U.S. patent application number 15/653050 was filed with the patent office on 2018-08-23 for semiconductor device and method.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Huan-Neng Chen, Lan-Chou Cho, Chewn-Pu Jou, Feng Wei Kuo.
Application Number | 20180241345 15/653050 |
Document ID | / |
Family ID | 60420626 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180241345 |
Kind Code |
A9 |
Cho; Lan-Chou ; et
al. |
August 23, 2018 |
Semiconductor Device and Method
Abstract
A circuit includes a first digital controlled oscillator and a
second digital controlled oscillator coupled to the first digital
controlled oscillator. A skew detector is connected to determine a
skew between outputs of the first digital controlled oscillator and
the second digital controlled oscillator, and a decoder is utilized
to output a control signal, based on the skew, to modify a
frequency of the first digital controlled oscillator using a
switched capacitor array to reduce or eliminate the skew. A
differential pulse injection oscillator circuit and a pulse
injection signal generator circuit are also provided,
Inventors: |
Cho; Lan-Chou; (Hsinchu,
TW) ; Chen; Huan-Neng; (Taichung City, TW) ;
Jou; Chewn-Pu; (Hsinchu, TW) ; Kuo; Feng Wei;
(Zhudong Township, TW) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Company, Ltd. |
Hsinchu |
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TW |
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20170346444 A1 |
November 30, 2017 |
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Family ID: |
60420626 |
Appl. No.: |
15/653050 |
Filed: |
July 18, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15599694 |
May 19, 2017 |
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15653050 |
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15295298 |
Oct 17, 2016 |
9866173 |
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15599694 |
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14319787 |
Jun 30, 2014 |
9473152 |
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15295298 |
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14075021 |
Nov 8, 2013 |
9191014 |
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14319787 |
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62518991 |
Jun 13, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 27/288 20130101;
H03B 5/1243 20130101; H01F 38/14 20130101; H03B 5/08 20130101; H01F
27/2804 20130101; H03B 5/1228 20130101; H03K 3/36 20130101; H03L
7/24 20130101; H01F 19/04 20130101; H03L 7/099 20130101; H03L 7/00
20130101; H03L 7/087 20130101; H03K 3/86 20130101; H03B 2200/0074
20130101; H03B 5/1256 20130101; H03J 2200/10 20130101; H03B 5/1212
20130101; H03B 5/1296 20130101; H01F 5/04 20130101; H01F 27/2871
20130101 |
International
Class: |
H03B 5/12 20060101
H03B005/12; H03L 7/00 20060101 H03L007/00; H03B 5/08 20060101
H03B005/08; H01F 5/04 20060101 H01F005/04; H01F 38/14 20060101
H01F038/14; H01F 27/28 20060101 H01F027/28; H01F 19/04 20060101
H01F019/04 |
Claims
1. An integrated circuit, comprising: an LC tank oscillator
circuit; a positive pulse injector connected to a first output node
of the LC tank oscillator circuit, the positive pulse injector
configured to inject a positive reference signal into the LC tank
oscillator circuit; and a negative pulse injector connected to a
second output node of the LC tank oscillator circuit, the negative
pulse injector configured to inject a negative reference signal
into the LC tank oscillator circuit, wherein the negative reference
signal is an inverse of the positive reference signal.
2. The integrated circuit according to claim 1, wherein the LC tank
oscillator circuit comprises: a first inductor; a second inductor;
a capacitor; and an active feedback device.
3. The integrated circuit according to claim 2, wherein the first
inductor is connected to the first output node, the second inductor
is connected to the second output node, and the capacitor is
connected between the first output node and the second output
node.
4. The integrated circuit according to claim 2, wherein the active
feedback device is connected to a supply voltage.
5. The integrated circuit according to claim 2, wherein the active
feedback device is connected to a ground node.
6. The integrated circuit according to claim 1, wherein the
positive pulse injector comprises a Negative Metal Oxide
Semiconductor (NMOS) transistor and the negative pulse injector
comprises a Positive Metal Oxide Semiconductor (PMOS)
transistor.
7. The integrated circuit according to claim 6, wherein the NMOS
transistor comprises a drain terminal connected to the first output
node, a gate terminal connected to the positive reference signal,
and a source terminal connected to a ground node; and wherein the
PMOS transistor comprises a source terminal connected to a supply
voltage, a gate terminal connected to the negative reference
signal, and a drain terminal connected to the second output
node.
8. The integrated circuit according to claim 1, wherein the LC tank
oscillator circuit comprises: an inductor and a capacitor connected
in parallel; a first active feedback device connected to a supply
voltage; and a second active feedback device connected to a ground
node.
9. An integrated circuit, comprising: a signal generator; a first
inverter connected to the signal generator through a first coupling
capacitor; a reference signal generating circuit connected to the
signal generator through a second coupling capacitor, the reference
signal generating signal being configured to generate a reference
signal; a pull down block, comprising one or more pull down
branches, wherein each pull down branch of the one or more pull
down branches is connected to an output of the first inverter and
to one or more programmable input signals, and wherein each pull
down branch is configured to adjust a voltage threshold of the
first inverter in response to the one or more programmable input
signals to which the respective pull down branch is connected being
activated; a second inverter, wherein an input of the second
inverter is connected to the output of the first inverter; a first
comparator, configured to compare an output of the second inverter
to the reference signal to generate a pulse signal.
10. The integrated circuit according to claim 9, wherein the signal
generator is configured to generate a sinusoidal signal, and
wherein the first inverter outputs a square wave signal.
11. The integrated circuit according to claim 9, wherein the
reference signal generating circuit comprises a plurality of
inverters.
12. The integrated circuit according to claim 9, wherein a width of
the pulses of the pulse signal correspond to the voltage threshold
of the first inverter.
13. The integrated circuit according to claim 9, further
comprising: a second comparator, wherein the pulse signal is
connected to an input of the second comparator.
14. The integrated circuit according to claim 9, wherein each pull
down branch of the one or more pull down branches comprises: a
first transistor; and a second transistor; wherein the first
transistor has a control terminal connected to an input of the
first inverter; and wherein the second transistor has a control
terminal connected to one of the one or more programmable input
signals.
15. The integrated circuit according to claim 9, wherein the first
comparator is an AND gate.
16. The integrated circuit according to claim 9, wherein the first
inverter comprises a resistor connected between an input of the
inverter and the output of the inverter.
17. A method, comprising: generating, by a signal generator, a
sinusoidal signal; adjusting, by one or more programmable pull down
branches, a voltage threshold of a first inverter; generating, by
the first inverter, a first signal using the sinusoidal signal,
wherein the first signal is a square wave signal alternating
between a low value and a high value, and wherein a time duration
of the low values of the first signal depend at least in part on
the adjusted voltage threshold of the first inverter; generating a
second signal by inverting the first signal; generating a first
reference signal; and generating a first pulse signal by comparing
the second signal and the first reference signal.
18. The method according to claim 17, wherein adjusting the voltage
threshold of the first inverter comprises: activating, by one or
more control signals, a set of the one or more programmable pull
down branches, the set comprising a quantity of the one or more
programmable pull down branches, the quantity being in a range of 1
to 5; wherein a magnitude of the adjustment of the voltage
threshold of the first inverter is determined according the
quantity of the one or more programmable pull down branches.
19. The method according to claim 17, wherein generating the first
reference signal comprises: inverting the sinusoidal signal to
generate a third signal; inverting the third signal to obtain a
fourth signal; and inverting the fourth signal to obtain the first
reference signal.
20. The method according to claim 17, further comprising:
generating a second reference signal using the first reference
signal; and comparing the first pulse signal to the second
reference signal to generate a second pulse signal.
Description
PRIORITY CLAIM AND CROSS-REFERENCE
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 15/599,694, entitled "Semiconductor Device and
Method," filed on May 19, 2017, which application is a
continuation-in-part of U.S. application Ser. No. 15/295,298,
entitled "Coupling Structure for Inductive Device, filed on Oct.
17, 2016, which application is a continuation of U.S. patent
application Ser. No. 14/319,787, entitled "Coupling Structure for
Inductive Device," filed on Jun. 30, 2014, now U.S. Pat. No.
9,473,152 issued on Oct. 18, 2016, which application is a
continuation-in-part of U.S. patent application Ser. No.
14/075,021, entitled "Method and Apparatus of Synchronizing
Oscillators," filed on Nov. 8, 2013, now U.S. Pat. No. 9,191,014
issued on Nov. 17, 2015, which applications are incorporated herein
by reference.
