When a component, such as a controller,
couples other components together, the component initiates a change
that allows signals to flow between the other components over a
conductive path that previously did not permit signals to flow.
[0179] The term "isolated" refers to a relationship between
components in which signals are not presently capable of flowing
between the components. Components are isolated from each other if
there is an open circuit between them. For example, two components
separated by a switch that is positioned between the components are
isolated from each other when the switch is open. When a controller
isolates two components from one another, the controller affects a
change that prevents signals from flowing between the components
using a conductive path that previously permitted signals to
flow.
[0180] As used herein, the term "substantially" means that the
modified characteristic (e.g., a verb or adjective modified by the
term substantially) need not be absolute but is close enough to
achieve the advantages of the characteristic.
[0181] As used herein, the term "electrode" may refer to an
electrical conductor, and in some cases, may be employed as an
electrical contact to a memory cell or other component of a memory
array. An electrode may include a trace, wire, conductive line,
conductive layer, or the like that provides a conductive path
between elements or components of memory array.
[0182] As used herein, the term "shorting" refers to a relationship
between components in which a conductive path is established
between the components via the activation of a single intermediary
component between the two components in question. For example, a
first component shorted to a second component may exchange signals
with the second component when a switch between the two components
is closed. Thus, shorting may be a dynamic operation that enables
the flow of charge between components (or lines) that are in
electronic communication.
[0183] The devices discussed herein, including a memory array, may
be formed on a semiconductor substrate, such as silicon, germanium,
silicon-germanium alloy, gallium arsenide, gallium nitride, etc. In
some cases, the substrate is a semiconductor wafer. In other cases,
the substrate may be a silicon-on-insulator (SOI) substrate, such
as silicon-on-glass (SOG) or silicon-on-sapphire (SOP), or
epitaxial layers of semiconductor materials on another substrate.
The conductivity of the substrate, or sub-regions of the substrate,
may be controlled through doping using various chemical species
including, but not limited to, phosphorous, boron, or arsenic.
Doping may be performed during the initial formation or growth of
the substrate, by ion-implantation, or by any other doping
means.
[0184] A switching component or a transistor discussed herein may
represent a field-effect transistor (FET) and comprise a three
terminal device including a source, drain, and gate. The terminals
may be connected to other electronic elements through conductive
materials, e.g., metals. The source and drain may be conductive and
may comprise a heavily-doped, e.g., degenerate, semiconductor
region. The source and drain may be separated by a lightly-doped
semiconductor region or channel. If the channel is n-type (i.e.,
majority carriers are electrons), then the FET may be referred to
as a n-type FET. If the channel is p-type (i.e., majority carriers
are holes), then the FET may be referred to as a p-type FET. The
channel may be capped by an insulating gate oxide. The channel
conductivity may be controlled by applying a voltage to the gate.
For example, applying a positive voltage or negative voltage to an
n-type FET or a p-type FET, respectively, may result in the channel
becoming conductive. A transistor may be "on" or "activated" when a
voltage greater than or equal to the transistor's threshold voltage
is applied to the transistor gate. The transistor may be "off" or
"deactivated" when a voltage less than the transistor's threshold
voltage is applied to the transistor gate.
[0185] The description set forth herein, in connection with the
appended drawings, describes example configurations and does not
represent all the examples that may be implemented or that are
within the scope of the claims. The term "exemplary" used herein
means "serving as an example, instance, or illustration," and not
"preferred" or "advantageous over other examples." The detailed
description includes specific details to providing an understanding
of the described techniques. These techniques, however, may be
practiced without these specific details. In some instances,
well-known structures and devices are shown in block diagram form
to avoid obscuring the concepts of the described examples.
[0186] In the appended figures, similar components or features may
have the same reference label. Further, various components of the
same type may be distinguished by following the reference label by
a dash and a second label that distinguishes among the similar
components. If just the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
[0187] Information and signals described herein may be represented
using any of a variety of different technologies and techniques.
For example, data, instructions, commands, information, signals,
bits, symbols, and chips that may be referenced throughout the
above description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof.
[0188] The various illustrative blocks and modules described in
connection with the disclosure herein may be implemented or
performed with a general-purpose processor, a DSP, an ASIC, an FPGA
or other programmable logic device, discrete gate or transistor
logic, discrete hardware components, or any combination thereof
designed to perform the functions described herein. A
general-purpose processor may be a microprocessor, but in the
alternative, the processor may be any processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices (e.g., a
combination of a DSP and a microprocessor, multiple
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration).
[0189] The functions described herein may be implemented in
hardware, software executed by a processor, firmware, or any
combination thereof. If implemented in software executed by a
processor, the functions may be stored on or transmitted over as
one or more instructions or code on a computer-readable medium.
Other examples and implementations are within the scope of the
disclosure and appended claims. For example, due to the nature of
software, functions described above can be implemented using
software executed by a processor, hardware, firmware, hardwiring,
or combinations of any of these. Features implementing functions
may also be physically located at various positions, including
being distributed such that portions of functions are implemented
at different physical locations. Also, as used herein, including in
the claims, "or" as used in a list of items (for example, a list of
items prefaced by a phrase such as "at least one of" or "one or
more of") indicates an inclusive list such that, for example, a
list of at least one of A, B, or C means A or B or C or AB or AC or
BC or ABC (i.e., A and B and C). Also, as used herein, the phrase
"based on" shall not be construed as a reference to a closed set of
conditions. For example, an exemplary step that is described as
"based on condition A" may be based on both a condition A and a
condition B without departing from the scope of the present
disclosure. In other words, as used herein, the phrase "based on"
shall be construed in the same manner as the phrase "based at least
in part on."
[0190] Computer-readable media includes both non-transitory
computer storage media and communication media including any medium
that facilitates transfer of a computer program from one place to
another. A non-transitory storage medium may be any available
medium that can be accessed by a general purpose or special purpose
computer. By way of example, and not limitation, non-transitory
computer-readable media can comprise RAM, ROM, electrically
erasable programmable read only memory (EEPROM), compact disk (CD)
ROM or other optical disk storage, magnetic disk storage or other
magnetic storage devices, or any other non-transitory medium that
can be used to carry or store desired program code means in the
form of instructions or data structures and that can be accessed by
a general-purpose or special-purpose computer, or a general-purpose
or special-purpose processor. Also, any connection is properly
termed a computer-readable medium. For example, if the software is
transmitted from a website, server, or other remote source using a
coaxial cable, fiber optic cable, twisted pair, digital subscriber
line (DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
digital subscriber line (DSL), or wireless technologies such as
infrared, radio, and microwave are included in the definition of
medium. Disk and disc, as used herein, include CD, laser disc,
optical disc, digital versatile disc (DVD), floppy disk and Blu-ray
disc where disks usually reproduce data magnetically, while discs
reproduce data optically with lasers. Combinations of the above are
also included within the scope of computer-readable media.
[0191] The description herein is provided to enable a person
skilled in the art to make or use the disclosure. Various
modifications to the disclosure will be apparent to those skilled
in the art, and the generic principles defined herein may be
applied to other variations without departing from the scope of the
disclosure. Thus, the disclosure is not limited to the examples and
designs described herein but is to be accorded the broadest scope
consistent with the principles and novel features disclosed
herein.
* * * * *