U.S. patent application number 16/690285 was filed with the patent office on 2021-05-27 for look-ahead column sensing for fast voltage-mode read in ultrasonic sensors.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Subbarao Surendra CHAKKIRALA, Sameer WADHWA, Mowen YANG.
Application Number | 20210158001 16/690285 |
Document ID | / |
Family ID | 1000005579942 |
Filed Date | 2021-05-27 |
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United States Patent
Application |
20210158001 |
Kind Code |
A1 |
WADHWA; Sameer ; et
al. |
May 27, 2021 |
LOOK-AHEAD COLUMN SENSING FOR FAST VOLTAGE-MODE READ IN ULTRASONIC
SENSORS
Abstract
Certain aspects of the present disclosure provide techniques for
look-ahead column sensing for fast voltage-mode read on ultrasonic
sensors. For example, certain aspects are directed to an ultrasonic
sensor that generally includes a column line, a pixel having a
transistor coupled between a voltage rail and the column line, a
receiver circuit, and a first column control circuit coupled
between the receiver circuit and the pixel, the first column
control circuit being configured to electrically isolate the column
line from the receiver circuit during a look-ahead settling phase
of the ultrasonic sensor, and electrically couple the column line
to the receiver circuit during a sensing phase of the ultrasonic
sensor.
Inventors: |
WADHWA; Sameer; (San Diego,
CA) ; CHAKKIRALA; Subbarao Surendra; (San Jose,
CA) ; YANG; Mowen; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
1000005579942 |
Appl. No.: |
16/690285 |
Filed: |
November 21, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 9/0002 20130101;
G01N 29/22 20130101; G06K 9/0008 20130101 |
International
Class: |
G06K 9/00 20060101
G06K009/00 |
Claims
1. An ultrasonic sensor comprising: a column line; a pixel having a
first transistor coupled between a voltage rail and the column
line; a receiver circuit; and a first column control circuit
coupled between the receiver circuit and the pixel, the first
column control circuit being configured to: electrically isolate
the column line from the receiver circuit during a look-ahead
settling phase of the ultrasonic sensor; and electrically couple
the column line to the receiver circuit during a sensing phase of
the ultrasonic sensor.
2. The ultrasonic sensor of claim 1, wherein the first column
control circuit comprises: a second transistor having a gate
coupled to the column line; and a switch coupled between a source
of the second transistor and the receiver circuit.
3. The ultrasonic sensor of claim 2, wherein the first column
control circuit is configured to electrically isolate the column
line from the receiver circuit by opening the switch, and wherein
the first column control circuit is configured to electrically
couple the column line to the receiver circuit by closing the
switch during the sensing phase.
4. The ultrasonic sensor of claim 2, wherein the first column
control circuit further comprises a current mirror having a first
branch coupled between the voltage rail and a drain of the second
transistor and having a second branch coupled between the voltage
rail and a source of the second transistor, the switch being
coupled between the source of the second transistor and the
receiver circuit.
5. The ultrasonic sensor of claim 2, wherein the sensing phase
comprises a voltage-mode sensing phase.
6. The ultrasonic sensor of claim 5, wherein the first column
control circuit further comprises another switch coupled between
the column line and the receiver circuit, wherein the switch is
closed during the voltage-mode sensing phase, and wherein the other
switch is closed during a current-mode sensing phase of the
ultrasonic sensor.
7. The ultrasonic sensor of claim 1, wherein the pixel comprises a
switch coupled between the first transistor and the column line,
the switch being closed during the look-ahead settling phase and
the sensing phase.
8. The ultrasonic sensor of claim 1, further comprising a second
column control circuit having a second transistor and a resistive
element, the second transistor and the resistive element being
series coupled between the column line and a reference potential
node.
9. The ultrasonic sensor of claim 1, wherein the first transistor
is decoupled from the column line outside of the look-ahead
settling phase and the sensing phase.
10. The ultrasonic sensor of claim 1, wherein the ultrasonic sensor
is configured as a fingerprint sensor.