BACKGROUND
[0002] In an integrated circuit, a clock tree is generally used for
distributing a common clock signal to various components in order
to synchronize the operation thereof. Differences in the arrival
time of the clock signals at two or more clocked components of the
integrated circuit can result in errors in the operation of the
integrated circuit. In some applications, the clock tree for the
distribution of the common clock signal includes structures such as
H-tree meshes or balanced buffer trees. In many cases, mismatch of
the arrival of the distributed clock signals is minimized at the
cost of sufficient driving current for distributing the common
clock signal along the clock tree. With the increase of the
frequency of the clock signal, power consumption for driving the
clock tree increases. Also, clock buffers at various stages of the
clock trees usually draw huge currents from a power supply grid,
and thus affect the performance of nearby components by causing
voltage drops of the supply voltage. In some applications, clock
trees use 20% to 40% of total power consumption of the integrated
circuits.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] One or more embodiments are illustrated by way of example,
and not by limitation, in the figures of the accompanying drawings,
wherein elements having the same reference numeral designations
represent like elements throughout.
[0004] FIG. 1 is a schematic diagram of two oscillators in
accordance with one or more embodiments.
[0005] FIG. 2A is a schematic diagram of a capacitor array usable
in one or both of the oscillators in FIG. 1 in accordance with one
or more embodiments.
[0006] FIG. 2B is a schematic diagram of a varactor usable in one
or both of the oscillators in FIG. 1 in accordance with one or more
embodiments.
[0007] FIG. 3 is a schematic diagram of six oscillators in
accordance with one or more embodiments.
[0008] FIG. 4 is a functional block diagram of a set of
master-slave fine-tuning unit in accordance with one or more
embodiments.
[0009] FIG. 5 is a schematic diagram of a pulse distribution
network in accordance with one or more embodiments.
[0010] FIG. 6 is a flowchart of a method of synchronizing
oscillators in accordance with one or more embodiments.
[0011] FIG. 7 is a schematic diagram of a ring oscillator in
accordance with one or more embodiments.
[0012] FIG. 8 is a schematic diagram of another ring oscillator in
accordance with one or more embodiments.
[0013] FIG. 9 is a top view of a coupling structure and
corresponding inductive devices in accordance with one or more
embodiments.
[0014] FIG. 10 is a diagram of coupling factor versus frequency
between two inductive devices, with or without a coupling
structure, in accordance with one or more embodiments.
[0015] FIGS. 11A-C are top views of coupling structures and
corresponding inductive devices in accordance with one or more
embodiments.
[0016] FIGS. 12A-E are top views of coupling structures and
corresponding inductive devices in accordance with one or more
embodiments.
[0017] FIGS. 13A-B are top views of coupling structures and
corresponding inductive devices in accordance with one or more
embodiments.
[0018] FIG. 14 is a top view of a coupling structure and
corresponding inductive devices in accordance with one or more
embodiments.
[0019] FIG. 15 is a top view of a coupling structure with shielding
structures and corresponding inductive devices in accordance with
one or more embodiments.
[0020] FIG. 16 is a flowchart of a method of magnetically coupling
inductive devices in accordance with one or more embodiments.
[0021] FIG. 17 is a clock distribution network in accordance with
one or more embodiments.
[0022] FIG. 18A-18B are views of coupled digital oscillators in
accordance with one or more embodiments.
[0023] FIG. 19 is a calibration system in accordance with one or
more embodiments.
[0024] FIG. 20 is a digital controlled oscillator in accordance
with one or more embodiments.
[0025] FIG. 21 is a switched capacitor in accordance with one or
more embodiments.
[0026] FIG. 22 is a model of the digital controlled oscillator in
accordance with one or more embodiments.
[0027] FIG. 23 is another digital controlled oscillator in
accordance with one or more embodiments.
[0028] FIG. 24 is another digital controlled oscillator in
accordance with one or more embodiments.
[0029] FIG. 25 is an oscillator in accordance with one or more
embodiments.
[0030] FIG. 26 is an oscillator in accordance with one or more
embodiments.
[0031] FIG. 27 is an oscillator in accordance with one or more
embodiments.
[0032] FIG. 28 is a graph depicting pulse width vs frequency for an
oscillator in a common mode and a differential mode in accordance
with one or more embodiments.
[0033] FIG. 29 is a pulse signal generator in accordance with one
or more embodiments.
[0034] FIG. 30 is a pulse signal generator in accordance with one
or more embodiments.
[0035] FIG. 31 is a timing diagram for a pulse signal generator in
accordance with one or more embodiments.
[0036] FIG. 32 is a flow chart of a method in accordance with one
or more embodiments.
DETAILED DESCRIPTION
[0037] It is understood that the following disclosure provides one
or more different embodiments, or examples, for implementing
different features of the disclosure. Specific examples of
components and arrangements are described below to simplify the
present disclosure. These are, of course, examples and are not
intended to be limiting. In accordance with the standard practice
in the industry, various features in the drawings are not drawn to
scale and are used for illustration purposes only.
[0038] In some embodiments, two or more oscillators configured to
generated output oscillating signals having a predetermined
frequency, instead of using a clock tree, is utilized to distribute
a clock signals to various clocked components in an integrated
circuit. Furthermore, one or more synchronization mechanisms are
implemented to minimize frequency or phase differences among the
oscillating signals generated by the two or more oscillators. In
some embodiments, the one or more synchronization mechanisms
include magnetic coupling, master-slave fine-tuning, and pulse
injection.
[0039] FIG. 1 is a schematic diagram of two oscillators 100A and
100B in accordance with one or more embodiments. In some
embodiments, oscillators 100A and 100B are configured to generate
oscillating signals having a predetermined frequency. In some
embodiments, frequencies of oscillating signals from oscillators
100A and 100B are approximately the same but not exactly equal to
the predetermined frequency. Also, in some embodiments, phases of
oscillating signals from oscillators 100A and 100B are not exactly
synchronized. In some embodiments, synchronizing oscillators 100A
and 100B refers to minimizing the frequency or phase differences
between the oscillating signals from oscillators 100A and 100B.
Although only two oscillators 100A and 100B are illustrated in
conjunction with FIG. 1, the synchronization mechanisms illustrated
in this disclosure are applicable to two or more similarly
configured oscillators of a same integrated circuit.
[0040] Oscillator 100A includes an inductive device 110A, a
capacitive device 120A, an active feedback device 130A, a switch
device 140A, an output node 152A, and a complementary output node
154A. Inductive device 110A, capacitive device 120A, active
feedback device 130A, and switch device 140A are coupled between
output node 152A and complementary output node 154A.
[0041] Active feedback device 130A includes two N-type transistors
132A and 134A. Source terminals of transistors 132A and 134A are
coupled with ground reference node 162A. A drain terminal of
transistor 132A is coupled with node 152A and a gate terminal of
transistor 134A, and a drain terminal of transistor 134A is coupled
with node 154A and a gate terminal of transistor 132A. Active
feedback device 130A is configured to output a first output
oscillating signal at node 152A and a first complementary output
oscillating signal at node 154A. The first output oscillating
signal and the first complementary output oscillating signal have
the predetermined frequency determined according to electrical
characteristics of inductive device 110A and electrical
characteristics of the capacitive device 120A. In some embodiments,
if inductive device 110A has a inductance of L.sub.TOTAL and
capacitive device 120A has a capacitance of C.sub.TOTAL, the
predetermined frequency F.sub.OSC (in Hz) is determinable according
to the following equation:
F OSC = 1 2 .pi. L TOTAL C TOTAL ##EQU00001##
[0042] In some applications, oscillators having configurations
similar to oscillator 100A are also known as "LC tank oscillators."
In some embodiments, transistors 132A and 134A are P-type
transistors. In some embodiments, other types of active feedback
devices are also usable as active feedback device 130A.
[0043] Inductive device 110A includes inductor 112A and inductor
114A integratedly formed as a conductive coil. Inductor 112A is
coupled between node 152A and a supply reference node 164A, and
inductor 114A is coupled between node 154A and supply reference
node 164A.
[0044] Capacitive device 120A includes a coarse-tuning capacitor
122A and a fine-tuning capacitor 124A. In some embodiments,
capacitance of coarse-tuning capacitor 122A is set according to a
set of digital signals from bus 126A. In some embodiments, a
coarse-tuning capacitor 122A is replaced by a set of hard-wired
capacitors, and thus capacitance of coarse-tuning capacitor 122A is
fixed and bus 126A is thus omitted. In some embodiments,
capacitance of fine-tuning capacitor 124A is set according to an
analog signal from path 128A. In some embodiments, a resonant
frequency of oscillator 100A is adjustable by controlling
coarse-tuning capacitor 122A or fine-tuning capacitor 124A.
[0045] Switch device 140A is configured to set signals at nodes
152A and 154A at corresponding predetermined voltage levels when
switch device 140A is turned on. For example, when switch device
140A is turned on, node 152A and 154A are electrically coupled
together. Under this circumstance, transistors 132A and 134A and
inductors 112A and 114A function as a voltage divider, and signals
at node 152A and 154A are set at a voltage level determinable
according to impedance of transistors 132A and 134A and inductors
112A and 114A. In some embodiments, when switch device 140A is
turned on, signals at node 152A and 154A are set at about the
middle of voltage levels of the supply reference node 164A and
ground reference node 162A.