11. A method for ultrasonic sensing, comprising: receiving a sensor
signal at a gate of a transistor of a pixel of an ultrasonic
sensor, the transistor being coupled between a voltage rail and a
column line; electrically isolating the column line from a receiver
circuit during a look-ahead settling phase of the ultrasonic
sensor; and electrically coupling the column line to the receiver
circuit during a sensing phase of the ultrasonic sensor, the
sensing phase being after the look-ahead settling phase.
12. The method of claim 11, further comprising sensing a voltage at
the column line via another transistor having a gate coupled to the
column line, wherein coupling the column line to the receiver
circuit comprises closing a switch between a source of the other
transistor and the receiver circuit during the sensing phase.
13. The method of claim 12, wherein electrically isolating the
column line from the receiver circuit comprises opening the switch
during the look-ahead settling phase.
14. The method of claim 12, further comprising: generating a
current based on the sensed voltage; mirroring the generated
current; and providing a combination of the generated current and
the mirrored current to the receiver circuit during the sensing
phase.
15. The method of claim 12, further comprising closing another
switch coupled between the column line and the receiver circuit
during a current-mode sensing phase.
16. The method of claim 11, wherein the sensing phase comprises a
voltage-mode sensing phase.
17. The method of claim 11, further comprising closing a switch
coupled between the transistor and the column line during the
look-ahead settling phase and the sensing phase.
18. The method of claim 11, further comprising sinking a current
from the column line during the look-ahead settling phase.
19. The method of claim 11, further comprising decoupling the first
transistor from the column line outside of the look-ahead settling
phase and the sensing phase.
20. An apparatus for ultrasonic sensing, comprising: means for
receiving a sensor signal at a gate of a transistor of a pixel of
the apparatus, the transistor being coupled between a voltage rail
and a column line; means for electrically isolating the column line
from a receiver circuit during a look-ahead settling phase of the
apparatus; and means for electrically coupling the column line to
the receiver circuit during a sensing phase of the apparatus, the
sensing phase being after the look-ahead settling phase.
Description
BACKGROUND
Field of the Disclosure
[0001] Aspects of the present disclosure relate to sensors, and
more particularly, to ultrasonic sensors and techniques for
operating an ultrasonic sensor.
Description of Related Art
[0002] In an ultrasonic sensor system, an ultrasonic transmitter
may be used to send (e.g., during a transmission phase) an
ultrasonic wave through an ultrasonically transmissive medium or
media and towards an object to be detected. The transmitter may be
operatively coupled with an ultrasonic sensor (e.g., an ultrasonic
receiver) configured to detect (e.g., during a reception phase)
portions of the ultrasonic wave that are reflected from the
object.
[0003] In the context of an ultrasonic fingerprint imager, the
ultrasonic wave may travel through a platen on which a person's
finger may be placed to obtain a fingerprint image. After passing
through the platen, some portions of the ultrasonic wave encounter
skin that is in contact with the platen, e.g., fingerprint ridges,
while other portions of the ultrasonic wave encounter air, e.g.,
valleys between adjacent ridges of a fingerprint, and may be
reflected with different intensities back towards the ultrasonic
sensor. The ultrasonic reflected signals associated with the finger
may be processed and converted to a digital value representing the
signal strength of the reflected signal. For example, a
piezoelectric element may be used to convert the ultrasonic
reflection to an electric signal to be processed (e.g., amplified)
and sensed by a receiver circuit. When multiple such reflected
signals are collected over a distributed area, the digital values
of such signals may be used to produce a graphical display of the
signal strength over the distributed area, for example by
converting the digital values to an image, thereby producing an
image of the fingerprint. Thus, an ultrasonic sensor system may be
used as a fingerprint imager or other type of biometric
scanner.
SUMMARY
[0004] The systems, methods, and devices of the disclosure each
have several aspects, no single one of which is solely responsible
for its desirable attributes. Without limiting the scope of this
disclosure as expressed by the claims which follow, some features
will now be discussed briefly. After considering this discussion,
and particularly after reading the section entitled "Detailed
Description" one will understand how the features of this
disclosure provide advantages that include improved ultrasonic
sensing.
[0005] Certain aspects are directed to an ultrasonic sensor. The
ultrasonic sensor generally includes a column line, a pixel having
a transistor coupled between a voltage rail and the column line, a
receiver circuit, and a first column control circuit coupled
between the receiver circuit and the pixel. The first column
control circuit is configured to electrically isolate the column
line from the receiver circuit during a look-ahead settling phase
of the ultrasonic sensor and to electrically couple the column line
to the receiver circuit during a sensing phase of the ultrasonic
sensor.
[0006] Certain aspects are directed to a method for ultrasonic
sensing. The method generally includes receiving a sensor signal at
a gate of a transistor of a pixel of an ultrasonic sensor, the
transistor being coupled between a voltage rail and a column line,
electrically isolating the column line from a receiver circuit
during the look-ahead settling phase of the ultrasonic sensor, and
electrically coupling the column line to the receiver circuit
during a sensing phase of the ultrasonic sensor, the sensing phase
being after the look-ahead settling phase.
[0007] Certain aspects are directed to an apparatus for ultrasonic
sensing. The apparatus generally includes means for receiving a
sensor signal at a gate of a transistor of a pixel of the
apparatus, the transistor being coupled between a voltage rail and
a column line, means for electrically isolating the column line
from a receiver circuit during a look-ahead settling phase of the
apparatus, and means for electrically coupling the column line to
the receiver circuit during a sensing phase of the apparatus, the
sensing phase being after the look-ahead settling phase.
[0008] To the accomplishment of the foregoing and related ends, the
one or more aspects comprise the features hereinafter fully
described and particularly pointed out in the claims. The following
description and the appended drawings set forth in detail certain
illustrative features of the one or more aspects. These features
are indicative, however, of but a few of the various ways in which
the principles of various aspects may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the above-recited features of
the present disclosure can be understood in detail, a more
particular description, briefly summarized above, may be had by
reference to aspects, some of which are illustrated in the
drawings. It is to be noted, however, that the appended drawings
illustrate only certain typical aspects of this disclosure and are
therefore not to be considered limiting of its scope, for the
description may admit to other equally effective aspects.
[0010] FIG. 1 shows a diagrammatic representation of an example
mobile device that includes an ultrasonic sensing system according
to some implementations.
[0011] FIG. 2A shows a block diagram representation of components
of an example ultrasonic sensing system according to some
implementations.
[0012] FIG. 2B shows a block diagram representation of components
of an example mobile device that includes an ultrasonic sensing
system.
[0013] FIG. 3 illustrates a column line of a sensor array, in
accordance with certain aspects of the present disclosure.
[0014] FIG. 4 is a flow diagram illustrating example operations for
ultrasonic sensing, in accordance with certain aspects of the
present disclosure.
[0015] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one aspect may be beneficially utilized on other
aspects without specific recitation.
DETAILED DESCRIPTION
[0016] Various aspects of the disclosure are described more fully
hereinafter with reference to the accompanying drawings. This
disclosure may, however, be embodied in many different forms and
should not be construed as limited to any specific structure or
function presented throughout this disclosure. Rather, these
aspects are provided so that this disclosure will be thorough and
complete, and will fully convey the scope of the disclosure to
those skilled in the art. Based on the teachings herein one skilled
in the art should appreciate that the scope of the disclosure is
intended to cover any aspect of the disclosure disclosed herein,
whether implemented independently of or combined with any other
aspect of the disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the disclosure
is intended to cover such an apparatus or method which is practiced
using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the disclosure set forth herein. It should be understood that any
aspect of the disclosure disclosed herein may be embodied by one or
more elements of a claim.
[0017] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any aspect described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other aspects.