[0046] Switches device 140A is controlled by a signal on path 170A.
In some embodiments, the control signal on path 170A is a pulse
signal used to force the crossing-over of oscillating signals at
node 152A and 154A. Therefore, in the present application, switch
device 140A is also referred to as a reset device or a
pulse-injection device. In some embodiments, switch device 140A is
a transistor. In some embodiments, switch device 140A is a P-type
transistor, an N-type transistor, or a transmission gate. In some
embodiments, switch device 140A is omitted.
[0047] Oscillator 100B includes an inductive device 110B, a
capacitive device 120B, an active feedback device 130B, a switch
device 140B, an output node 152B, and a complementary output node
154B. Oscillator 100B and Oscillator 100A have substantially the
same configuration. Components of oscillator 100B similar to those
of oscillator 100A are given similar reference numbers, except the
corresponding suffixes are changed from `A` to `B`. Features and
functions of oscillator 100B are substantially similar to those
advanced above with regard to oscillator 100A, and detailed
description regarding oscillator 100B is thus not repeated.
[0048] In some embodiments, oscillator 100A and oscillator 100B are
on a same substrate, different substrates on a same package
substrate, different substrates of a stack of substrates, or
different substrates of a stack of dies. In some embodiments, a
power distribution network is implemented to cause supply reference
nodes 164A and 164B to have substantially a same supply voltage
level, and to cause ground reference nodes 162A and 162B to have
substantially a same ground reference level. In some embodiments,
digital signals on buses 126A and 126B have the same logic
values.
[0049] In some embodiments, signals on path 170A and path 170B are
provided by a signal distribution network based on a common signal.
In some embodiments, signals on path 170A and path 170B are
synchronized signals. In some embodiments, signals on path 170A and
path 170B are pulse signals. In some embodiments, the predetermined
frequency of output oscillating signals of oscillators 100A and
100B is an integer multiple of a frequency of signals on path 170A
and path 170B.
[0050] Furthermore, inductive device 110A of oscillator 100A and
inductive device 110B of oscillator 100B are magnetically coupled
(as depicted by dotted arrow 180). Magnetic coupling between
inductive device 110A and inductive device 110B refers to that
magnetic flux generated by operating inductive device 110A affects
operation of inductive device 110B, and vice versa. Similar to the
location where oscillators 100A and 100B are disposed, in some
embodiments, inductive device 110A and inductive device 110B are on
a same substrate, different substrates on a same package substrate,
different substrates of a stack of substrates, or different
substrates of a stack of dies. Inductive device 110A and inductive
device 110B are configured to attenuate out-of-phase components and
enhance in-phase component of oscillating signals at node 152A of
oscillator 100A and node 152B of oscillator 100B. As a result,
after oscillator 100A and oscillator 100B are enabled, output
oscillating signals at nodes 152A and 152B are eventually
stabilized to be in-phase oscillating signals. In other words,
inductive device 110A and inductive device 110B are configured to
synchronize oscillating signals generated by oscillator 100A and
oscillator 100B.
[0051] In some embodiments, inductive device 110A of oscillator
100A and inductive device 110B of oscillator 100B have a distance
equal to or less than a predetermined distance in order to cause
mutual-inductance sufficient to synchronize oscillator 100A and
oscillator 100B within a predetermined period of time. In some
embodiments, the predetermined distance is one half of a wavelength
of an electromagnetic wave having the predetermined frequency of
oscillating signals. In some embodiments, the predetermined
frequency of output oscillating signals ranges from 100 MHz to 20
GHz.
[0052] FIG. 2A is a schematic diagram of a capacitor array 200
usable as coarse-tuning capacitor 122A or coarse-tuning capacitor
122B in accordance with one or more embodiments. Capacitor array
200 includes a first node 202, a second node 204, K transistors
212-1 to 212-K, and 2K capacitors 222-1 to 222-K and 224-1 to
224-K, where K is a positive integer. First node 202 and second
node 204 are usable to be connected with the corresponding node
152A or node 154A, or to be connected with the corresponding node
152B or node 154B. Capacitors 222-1 to 222-K are coupled to first
node 202, capacitors 224-1 to 224-K are coupled to second node 204,
and transistors 212-1 to 212-K are coupled between corresponding
pairs of capacitors 222-1 to 222-K and 224-1 to 224-K. Transistors
212-1 to 212-K function as switches and controlled by control
signals B[0], B[1], to B[K-1].
[0053] In some embodiments, transistors 212-1 to 212-K are P-type
transistors or N-type transistors. In some embodiments, transistors
212-1 to 212-K are replaced by transmission gates or other types of
switches. In some embodiments, capacitors 222-1 to 222-K and 224-1
to 224-K are metal-oxide-metal capacitors or metal-insulator-metal
capacitors.
[0054] In some embodiments, total capacitance of each path,
including one of transistors 212-1 to 212-K, a corresponding
capacitor of capacitors 222-1 to 222-K, and a corresponding
capacitor of capacitors 224-1 to 224-K, has a same value. Under
these circumstances, control signals B[0:K-1] are coded in a unary
coding format. In some embodiments, total capacitance of each path
as defined above corresponds to one of 2.sup.0, 2.sup.1, . . .
2.sup.K-1 times of a predetermined unit capacitance value. Under
these alternative circumstances, control signals B[0:K-1] are coded
in a binary coding format.
[0055] FIG. 2B is a schematic diagram of a varactor 250 usable as
fine-tuning capacitor 124A or fine-tuning capacitor 124B in FIG. 1
in accordance with one or more embodiments. Varactor 250 includes a
first node 252, a second node 254, a control node 256, and
transistors 262 and 264. First node 252 and second node 254 are
usable to be coupled with a corresponding node 152A or node 154A,
or to be coupled with a corresponding node 152B or node 154B.
Transistor 262 has a drain terminal and a source terminal coupled
together with first node 252. Transistor 262 has a gate terminal
coupled to the control node 256. Transistor 264 has a drain
terminal and a source terminal coupled together with second node
254. Transistor 264 has a gate terminal coupled to the control node
256. Control node 256 is configured to receive an analog control
signal V.sub.CAP, such as a control signal on path 128A or 128B. A
total capacitance between nodes 252 and 254 is adjustable
responsive to a voltage level of control signal V.sub.CAP. In some
embodiments, transistors 262 and 264 are P-type transistors or
N-type transistors.
[0056] In FIG. 1, only two oscillators 100A and 100B are depicted.
However, in some embodiments, there are more than two oscillators
for generating clocks in an integrated circuit. Also, the inductive
device 110A or 110B of an oscillator 100A or 100B is capable of
magnetically coupled with more than two inductive devices of two or
more oscillators.
[0057] For example, FIG. 3 is a schematic diagram of six
oscillators 300A to 300F in accordance with one or more
embodiments. Oscillators 300A to 300F have a configuration similar
to oscillator 100A described above. Among other things, oscillators
300A to 300F have corresponding inductive devices 310A to 310F.
Other details of oscillators 300A to 300F are omitted.
[0058] As depicted in FIG. 3, inductive devices 310A and 310B are
magnetically coupled (dotted arrow 380A); inductive devices 310B
and 310C are magnetically coupled (dotted arrow 380B); inductive
devices 310D and 310E are magnetically coupled (dotted arrow 380C);
inductive devices 310E and 310F are magnetically coupled (dotted
arrow 380D); inductive devices 310A and 310D are magnetically
coupled (dotted arrow 380E); inductive devices 310B and 310E are
magnetically coupled (dotted arrow 380F); and inductive devices
310C and 310F are magnetically coupled (dotted arrow 380G). In this
embodiment, mutual-inductive coupling 380A to 380G are configured
to cause oscillators 300A to 300F to generate oscillating signals
having approximately a same predetermined frequency and
approximately the same phase.
[0059] In some embodiments, inductive devices 310A to 310F are
formed on a same substrate, different substrates on a same package
substrate, different substrates of a stack of substrates, or
different substrates of a stack of dies. In some embodiments,
distances between two of inductive devices 310A to 310F that
corresponds to one of magnetic coupling 380A to 380G is equal to or
less than one half of a wavelength of an electromagnetic wave
having the predetermined frequency. In some embodiments, the
predetermined frequency of output oscillating signals ranges from
100 MHz to 20 GHz.
[0060] FIG. 4 is a functional block diagram of a set of
master-slave fine-tuning unit 400 in accordance with one or more
embodiments. The set of master-slave fine-tuning unit 400 is
coupled to a mater oscillator 402 and a slave oscillator 404 and is
capable of controlling a resonant frequency of slave oscillator 404
based on comparing output oscillating signals of master oscillator
402 and the slave oscillator 404. In some embodiments, master
oscillator 402 corresponds to oscillator 100B in FIG. 1, slave
oscillator 404 corresponds to oscillator 100A, and resonant
frequency of slave oscillator 404 is adjustable by controlling
fine-tuning capacitor 124A.