Example Mobile Device with Ultrasonic Sensor
[0018] FIG. 1 shows a diagrammatic representation of an example
mobile device 100 that includes an ultrasonic sensing system
according to some implementations. The mobile device 100 may be
representative of, for example, various portable computing devices
such as cellular phones, smartphones, multimedia devices, personal
gaming devices, tablet computers, and laptop computers, among other
types of portable computing devices. However, various
implementations described herein are not limited in application to
portable computing devices. Indeed, various techniques and
principles disclosed herein may be applied in traditionally
non-portable devices and systems, such as in computer monitors,
television displays, kiosks, vehicle navigation devices, and audio
systems, among other applications. Additionally, various
implementations described herein are not limited in application to
devices that include displays.
[0019] The mobile device 100 generally includes a housing (or
"case") 102 within which various circuits, sensors, and other
electrical components reside. In the illustrated example
implementation, the mobile device 100 also includes a touchscreen
display 104. The mobile device 100 may include various other
devices or components for interacting with, or otherwise
communicating information to or receiving information from, a user.
For example, the mobile device 100 may include one or more
microphones 106, one or more speakers 108, and in some cases one or
more at least partially mechanical buttons 110. The mobile device
100 may include various other components enabling additional
features such as, for example, one or more video or still-image
cameras 112, one or more wireless network interfaces 114 (for
example, Bluetooth, WiFi or cellular) and one or more non-wireless
interfaces 116 (for example, a universal serial bus (USB) interface
or a high-definition multimedia interface (HDMI) interface).
[0020] The mobile device 100 may include an ultrasonic sensing
system 118 capable of scanning and imaging an object signature,
such as a fingerprint, palm print, or handprint. In some
implementations, the ultrasonic sensing system 118 may function as
a touch-sensitive control button. In some implementations, a
touch-sensitive control button may be implemented with a mechanical
or electrical pressure-sensitive system that is positioned under or
otherwise integrated with the ultrasonic sensing system 118. In
other words, in some implementations, a region occupied by the
ultrasonic sensing system 118 may function both as a user input
button to control the mobile device 100 as well as a fingerprint
sensor to enable security features such as user authentication
features.
[0021] FIG. 2A shows a block diagram representation of components
of an example ultrasonic sensing system 200 according to some
implementations. As shown, the ultrasonic sensing system 200 may
include a sensor system 202 and a control system 204 electrically
coupled to the sensor system 202. The sensor system 202 may be
capable of scanning an object and providing raw measured image data
usable to obtain an object signature, for example, such as a
fingerprint of a human finger. The control system 204 may be
capable of controlling the sensor system 202 and processing the raw
measured image data received from the sensor system. In some
implementations, the ultrasonic sensing system 200 may include an
interface system 206 capable of transmitting or receiving data,
such as raw or processed measured image data, to or from various
components within or integrated with the ultrasonic sensing system
200 or, in some implementations, to or from various components,
devices, or other systems external to the ultrasonic sensing
system.
[0022] FIG. 2B shows a block diagram representation of components
of an example mobile device 210 that includes the ultrasonic
sensing system 200 of FIG. 2A. For example, the mobile device 210
may be a block diagram representation of the mobile device 100
shown in and described with reference to FIG. 1. The sensor system
202 of the ultrasonic sensing system 200 of the mobile device 210
may be implemented with an ultrasonic sensor array 212. The control
system 204 of the ultrasonic sensing system 200 may be implemented
with a controller 214 that is electrically coupled to the
ultrasonic sensor array 212. While the controller 214 is shown and
described as a single component, in some implementations, the
controller 214 may collectively refer to two or more distinct
control units or processing units in electrical communication with
one another.
[0023] The ultrasonic sensing system 200 of FIG. 2B may include an
image processing module 218. In some implementations, raw measured
image data provided by the ultrasonic sensor array 212 may be sent,
transmitted, communicated, or otherwise provided to the image
processing module 218. The image processing module 218 may include
any suitable combination of hardware, firmware, and software
configured, adapted, or otherwise operable to process the image
data provided by the ultrasonic sensor array 212. In some
implementations, the image processing module 218 may include signal
or image processing circuits or circuit components including, for
example, amplifiers (such as instrumentation amplifiers or buffer
amplifiers), analog or digital mixers or multipliers, switches,
analog-to-digital converters (ADCs), and/or passive or active
analog filters, among others.
[0024] In some implementations, in addition to the ultrasonic
sensing system 200, the mobile device 210 may include a separate
processor 220, a memory 222, an interface 216, and a power supply
224. In some implementations, the controller 214 of the ultrasonic
sensing system 200 may control the ultrasonic sensor array 212 and
the image processing module 218, and the processor 220 of the
mobile device 210 may control other components of the mobile device
210. In some implementations, the processor 220 communicates data
to the controller 214 including, for example, instructions or
commands. In some such implementations, the controller 214 may
communicate data to the processor 220 including, for example, raw
or processed image data.
[0025] Depending on the implementation, one or both of the
controller 214 and processor 220 may store data in the memory 222.
For example, the data stored in the memory 222 may include raw
measured image data, filtered image data, or otherwise processed
image data. The memory 222 may store processor-executable code or
other executable computer-readable instructions capable of
execution by one or both of the controller 214 and the processor
220 to perform various operations (or to cause other components
such as the ultrasonic sensor array 212, the image processing
module 218, or other modules to perform operations), including any
of the operations described herein.
[0026] In some implementations, the controller 214 or the processor
220 may communicate data stored in the memory 222 or data received
directly from the image processing module 218 through an interface
216 (e.g., corresponding to the interface system 206). For example,
such communicated data can include image data or data derived or
otherwise determined from image data. The interface 216 may
collectively refer to one or more interfaces of one or more various
types. In some implementations, the interface 216 may include a
memory interface for receiving data from or storing data to an
external memory such as a removable memory device. Additionally or
alternatively, the interface 216 may include one or more wireless
network interfaces or one or more wired network interfaces enabling
the transfer of raw or processed data to, as well as the reception
of data from, an external computing device, system or server. A
power supply 224 may provide power to some or all of the components
in the mobile device 210.
Example Techniques for Look-Ahead Column Sensing for Fast
Voltage-Mode Read in Ultrasonic Sensors
[0027] State-of-the-art thin-film-transistor (TFT) sensors may rely
on current-mode sensing to speed up ultrasonic sensing in the
presence of large parasitics. However, current-mode sensing is more
sensitive to system noise, as compared to voltage sensing, because
of a long high-impedance sense-node interface between the sensor
and receiver circuit (e.g., a receiver application specific
integrated-circuit (ASIC)). Voltage-mode sensing provides better
noise immunity as compared to current-mode sensing, but suffers
from slow sensing speed caused by relatively large parasitics.
Certain aspects of the present disclosure provide techniques for
speeding up voltage-mode sensing such that this sensing mode
matches (or is at least comparable to) current-mode sensing speed
while retaining noise rejection benefits associated with
voltage-mode sensing.
[0028] To increase the speed of voltage-mode sensing, TFT devices
may be used to drive the sense line (e.g., column line) parasitics,
such that the voltage at the column line of the ultrasonic sensor
settles before a sensing phase of the ultrasonic sensor begins. The
size of the ultrasonic sensor pixel circuitry may be relatively
small because of area constraints on various devices, limiting
signal drive capability in certain implementations. In certain
aspects of the present disclosure, the parasitics on the sense
lines may be split into two parts by using column buffers (e.g.,
also referred to as "column drivers") between portions of the sense
line. In this manner, pixel drive devices may only see the column
parasitics during a look-ahead sensing phase, while the column
drivers see the remaining parasitics on the sense lines, as
described in more detail herein. In other words, the voltage at the
columns of the sensor array may be settled in a look-ahead manner
where the columns predicted to be sensed next in sequence begin to
settle while previous columns are being sensed.