[0061] The set of master-slave fine-tuning unit 400 includes a
first phase comparator 412, a second phase comparator 414, a
control unit 416, a first conductive path 422, a second conductive
path 424, a first frequency divider 432, and a second frequency
divider 434.
[0062] First frequency divider 432 is disposed adjacent to and
electrically coupled to master oscillator 402. First frequency
divider 432 is configured to receive an output oscillating signal
CLK_M from master oscillator 402 and to generate a reference signal
CLK_MR by frequency-dividing the output oscillating signal CLK_M by
a predetermined ratio N. In some embodiments, N is a positive
integer. In some embodiments, N ranges from 4 to 16. Second
frequency divider 434 is disposed adjacent to and electrically
coupled to slave oscillator 402. Second frequency divider 434 is
configured to receive an output oscillating signal CLK_S from slave
oscillator 404 and to generate a reference signal CLK_SR by
frequency-dividing the output oscillating signal CLK_S by the
predetermined ratio N.
[0063] In some embodiments, first frequency divider 432 and second
frequency divider 434 are omitted, and oscillating signals CLK_M
and CLK_S are used as reference signal CLK_MR and reference signal
CLK_SR.
[0064] First phase comparator 412 is disposed adjacent to the
master oscillator 402. Second phase comparator 414 is disposed
adjacent to the slave oscillator 404. First conductive path 422 and
second conductive path 424 are disposed between master oscillator
402 and slave oscillator 404. First phase comparator 412 is
configured to generate a first phase error signal 442 according to
reference signal CLK_MR from master oscillator 402 and a delayed
version CLK_SR' of reference signal CLK_SR from the slave
oscillator 404 transmitted through first conductive path 422.
Second phase comparator 422 is configured to generate a second
phase error signal 444 according to reference signal CLK_SR from
slave oscillator 404 and a delayed version CLK_MR' of reference
signal CLK_MR from the master oscillator 402 transmitted through
the second conductive path 424.
[0065] Control unit 416 is configured to generate a tuning signal
V.sub.TUNE to slave oscillator 404 according to first phase error
signal 442 and second phase error signal 444. In some embodiments,
tuning signal V.sub.TUNE is usable as analog control signal
V.sub.CAP of FIG. 2B or as analog control signal for adjusting
fine-tuning capacitor 124A carried by path 128A of FIG. 1.
[0066] FIG. 5 is a schematic diagram of a pulse distribution
network 500 in accordance with one or more embodiments. In some
embodiments, pulse distribution network 500 is usable to provide a
control signal to switch device 140A of oscillator 100A through
path 170A and a control signal to switch device 140B of oscillator
100B through path 170B.
[0067] Pulse distribution network 500 includes a pulse generator
510, a driver 520, and one or more conductive paths arranged to
have an H-tree configuration. Two or more oscillators 532 and 534
are coupled to two of ends of the H-tree. In some embodiments,
oscillator 532 corresponds to oscillator 100A in FIG. 1, and
oscillator 532 corresponds to oscillator 100B.
[0068] Pulse generator 510 is configured to generate a pulse signal
usable as control signals for switch devices or reset devices of
corresponding oscillators. In some embodiments, the pulse signal
has a pulse frequency, and the predetermined frequency of output
oscillating signals of oscillators 532 and 534 is an integer
multiple of the pulse frequency. The pulse signal is transmitted to
oscillators 532 and 534 in order to set output oscillating signals
at predetermined voltage levels by corresponding switch devices of
the oscillators responsive to the pulse signal. Thus, a timing of
rising edges or falling edges of output oscillating signals of
oscillators 532 and 534 are synchronized according to the pulse
signal.
[0069] The H-tree depicted in FIG. 5 is a five-level H-tree
including one (2.sup.0) first level conductive path 541, two
(2.sup.1) second level conductive paths 543a and 543b coupled to
corresponding ends of path 541, four (2.sup.3) third level
conductive paths 545a, 545b, 545c, and 545d coupled to
corresponding ends of paths 543a or 543b, eight (2.sup.3) fourth
level conductive paths 547a to 547i coupled to corresponding ends
of paths 545a to 545d, and 16 (2.sup.4) fifth level conductive
paths 549a to 549p coupled to corresponding ends of paths 547a to
547i. Fifth level conductive paths 549a to 549p have ends connected
to corresponding switch devices of various oscillators. For
example, one end of path 549a is coupled to oscillator 532, and one
end of path 549b is coupled to oscillator 534. In some embodiments,
each ends of fifth level conductive paths 539a to 539p has a same
routing distance. Therefore, conductive paths from driver 520 to
corresponding ends of fifth level conductive paths 549a to 549p are
configured to impose substantially the same delay to the pulse
signal during the transmission and distribution thereof.
[0070] Driver 520 is configured to provide sufficient current
driving capability to transmit the pulse signal generated by pulse
generator 510 to various ends of the fifth level conductive paths
549a to 549p. In some embodiments, additional drivers 552, 554,
556, and 558 are at ends of second level conductive paths 543a and
543b. In some embodiments, additional drivers 552, 554, 556, and
558 are omitted. In some embodiments, additional drivers 552, 554,
556, and 558 are disposed at corresponding ends of a different
level of conductive paths in the H-tree.
[0071] Therefore, at least three different ways to synchronize
output oscillating signals of two or more oscillators, such as
oscillators 100A and 100B in FIG. 1, are described above: magnetic
coupling (illustrated with reference to FIGS. 1 and 3);
master-slave fine-tuning (illustrated with reference to FIG. 4);
and pulse injection (illustrated with reference to FIG. 5). In some
embodiments, two or more oscillators 100A and 100B are synchronized
using magnetic coupling and master-slave fine-tuning mechanisms. In
some embodiments, two or more oscillators 100A and 100B are
synchronized using magnetic coupling and pulse injection
mechanisms. In some embodiments, two or more oscillators 100A and
100B are synchronized using magnetic coupling, master-slave
fine-tuning, and pulse injection mechanisms.
[0072] FIG. 6 is a flowchart of a method 600 of synchronizing
oscillators, such as oscillators 100A and 100B depicted in FIG. 1,
in accordance with one or more embodiments. It is understood that
additional operations may be performed before, during, and/or after
the method 600 depicted in FIG. 6, and that some other processes
may only be briefly described herein.
[0073] In operation 610, oscillators are operated to output
oscillating signals. For example, in some embodiments, oscillator
100A is operated to output a first oscillating signal at node 152A,
and oscillator 100B is operated to output a second oscillating
signal at node 152B.
[0074] In operation 620, inductive devices of oscillators are
magnetically coupled. For example, in some embodiments, inductive
device 110A of oscillator 100A and inductive device 110B of
oscillator 100B are magnetically coupled in order to reduce a
frequency difference or phase difference between output oscillating
signals of oscillator 100A and oscillator 100B.
[0075] In operation 630, a pulse injection process is performed on
various oscillators. For example, in some embodiments, a pulse
injection process is performed on oscillator 100A and oscillator
100B. In some embodiments, operation 630 includes generating a
pulse signal (operation 632), transmitting the pulse signal to
switch device 140A of oscillator 100A through a first conductive
path, and transmitting the pulse signal to switch device 140B of
oscillator 100B through a second conductive path. In some
embodiments, the first conductive path and the second conductive
path are configured to impose substantially a same delay to the
pulse signal.
[0076] In some embodiments, operation 630 further includes setting
the first oscillating signal of oscillator 100A at a first
predetermined voltage level by switch device 140A responsive to the
pulse signal (operation 634), and setting the second oscillating
signal of oscillator 100B at a first predetermined voltage level by
switch device 140B responsive to the pulse signal (operation
636).
[0077] The method proceeds to operation 640, where a master-slave
fine-tuning process is performed on two or more oscillators. For
example, in some embodiments, a master-slave fine-tuning process is
performed on oscillator 100A and oscillator 100B. As depicted in
FIGS. 6 and 4, operation 640 includes generating reference signal
CLK_MR by frequency-dividing oscillating signal from oscillator 402
or 100B by a predetermined ratio (operation 642); and generating
reference signal CLK_SR by frequency-dividing oscillating signal
from oscillator 404 or 100A by the predetermined ratio (operation
643).
[0078] Furthermore, in operation 645, a first phase error signal
442 is generated based on reference signal CLK_MR and delayed
version CLK_SR' of reference signal CLK_SR transmitted through
conductive path 422. In operation 646, a second phase error signal
444 is generated based on reference signal CLK_SR and a delayed
version CLK_MR' of reference signal CLK_MR transmitted through
conductive path 424. In operation 648, a tuning signal V.sub.TUNE
is generated based on the first phase error signal 422 and the
second phase error signal 424.
[0079] As depicted in FIGS. 6 and 1, in operation 649, a frequency
or a phase of oscillating signal generated by oscillator 404 or
100A is adjusted based on the tuning signal V.sub.TUNE.
[0080] In some embodiments when synchronizing oscillators 100A and
100B of FIG. 1, either or both of operation 630 or operation 640
is/are omitted.
[0081] Moreover, the pulse distribution network 500 in FIG. 5 and
pulse-injection process (operation 630) are applicable to other
type of oscillators and not limited to LC tank oscillators. In some
embodiments, pulse-injection process or pulse-injection mechanism
described above is also applicable to a particular type of
oscillator known as ring oscillators.
[0082] For example, FIG. 7 is a schematic diagram of a ring
oscillator 700 in accordance with one or more embodiments.
Oscillator 700 has an output node 702 and P inverters 710-1 to
710-P, where P is an odd integer. Inverters 710-1 to 710-P are
connected in series. Furthermore, output terminal of the last stage
inverter 710-P is coupled with output node 702, and input terminal
of the first stage inverter 710-1 is coupled with output terminal
of inverter 710-P. Inverters 710-1 to 710-P are configured to be an
active feedback device and to generate an oscillating signal at
output node 702. Another inverter 720 has an input terminal
configured to receive a pulse signal and an output terminal coupled
with first node 702. Inverter 720 functions as a reset device
configured to set output oscillating signal at node 704 at a
predetermined voltage level responsive to the pulse signal. In some
embodiments, two or more ring oscillators similar to oscillator 700
(e.g., oscillators 532 and 534 in FIG. 5) are connected to various
ends of a pulse distribution network similar to pulse distribution
network 500 in order to synchronizing output oscillating signals of
the two or more ring oscillators.
[0083] FIG. 8 is a schematic diagram of another ring oscillator 800
in accordance with one or more embodiments. Oscillator 800 has a
pair of output nodes 802 and 804 and Q differential amplifiers
810-1 to 810-Q, where Q is an odd integer. Amplifiers 810-1 to
810-Q are connected in series. Output terminals of the last stage
amplifier 810-Q are coupled with output nodes 802 and 804, and
input terminals of the first stage amplifier 810-1 are coupled with
output terminals of amplifier 810-Q. Amplifiers 810-1 to 810-Q are
configured as an active feedback device and to generate a pair of
differential oscillating signals at output nodes 802 and 804. One
of the amplifiers, such as amplifier 810-1, further includes a
switch device or a reset device configured to set output terminals
of that amplifier 810-1 at a predetermined voltage level responsive
to a pulse signal. In some embodiments, any differential amplifier
among amplifiers 810-1 to 810-Q is usable for pulse signal
injection. In some embodiments, two or more ring oscillators
similar to oscillator 800 (e.g., oscillators 532 and 534 in FIG. 5)
are connected to various ends of a pulse distribution network
similar to pulse distribution network 500 in order to synchronizing
output oscillating signals of the two or more ring oscillators.
[0084] FIG. 9 is a top view of a portion of a circuit 900 including
a coupling structure 910 and corresponding first and second
inductive devices 922 and 924 in accordance with one or more
embodiments. In some embodiments, inductive devices 922 and 924
correspond to inductive devices 110A and 110B in FIG. 1 or
inductive devices 310A to 310F in FIG. 3. In some embodiments,
coupling structure 910 is configured to facilitate the magnetic
coupling 180 in FIG. 1 or magnetic coupling 308A to 380G in FIG.
3.
[0085] Coupling structure 910 includes a first conductive loop 912,
a second conductive loop 914, and a set of conductive paths 916
electrically connecting first conductive loop 912 and second
conductive loop 914. First conductive loop 912 and second
conductive loop 914 have a shape of an octagon loop. In some
embodiments, first conductive loop 912 and second conductive loop
914 have a shape of a polygon loop or a circular loop. First
conductive loop 912, second conductive loop 914, and the set of
conductive paths 916 are formed in various interconnection layers
of one or more chips. First conductive loop 912 surrounds the first
inductive device 922 as observed from a top view perspective.
Second conductive loop 914 surrounds the second inductive device
924 as observed from the top view perspective.
[0086] First inductive device 922 has a signal port 922a
corresponding to an opening of a coil of inductive device 922, a
center of the coil 922b, and a port direction 922c. Second
inductive device 924 has a signal port 924a corresponding to an
opening of a coil of inductive device 924, a center of the coil
924b, and a port direction 924c. In FIG. 10, port directions 922c
and 924c point to the same direction. In some embodiments, port
directions 922c and 924c point to different directions.
[0087] First conductive loop 912 includes a first end 912a and a
second end 912b. Second conductive loop 914 includes a first end
914a and a second end 914b. The set of conductive paths 916
includes a first conductive path 916a and a second conductive path
916b. First conductive path 916a electrically connects first end
912a of first conductive loop 912 and first end 914a of second
conductive loop 914. Second conductive path 916b electrically
connects second end 912b of first conductive loop 912 and second
end 914b of second conductive loop 914. A length L is defined as
the length of a space between first conductive loop 912 and second
conductive loop 914. In some embodiments, length L is equal to or
greater than 100 .mu.m.
[0088] In some embodiments, an induced current is generated at
first conductive loop 912 responsive to a first magnetic field
generated by first inductive device 922. The induced current is
transmitted to second conductive loop 914 through the set of
conductive paths 916 and generates a second magnetic field within
the second conductive loop 914. Accordingly, a mutual inductance
between the first and second inductive devices 922 and 924 is less
dependent from the field distribution of first magnetic field and
more dependent from the second magnetic field reproduced by the
induced current. As a result, a mutual inductance between the first
and second inductive devices 922 and 924 is independent of a
distance between inductive devices 922 and 924, such as when the
length L is equal to or greater than 100 .mu.m.
[0089] FIG. 10 is a diagram of coupling factor K versus frequency
Freq between two inductive devices, such as inductive devices 922
and 924, with or without a coupling structure, in accordance with
one or more embodiments. Curve 1010 represents a coupling factor K
between inductive devices 922 and 924 when there is no coupling
structure 910 and a distance therebetween is set to be 1000 .mu.m.
Curve 1020a represents a coupling factor K between inductive
devices 922 and 924, with coupling structure 910 and a length L set
to be 500 .mu.m; curve 1020b represents a coupling factor K if
length L is 1000 .mu.m; curve 1020c represents a coupling factor K
if length L is 2000 .mu.m; curve 1020d represents a coupling factor
K if length L is 3000 .mu.m; and curve 1020e represents a coupling
factor K if length L is 5000 .mu.m. Reference line 1030 represents
a K value of 0.001 (10.sup.-3).
[0090] Coupling factor K is defined as:
K = M L 1 L 2 ##EQU00002##
M is the mutual conductance between inductive devices 922 and 924,
L.sub.1 is the self-inductance of first inductive device 922, and
L.sub.2 is the self-inductance of first inductive device 924. If
the K value is greater than 0.001 (reference line 1030),
oscillators corresponding to inductive devices 922 and 924 have
meaningful magnetic coupling sufficient to maintain a stable phase
difference therebetween.
[0091] As shown by curve 1010 in FIG. 10, at a distance of 1000
.mu.m, a configuration without coupling structure 910 no longer
ensures sufficient magnetic coupling between inductive devices 922
and 924. In contrast, curves 1020a-1020e demonstrate that an
embodiment with coupling structure 910 renders the magnetic
coupling between inductive devices 922 and 924 independent of the
distance therebetween. As shown in FIG. 10, after 500 MHz, curves
1020a-1020e are all above reference line 1030 for length L set to
500, 1000, 2000, 3000, or 5000 .mu.m.
[0092] Some possible variations along the embodiment of FIG. 9 are
further illustrated in conjunction with FIGS. 11A-15. In some
embodiments, variations as illustrated in FIGS. 11A-15 are
combinable to form yet a different variation consistent with the
ideas as demonstrated in conjunction with FIG. 9 and FIGS.
11A-15.
[0093] FIG. 11A is a top view of a coupling structure 910A and
corresponding inductive devices 922 and 924 in accordance with one
or more embodiments. The components the same or similar to those in
FIG. 9 are given the same reference numbers, and detailed
description thereof is omitted.
[0094] Compared with coupling structure 910, coupling structure
910A includes a set of conductive paths 916A in place of the set of
conductive paths 916. The set of conductive paths 916A includes a
first conductive path 916Aa and a second conductive path 916Ab.
First conductive path 916Aa and second conductive path 916Ab are
routed such that first conductive path 916Aa crosses over second
conductive path 916Ab at location 1110 as observed from a top view
perspective.
[0095] FIG. 11B is a top view of a coupling structure 910B and
corresponding inductive devices 922 and 924 in accordance with one
or more embodiments. The components the same or similar to those in
FIG. 9 are given the same reference numbers, and detailed
description thereof is omitted.