[0029] FIG. 3 illustrates a column line 301 of an ultrasonic sensor
array 300 (e.g., corresponding to the ultrasonic sensor array 212
described with respect to FIG. 2B), in accordance with certain
aspects of the present disclosure. As illustrated, the ultrasonic
sensor array 300 includes multiple columns, each selectively
coupled through respective buffers and switches (e.g., column
buffers and multiplexer 371) via sense lines to a receiver circuit
390 (e.g., a receiver (Rx) ASIC).
[0030] As illustrated, the column line 301 of the column 334 is
coupled to a pixel 336 having a transistor 338 (e.g., n-type
metal-oxide-semiconductor (NMOS) transistor). As used herein, a
pixel generally refers to circuitry associated with a portion of an
ultrasonic sensor array. The transistor 338 may be coupled to a
platen 393 for ultrasonic sensing. For example, an ultrasonic
signal may be received via the platen 393 and processed (e.g.,
converted to an electrical signal) via processing circuitry 395
(which may include a piezoelectric element, for example, among
other components).
[0031] In certain aspects, a switch 340 (e.g., implemented as an
NMOS transistor) may be coupled between the transistor 338 and the
column line 301. The switch 340 may be a row select switch of the
ultrasonic sensor array 300. The switch 340 may be closed during a
look-ahead settling phase and a sensing phase, and open outside the
look-ahead settling phase and the sensing phase. A column control
circuit 342 may be coupled to the column line 301 and may include a
transistor 344 and a resistive element 346. The transistor 344 and
the resistive element 346 may be series coupled between the column
line 301 and a reference potential node 399 (e.g., electric
ground). The transistor 338 may be biased to sink a current from
the column line 301 during a sensing phase (also referred to as a
"read phase") of the ultrasonic sensor array, as described in more
detail herein. The sensing phase may be implemented using
voltage-mode (VM) sensing (e.g. during a VM sensing phase), or
current-mode (CM) sensing (e.g., during a CM sensing phase), as
described in more detail herein.
[0032] The column control circuit 342 may also include a transistor
348 for resetting (e.g., discharging) the column line 301, for
example, after the sensing phase has completed. During the sensing
phase, a drain of the transistor 338 may be coupled to a voltage
rail Vdd, and the switch 340 may be closed. Thus, during the
sensing phase of the ultrasonic sensor array 300, the transistor
338 may be configured as a source follower, amplifying (e.g.,
buffering with a unity gain) a signal at a gate of the transistor
338. The amplified signal may be read by a receiver circuit 390
electrically coupled to the column line 301 during the sensing
phase. For example, when CM sensing is active, a CM column select
switch 370 may be closed, and the drain-to-source current (Ids) of
the transistor 338 may flow through the column line 301, across the
CM column select switch 370, to the receiver circuit 390 for
sensing.
[0033] When VM sensing is active, the CM column select switch 370
(Colsel_cm) may be opened, and the VM column select switch 372
(Colsel_vm) may be closed. As illustrated, the column control
circuit 380 includes a current mirror 382. A first branch 352 of
the current mirror 382 is coupled to a transistor 350. The
transistor 350 senses the voltage at the column line 301 at a gate
of the transistor 350, and sinks a current from the first branch
352 of the current mirror 382. The current sunk from the first
branch 352 of the current mirror 382 is mirrored at a second branch
354 of the current mirror. The currents from the first branch 352
and second branch 354 of the current mirror 382 are combined and
provided to the receiver circuit 390 for sensing. In certain
aspects, the column line 301 may include a parasitic element 392,
as illustrated by the example representative circuit of series
resistance and shunt capacitance.