[0096] Compared with coupling structure 910, coupling structure
910B includes a set of conductive paths 916B in place of the set of
conductive paths 916. The set of conductive paths 916B includes a
first conductive path 916Ba and a second conductive path 916Bb.
First conductive path 916Ba and second conductive path 916Bb are
routed such that each one of first conductive path 916Ba and second
conductive path 916Bb has an angled corner at location 1120 as
observed from a top view perspective.
[0097] FIG. 11C is a top view of a coupling structure 910C and
corresponding inductive devices 922 and 924 in accordance with one
or more embodiments. The components the same or similar to those in
FIG. 9 are given the same reference numbers, and detailed
description thereof is omitted.
[0098] Compared with coupling structure 910, coupling structure
910C includes a set of conductive paths 916C in place of the set of
conductive paths 916. The set of conductive paths 916C includes a
first conductive path 916Ca and a second conductive path 916Cb.
First conductive path 916Ca and second conductive path 916Cb are
routed such that each one of first conductive path 916Ca and second
conductive path 916Cb has an angled corner at location 1130 as
observed from a top view perspective. Also, first conductive path
916Ca crosses over second conductive path 916Cb at location 1130 as
observed from the top view perspective.
[0099] FIG. 12A is a top view of a coupling structure 1210A and
corresponding inductive devices 1222 and 1224 in accordance with
one or more embodiments. Coupling structure 1210A includes a first
conductive loop 1212A, a second conductive loop 1214A, a first set
of conductive paths 1216A electrically connecting conductive loops
1212A and 1214A, a third conductive loop 1212B, a fourth conductive
loop 1214B, and a second set of conductive paths 1216B electrically
connecting conductive loops 1212B and 1214B. A first inductive
device 1222 is magnetically coupled with first conductive loop
1212A. A second inductive device 1224 is magnetically coupled with
third conductive loop 1212B. Second conductive loop 1214A is
magnetically coupled with fourth conductive loop 1214B. Second
conductive loop 1214A surrounds fourth conductive loop 1214B as
observed from a top view perspective.
[0100] In some embodiments, a first induced current is generated at
first conductive loop 1212A responsive to a first magnetic field
generated by first inductive device 1222. The first induced current
is transmitted to second conductive loop 1214A through the first
set of conductive paths 1216A and generates a second magnetic field
within second conductive loop 1214A. A second induced current is
generated at fourth conductive loop 1214B responsive to the second
magnetic field. The second induced current is transmitted to third
conductive loop 1214B through the second set of conductive paths
1216B and generates a third magnetic field within third conductive
loop 1214B. Accordingly, second inductive device 1224 is
magnetically coupled with first inductive device 1222 through the
third magnetic field reproduced by the second induced current
within third conductive loop 1214B.
[0101] FIG. 12B is a top view of a coupling structure 1210B and
corresponding inductive devices 1222 and 1224 in accordance with
one or more embodiments. Components that are the same or similar to
those in FIG. 12A are given the same reference numbers, and
detailed description thereof is omitted. Compared with coupling
structure 1210A, second conductive loop 1214A and fourth conductive
loop 1214B overlap as observed from a top view perspective. In
other words, second conductive loop 1214A and fourth conductive
loop 1214B have the same size and shape but formed on different
interconnection layers.
[0102] FIG. 12C is a top view of a coupling structure 1210C and
corresponding inductive devices 1222, 1224, and 1226 in accordance
with one or more embodiments. Components that are the same or
similar to those in FIG. 12A are given the same reference numbers,
and detailed description thereof is omitted. Compared with coupling
structure 1210A, second conductive loop 1214A and fourth conductive
loop 1214B are arranged to magnetically couple with an additional
inductive device 1226. Also, fourth conductive loop 1214B surrounds
second conductive loop 1214A as observed from a top view
perspective.
[0103] FIG. 12D is a top view of a coupling structure 1210D and
corresponding inductive devices 1222, 1224, and 1226 in accordance
with one or more embodiments. Components that are the same or
similar to those in FIG. 12B are given the same reference numbers,
and detailed description thereof is omitted. Compared with coupling
structure 1210B, second conductive loop 1214A and fourth conductive
loop 1214B are arranged to magnetically couple with an additional
inductive device 1226.
[0104] FIG. 12E is a top view of a coupling structure 1210E and
corresponding inductive devices 1222, 1224, and 1226 in accordance
with one or more embodiments. Components that are the same or
similar to those in FIG. 12D are given the same reference numbers,
and detailed description thereof is omitted. Compared with coupling
structure 1210D, a set of conductive paths 1216B' is used in place
of second set of conductive paths 1216B, where one conductive path
of the set of conductive paths 1216B' crosses over another
conductive path of the set of conductive paths 1216B' at location
1230.
[0105] FIG. 13A is a top view of a coupling structure 1310A and
corresponding inductive devices 1322, 1324, and 1326 in accordance
with one or more embodiments. Coupling structure 1310A includes
three conductive loops 1312, 1314, and 1316 electrically coupled
together through a set of conductive paths 1318. Each one of
conductive loops 1312, 1314, and 1316 is magnetically coupled with
a corresponding one of inductive devices 1322, 1324, and 1326.
[0106] FIG. 13B is a top view of a coupling structure 1310B and
corresponding inductive devices 1322, 1324, 1326, and 1327 in
accordance with one or more embodiments. Components that are the
same or similar to those in FIG. 13A are given the same reference
numbers, and detailed description thereof is omitted. Coupling
structure 1310B includes four conductive loops 1312, 1314, 1316,
and 1317 electrically coupled together through a set of conductive
paths 1318. Each one of conductive loops 1312, 1314, 1316, and 1317
is magnetically coupled with a corresponding one of inductive
devices 1322, 1324, 1326, and 1327.
[0107] FIG. 14 is a top view of a coupling structure 1410 and
corresponding inductive devices 922 and 924 in accordance with one
or more embodiments. Components that are the same or similar to
those in FIG. 9 are given the same reference numbers, and detailed
description thereof is omitted. Coupling structure 1410 includes
two conductive loops 1412 and 1414 electrically coupled together
through a set of conductive paths 1416. Each one of conductive
loops 1412 and 1416 is magnetically coupled with a corresponding
one of inductive devices 922 and 924. Moreover, inductive device
922 surrounds conductive loop 1412 as observed from a top view
perspective; and inductive device 924 surrounds conductive loop
1414 as observed from the top view perspective.
[0108] FIG. 15 is a top view of a coupling structure 910 with
shielding structures 1512 and 1514 and corresponding inductive
devices 922 and 924 in accordance with one or more embodiments.
Components that are the same or similar to those in FIG. 9 are
given the same reference numbers, and detailed description thereof
is omitted. Compared with the circuit 900 in FIG. 9, the circuit
depicted in FIG. 15 further includes a first shielding structure
1512 and a second shielding structure 1514. At least a portion of
the set of conductive paths 916 is between first shielding
structure 1512 and second shielding structure 1514 as observed from
a top view perspective.
[0109] FIG. 16 is a flowchart of a method 1600 of magnetically
coupling inductive devices in accordance with one or more
embodiments. In some embodiments, method 1600 is usable in
conjunction with the circuit in FIG. 9 or FIG. 12A. In some
embodiments, method 1600 is also usable in conjunction with the
circuit in FIGS. 11A-11C, FIGS. 12B-12E, or FIGS. 13A-15. It is
understood that additional operations may be performed before,
during, and/or after the method 1600 depicted in FIG. 16, and that
some other processes may only be briefly described herein.
[0110] The process begins with operation 1610, where an induced
current is generated at a first conductive loop 912 or 1212A
responsive to a first magnetic field of a first oscillator
generated by a first inductive device 922 or 1222.
[0111] The process proceeds to operation 1620, where the induced
current is transmitted to a second conductive loop 914 or 1214A
through a set of conductive paths 916 or 1216A electrically
connecting the first and second conductive loops.
[0112] The process proceeds to operation 1630, where a second
magnetic field is generated responsive to the induced current
passing the second conductive loop 914 or 1214A.
[0113] For a coupling structure having a configuration the same or
similar to FIG. 12A or FIGS. 12B-E, the process proceeds to
operation 1640, where another induced current is generated at a
third conductive loop 1214B responsive to the second magnetic
field.
[0114] The process proceeds to operation 1650, where the another
induced current is transmitted to a fourth conductive loop 1212B
through another set of conductive paths 1216B electrically
connecting the third and fourth conductive loops.
[0115] As a result, a second inductive device 924 or 1224 of a
second oscillator is magnetically coupled with the first inductive
device 922 or 1222 of the first oscillator through the coupling
structure 910 or 1210.