[0034] Certain aspects of the present disclosure are directed to
techniques for look-ahead column sensing. For example, the
ultrasonic sensor array 300 includes multiple columns, one or more
of which may be undergoing sensing (e.g., during a sensing phase)
by a receiver circuit, while other columns may undergo look-ahead
settling (e.g., during a look-ahead settling phase). For instance,
during a first time instance 360, columns 302, 304, 306, 308 may be
undergoing sensing by the receiver circuit 390, while columns 310,
312, 314, 316 may be undergoing look-ahead settling. During a
following time instance 362, the columns 310, 312, 314, 316 that
were previously undergoing look-ahead settling may now undergo
sensing by the receiver circuit 390, while columns 318, 320, 322,
324 may undergo look-ahead settling. In a similar fashion, during a
following time instance 364, the columns 318, 320, 322, 324 that
were previously undergoing look-ahead settling may now undergo
sensing by the receiver circuit 390, while columns 326, 328, 330,
332 undergo look-ahead settling. While FIG. 3 illustrates four
columns undergoing sensing while four other columns are undergoing
look-ahead settling to facilitate understanding, the number of
columns undergoing look-ahead settling or sensing may be less than
or greater than four.
[0035] The look-ahead settling phase is used to settle parasitics
associated with a column line, as described in more detail herein.
For example, due to the parasitic element 392 of the column line
301, some latency may be associated with settling the voltage at
the column line 301 prior to sensing by the receiver circuit 390.
During the look-ahead settling phase, the voltage to be sensed at
the column line 301 may be settled, such that during the sensing
phase by the receiver circuit, any latency associated with settling
the voltage at the column line (e.g., settling the parasitics
associated with the column line) does not impact the sensing speed
of the receiver circuit during the sensing phase. For instance, as
described herein, a column control circuit 380 may be coupled to
the column line 301 and may include a CM column select switch 370
and a VM column select switch 372. During VM sensing, the CM column
select switch 370 is open, and the VM column select switch 372 is
closed. During the look-ahead settling phase, both the CM column
select switch 370 and the VM column select switch 372 may be open.
Moreover, the drain of the transistor 338 may be coupled to a
voltage rail Vdd, the row-select switch 340 may be closed, and the
transistor 344 may be biased, allowing the voltage at the column
line 301 to settle to a voltage level that is to be sensed later
during a sensing phase.
[0036] As described herein, during the voltage sensing phase, the
VM column select switch 372 is closed. The currents from the first
branch 352 and the second branch 354 of the current mirror 382 are
combined and provided to the receiver circuit 390 via one of sense
lines 379. As illustrated, the sense line may include a parasitic
element 378, an example of which is represented in FIG. 3 by series
resistive elements and a shunt capacitive element. Thus, during the
sensing phase, the latency associated with sensing the column line
voltage may be caused by settling the parasitic element 378, as
opposed to settling both the parasitic elements 392 and 378, since
the parasitic element 392 of the column line 301 was previously
settled during the look-ahead settling phase. Therefore, the
latency associated with reading a pixel during a sensing phase may
be less as compared to conventional implementations.
[0037] In certain aspects, at every read transition from one set of
pixels to the next, the coupling into the bias/column lines (e.g.,
the biasing of transistors 344) from low-to-high transitions may be
cancelled out by coupling from high-to-low transitions. For
example, a driver used to bias the transistor 344 may also drive
transistors of other pixels of the other columns of the ultrasonic
sensor. When the biasing signal of transistors of some of the
columns are transitioning from low to high (e.g., at the beginning
of a respective look-ahead sensing phase), the biasing signal of
other transistors of other columns are transitioning from high to
low (e.g., at the end of a respective sensing phase). Thus, slow
bias circuits and pixel driver devices in a TFT process are
unburdened from settling any alternating-current (AC) coupling and
may be designed to be low power and small in size. In certain
aspects, one or more dummy columns may be implemented at the edge
of the ultrasonic sensor array. The dummy column may be used for
dummy settling to mimic a look-ahead sensing phase at the edge of
the ultrasonic array.
[0038] FIG. 4 is a flow diagram illustrating example operations 400
for ultrasonic sensing, in accordance with certain aspects of the
present disclosure. The operations 400 may be performed, for
example, by an ultrasonic sensing system, which may include an
ultrasonic sensor array (e.g., such as the ultrasonic sensor array
300) and/or a controller such as the controller 214.