[0116] FIG. 17 illustrates yet another embodiment in which coupled
oscillators may be utilized in order to supply clock signals
throughout a clock tree. In this embodiment, a clock distribution
network 1701, instead of using a single high speed clock to drive
the clock distribution network 1701, uses a low frequency reference
clock that is propagated through the distributive paths in order to
synchronize local digital controlled oscillators (DCOs) 1703. In an
embodiment the clock distribution network 1701 may be similar to
the pulse distribution network 500 described above with respect to
FIG. 5, and certain embodiments include a clock pulse generator
(not separately illustrated in FIG. 17), a clock driver 1705, and
one or more conductive paths arranged to have an H-tree
configuration and a power dissipation of C*V.sup.2*f. However, any
suitable configuration for the clock distribution network 1701 may
be utilized.
[0117] At the endpoints of the clock distribution network 1701
(e.g., at the endpoints of the H-trees), the digital controlled
oscillators 1703 are connected. In an embodiment the digital
controlled oscillators 1703 receive the low frequency reference
clock signal (from the clock driver 1705) and output a local
high-frequency clock signal to the remaining circuitry. In a
particular embodiment, the low frequency reference clock signal may
be propagated throughout the clock distribution network 1701 at a
frequency of between about 62.5 MHz and about 187.5 MHz, such as
about 125 MHz. Additionally, the digital controlled oscillators
1703 receive the low frequency reference clock as an input and
output the local high-frequency clock signal of between about 2 GHz
and about 6 GHz, such as about 4 GHz. However, any suitable
frequencies may be utilized.
[0118] Additionally, while the low frequency reference clock is
used to injection lock the digital controlled oscillators 1703 to
improve jitter performance, skew between the different local
high-frequency clock signals that are output from different ones of
the digital controlled oscillators 1703 (from, e.g., process,
supply, and temperature variations) may be reduced by coupling the
digital controlled oscillators 1703 together. In an embodiment the
separate digital controlled oscillators 1703 are coupled together
magnetically (as illustrated in FIG. 17 by the dashed lines labeled
1707). However, the digital controlled oscillators 1703 are not
limited to being coupled only magnetically. Rather, any suitable
method of coupling the oscillators, such as coupling the
oscillators through transmission lines, may also be utilized, and
all such coupling are fully intended to be included within the
scope of the embodiments.
[0119] FIGS. 18A and 18B illustrate a close up view of two of the
digital controlled oscillators 1703 within the dashed box 1711 in
FIG. 17. In this embodiment a first one of the digital controlled
oscillators 1703 is a master coupled oscillator which outputs a
first high frequency signal CKV. Additionally, a second one of the
digital controlled oscillators 1703 is a slave coupled oscillator
which outputs a second high frequency signal CKR. Ideally, the
first high frequency signal CKV and the second high frequency
signal CKR are identical, but without some form of phase
calibration, the first high frequency signal CKV and the second
high frequency signal CKR will be out of phase, having a phase
error .PHI..sub.error otherwise called skew.
[0120] FIG. 18B illustrates this phase error. In particular, when
two of the digital controlled oscillators 1703 are coupled e.g.,
through a transmission line 1803 (made of, for example,
polysilicon, a silicide, or a metal line) as illustrated or through
a magnetic coupling, the output frequency .omega..sub.0 of the
digital controlled oscillators 1703 will be identical. However,
there will also be a constant phase shift .DELTA.P between the
first high frequency signal CKV (e.g. clk.sub.2) and the second
high frequency signal CKR (e.g., clk.sub.1. Additionally, this
phase shift .DELTA.P will be proportional to the difference in the
natural frequencies .DELTA.f between the first digital controlled
oscillator 1703 and the second digital controlled oscillator 1703.
In particular embodiments, the relationship between the difference
in natural frequencies .DELTA.f is close to being linear to the
phase difference .DELTA.P in the signals being output by the
digital controlled oscillators 1703.
[0121] FIG. 19 illustrates a calibration system 1901 which uses
this relationship in the natural frequencies .DELTA.f to control
the phase shift .DELTA.P and calibrate the clock skew. In an
embodiment the calibration system 1901 comprises a skew detector
1905 and a decoder 1903 connected to the decoder 1903. In an
embodiment the first high frequency signal CKV and the second high
frequency signal CKR are both routed to a skew detector 101 as they
are also sent to the remainder of the circuitry. The skew detector
1905 may be used to receive the first high frequency signal CKV and
the second high frequency signal CKR and detect the phase error
.PHI..sub.error between the two signals. In a particular embodiment
the skew detector 1905 can be a time-digital converter (TDC), a
sample and hold d-type flip flop, a single d-type flip flop, or the
like. However, any suitable structure that can be used to detect
the phase error .PHI..sub.error between the first high frequency
signal CKV and the second high frequency signal CKR may be
utilized.
[0122] Once the phase error .PHI..sub.error between the first high
frequency signal CKV and the second high frequency signal CKR has
been determined by the skew detector 1905, the result of the phase
error .PHI..sub.error is then sent to a decoder 1903 where it can
be used to help control the natural frequency of the coupled
digital controlled oscillators 1703. For example, because the phase
error .PHI..sub.error is proportional to the difference in the
natural frequencies of the digital controlled oscillators 1703, the
resolution of the skew calibration is dominated by the resolution
of the digital controlled oscillators 1703. To help calibrate and
minimize the skew, the resolution of the digital controlled
oscillators 1703 may be made as high as practical.
[0123] To improve the resolution of the digital controlled
oscillators 1703, the overall inductance (L) of one of the digital
controlled oscillators 1703 is split into a plurality of individual
inductances. For example, in one embodiment the overall inductance
L of one of the digital controlled oscillators 1703 is split into a
first inductance of nL/2 and a second inductance of (1-n)L/2.
However, any suitable split in the overall inductance may be
utilized.
[0124] FIG. 20 illustrates an embodiment of an implementation of
this split of the overall inductance into the digital controlled
oscillators 1703. In one embodiment the digital controlled
oscillator 1703 comprises the active feedback device 130A
(described above with respect to FIG. 1), a first set of inductors
2003 (formed of, for example, polysilicon, silicide, or metal
lines), a second set of inductors 2005 (formed of, for example,
polysilicon, silicide, or metal lines), a first capacitor 2007, and
a switched capacitor array 2009 set within the middle of the
inductors. However, fewer structures or additional structures may
also be utilized.
[0125] In an embodiment the first set of inductors 2003 are
manufactured in order to provide (1-n)L/2 of the overall inductance
for the digital controlled oscillators 1703. In an embodiment there
may be two inductors of the first set of inductors 2003 provided in
parallel with each other (but separated by the first capacitor 2007
and the switched capacitor array 2009), although any suitable
number of individual inductors may be utilized.
[0126] The second set of inductors 2005 are manufactured in order
to provide nL/2 of the overall inductance for the digital
controlled oscillators 1703. In an embodiment there may be two
inductors of the second set of inductors 2005 provided in parallel
with each other (but separated by the switched capacitor array
2009). Additionally, individual ones of the second set of inductors
2005 are in series with individual ones of the first set of
inductors 2003.
[0127] The first capacitor 2007 is connected between the second set
of inductors 2005 and the active feedback device 130A. In an
embodiment the first capacitor 2007 may have a capacitance of
between about 0.1 pF and about 2 pF, such as about 1 pF. However,
any suitable capacitance may be utilized. Additionally, the first
capacitor 2007 is connected at a first node 2011 and a second node
2013 to the active feedback device 130A, and the first node and
second node may also be connected to either the output transmission
line or an output to another digital controlled oscillator.
[0128] The switched capacitor array 2009 is utilized to receive the
signals from the decoder 1903 (in FIG. 19) and to modify the
natural frequency of the digital controlled oscillator 1703 in
which it is located. In an embodiment the switched capacitor array
2009 comprises a plurality of switch capacitors 2100 and is located
in the middle of the first set of inductors 2003 and the second set
of inductors 2005. However, any suitable location may be
utilized.
[0129] FIG. 21 illustrates one embodiment of a structure formed
using NMOS structures that may be utilized as one of the switch
capacitors 2100 in the switched capacitor array 2009. In this
embodiment two lines 2101 are connected between power and ground
connectors, with each line 2101 comprises a first switch 2103, a
resistor 2105 (with a resistance of between about 1 Kohm and about
100 Kohm), and a second switch 2107. A third switch 2109 is
connected between the two lines 2101.
[0130] Also connected to each line is a second capacitor 2111. In
an embodiment each of the second capacitors 2111 is a
metal-oxide-metal capacitor, although any other suitable capacitor,
such as a metal-insulator-metal capacitor, may also be used. The
second capacitors 2111 may each have a capacitance between about
0.2 pF and about 4 pF, such as about 2 pF. However, any suitable
capacitance may be utilized.
[0131] The second capacitors 2111 also act as the outputs from the
switched capacitors 2100 to either other switched capacitors 2100
within the switched capacitor array 2009 or to the rest of the
digital controlled oscillator 1703. For example, while one side of
the second capacitors 2111 is connected to the lines 2101, the
other side of the second capacitors 2111 is connected to external
devices. However, any suitable connections may be utilized.