[0039] The operations 400 may begin, at block 405, by the
ultrasonic sensing system receiving a sensor signal at a gate of a
transistor (e.g., transistor 338) of a pixel (e.g., pixel 336) of
an ultrasonic sensor, the transistor being coupled between a
voltage (e.g., Vdd) and a column line (e.g., column line 301), and
at block 410, by electrically isolating (e.g., via switch 372) the
column line from a receiver circuit (e.g., receiver circuit 390)
during a look-ahead settling phase of the ultrasonic sensor. At
block 415, the ultrasonic sensing system may electrically couple
(e.g., via the switch 372) the column line to the receiver circuit
during a sensing phase of the ultrasonic sensor, the sensing phase
being after the look-ahead settling phase.
[0040] The operations 400 may also include sensing a voltage at the
column line via another transistor (e.g., transistor 350) having a
gate coupled to the column line, wherein coupling the column line
to the receiver circuit comprises closing a switch (e.g., switch
372) between a source of the other transistor and the receiver
circuit during the sensing phase. In certain aspects, electrically
isolating (i.e., electrically decoupling) the column line from the
receiver circuit may include opening the switch during the
look-ahead settling phase. In certain aspects, the operations 400
may also include the ultrasonic sensing system generating a current
(e.g., the drain-to-source current of transistor 350) based on the
sensed voltage, mirroring (e.g., via the current mirror 382) the
generated current, and providing a combination of the generated
current and the mirrored current to the receiver circuit during the
sensing phase.
[0041] In certain aspects, the sensing phase may include a
voltage-mode sensing phase. In certain aspects, the operations 400
may also include closing another switch (e.g., switch 370) coupled
between the column line and the receiver circuit during a
current-mode sensing phase.
[0042] In certain aspects, the operations 400 may also include
decoupling the first transistor from the column line outside of the
look-ahead settling phase and the sensing phase. In certain
aspects, the operations 400 may also include sinking (e.g., via the
column control circuit 342) a current from the column line during
the look-ahead settling phase.
[0043] The various operations of methods described above may be
performed by any suitable means capable of performing the
corresponding functions. The means may include various hardware
and/or software component(s) and/or module(s), including, but not
limited to a circuit, an application-specific integrated circuit
(ASIC), or processor. Generally, where there are operations
illustrated in figures, those operations may have corresponding
counterpart means-plus-function components with similar numbering.
In certain aspects, means for receiving may comprise processing
circuitry, such as the processing circuitry 395. Means for
electrically isolating and means for electrically coupling may
comprise a switch, such as the switch 370, which may be implemented
by a transistor, for example.
[0044] As used herein, the term "determining" encompasses a wide
variety of actions. For example, "determining" may include
calculating, computing, processing, deriving, investigating,
looking up (e.g., looking up in a table, a database, or another
data structure), ascertaining, and the like. Also, "determining"
may include receiving (e.g., receiving information), accessing
(e.g., accessing data in a memory), and the like. Also,
"determining" may include resolving, selecting, choosing,
establishing, and the like.
[0045] As used herein, a phrase referring to "at least one of" a
list of items refers to any combination of those items, including
single members. As an example, "at least one of: a, b, or c" is
intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as
any combination with multiples of the same element (e.g., a-a,
a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and
c-c-c or any other ordering of a, b, and c).
[0046] The various illustrative logical blocks, modules and
circuits described in connection with the present disclosure may be
implemented or performed with discrete hardware components designed
to perform the functions described herein. The methods disclosed
herein comprise one or more steps or actions for achieving the
described method. The method steps and/or actions may be
interchanged with one another without departing from the scope of
the claims. In other words, unless a specific order of steps or
actions is specified, the order and/or use of specific steps and/or
actions may be modified without departing from the scope of the
claims.
[0047] It is to be understood that the claims are not limited to
the precise configuration and components illustrated above. Various
modifications, changes, and variations may be made in the
arrangement, operation, and details of the methods and apparatus
described above without departing from the scope of the claims.
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