[0132] In operation, each of the first switch 2103, the second
switch 2107, and the third switch 2109 are connected to the decoder
1903. In a particular embodiment, the decoder 1903 sends a control
voltage (V.sub.con) to the first switch 2103, the second switch
2107, and the third switch 2109 in order to turn on or turn off the
individual switch capacitors 2100 within the switch capacitor array
2009. In an embodiment the control voltage V.sub.con may be less
than about 1.8 V, such as about 0.8 V. However, any suitable
voltage may be utilized.
[0133] Additionally, the switch capacitors 2100 illustrated in FIG.
21 is one of a plurality of switch capacitors 2100 within the
switch capacitor array 2009 (see FIG. 20) of each of the digital
controlled oscillators 1703. In an embodiment the switch capacitor
array 2009 may comprise between 1 and 1000 switch capacitors 2100,
such as about 100 switch capacitors 2100 within the switch
capacitor array 2009. However, any suitable number of switch
capacitors 2100 may be utilized. The decoder 1903 can turn
individual ones of the switch capacitors 2100 within the switch
capacitor array 2009 in order to tune the natural frequency and
improve the frequency resolution of the individual digital
controlled oscillators 1703.
[0134] FIG. 22 illustrates a model of the overall transformer
including the digital controlled oscillators 1703 that may be
utilized to illustrate the improvement in frequency resolution
using embodiments. For example, a model of the digital controlled
oscillator 1703 illustrated in FIG. 21 describes the equivalent
inductance L.sub.eq approximated as illustrated in Equation 1:
L eq = L + n 2 L C Sc C Equation 1 ##EQU00003##
Where L is the total inductance, C is the total capacitance, n is
the number of switched capacitors 2100 in the switched capacitor
array 2009 and C.sub.sc is the capacitance of the switch capacitor
array 2009. With this model, the oscillation frequency of the
digital controlled oscillator 1703 will be given by Equation 2:
.omega. eq = 1 L eq C = 1 LC ( 1 + n 2 C SC C ) Equation 2
##EQU00004##
[0135] As can be seen, the C.sub.SC is shrunk by n.sup.2 times. For
example, in an embodiment in which n=1/4, the capacitor shrinking
factor will be 16 and the frequency resolution is improved 16
times. The n in this equation may be between about 1/10 and about
1, such as about 1/4.
[0136] By turning on or turning off individual ones of the switch
capacitors 2100 within the switch capacitor array 2009, the decoder
can modify and tune the natural frequency of individual ones of the
digital controlled oscillators 1703 until the phase error
.PHI..sub.error detected by the skew detector 1905 (see FIG. 19)
between the first high frequency signal CKV and the second high
frequency signal CKR is either eliminated or minimized. In
particular, the equivalent capacitance of the switched capacitor
array 2009 is modified as V.sub.con turns individual ones of the
switch capacitors 2100 within the switched capacitor array 2009 on
and off. This modification of the equivalent capacitance of the
switched capacitor array 2009 can be used to control the frequency
resolution of the overall digital controlled oscillator, with the
resolution of the switch capacitor array 2009 being limited by the
minimum value of the second capacitor 2111.
[0137] By modifying the equivalent capacitance of the switched
capacitor array 2009, the natural frequency of the digital
controlled oscillator 1703 may be modified. In particular, the
decoder 1903 may control the digital controlled oscillator 1703 in
order to modify the natural frequency in order to reduce or
eliminate the phase error .PHI..sub.error between coupled ones of
the digital controlled oscillators (see FIG. 19).
[0138] FIG. 23 illustrates another embodiment of a structure which
may be used as the digital controlled oscillator 1703. In this
embodiment the active feedback device 130A is connected to power,
and the active feedback device may comprise a PMOS devices (instead
of NMOS devices as described above with respect to FIG. 20).
Additionally, the second set of inductors 2005 (with an inductance
of nL/2) are connected to the active feedback device 130A, with the
first set of inductors 2003 (with an inductance of (1-n)L/2)
connecting the second set of inductors 2005 to ground.
Additionally, the first capacitor 2007 is connected between the
second set of inductors 2005 and the active feedback device 130A,
while the switched capacitor array 2009 is connected between the
first set of inductors 2003 and the second set of inductors
2005.
[0139] FIG. 24 illustrates yet another embodiment of a structure
which may be used as the digital controlled oscillator 1703, but
which uses both PMOS transistors and NMOS transistors. In this
embodiment, a first active feedback device 2401 (comprising PMOS
devices) is connected to power while a second active feedback
device 2403 (comprising NMOS devices) is connected to ground. In an
embodiment the first active feedback device 2401 and the second
active feedback device 2403 may be similar to the active feedback
device 130A described above with respect to FIG. 1, but with their
respective devices as described herein.
[0140] Additionally in this embodiment, the first set of inductors
2003 (with an inductance of (1-n)L/2) is connected between the
first active feedback device 2401 and the second active feedback
device 2403. The second set of inductors 2005 is connected to the
first set of inductors 2003, with individual ones of the second set
of inductors 2005 being in series with individual ones of the first
set of inductors 2003. Finally, the first capacitor 2007 is
connected between the first set of inductors 2003 and the second
active feedback device 2403 while the switch capacitor array 2009
is connected between the first set of inductors 2003 and the second
set of inductors 2005. However, any suitable arrangement of
structures may be utilized.
[0141] By having multiple configurations which may be used for
different types of processes (CMOS, NMOS, PMOS), there is greater
design flexibility. For example, the specific design of the digital
controlled oscillator 1703 may be chosen for an easy incorporation
into the overall design processes. Such flexibility makes the
overall design easier to generate.
[0142] As described herein, in some embodiments a pulse injection
signal may be injected into an oscillator. The pulse injection
signal may cause the oscillator to "lock" to the frequency of the
pulse injection signal and generate an oscillating signal having a
predetermined frequency that is an integer multiple of the
frequency of the pulse injection signal. In some devices, the
predetermined frequency of the oscillator and the frequency of the
pulse injection must be within a certain "locking range" for the
frequency lock to occur.
[0143] The pulse injection signal may be configured to be injected
to an oscillator using a "common mode" or a "differential mode." In
a "common mode," for example as depicted in FIG. 1, a capacitive
device (such as capacitive device 120A) may be connected in
parallel to a switch device (such as switch device 140A) that is
used to inject the pulse injection signal into the oscillator, and
the switch device may connect or disconnect two complementary
output nodes (such as nodes 152A and 154A) of the oscillator in
accordance with a current value of the pulse injection signal. In a
"differential mode," a positive signal injector may be used to
inject a positive reference signal to a first output node of the
oscillator device, and a negative pulse injector may be used to
inject a negative reference signal to a second output node of the
oscillator device, where the negative reference signal is the
opposite of the positive reference signal. Compared to the common
mode, the differential mode may improve the locking range between
the frequency of the oscillating signals produced by the oscillator
device and the frequency of the injected pulse signals. In some
devices, compared to the common mode, the differential mode may
improve the locking range by six times or more. The frequency lock
between the oscillator device and the pulse injection signal may be
improved. For example, if the oscillator experiences frequency
drift due to process variations, temperature variations, or supply
variations, the probability that the frequency drift will cause the
oscillator device to drift out of the locking range, and thereby
unlock from the frequency of the pulse injection signal, may be
minimized.
[0144] FIG. 25 is an embodiment of an oscillator circuit 2500 with
differential pulse injection. The circuit 2500 may have a first
inductor 2502, a second inductor 2504, a capacitor C1, an active
feedback device 130A, a positive pulse injector 2506, and a
negative pulse injector 2508.
[0145] First inductor 2502 may have a first terminal connected to a
supply voltage and a second terminal connected to an output node
2510. Second inductor 2504 may have a first terminal connected to a
supply voltage and a second terminal connected to complementary
output node 2512. Capacitor C1 may have a first terminal connected
to output node 2510 and a second terminal connected to
complementary output node 2512. Active feedback device 130A may
have a first terminal connected to output node 2510, a second
terminal connected to complementary output node 2512, and a third
terminal connected to a ground node. In some embodiments, active
feedback device 130A is the same as or similar to the active
feedback device described earlier in connection with FIG. 1.
[0146] A positive pulse injector 2506 may also be connected to node
2510. In some embodiments, positive pulse injector 2506 may
comprise a transistor 2514. Transistor 2514 is a NMOS transistor in
some embodiments. A source terminal of transistor 2514 may be
connected to a ground node. A gate terminal of transistor 2514 may
be connected to a positive reference signal REF+. A drain terminal
of transistor 2514 may be connected to output node 2510.
[0147] A negative pulse injector 2508 may be connected to output
node 2512. In some embodiments, a negative pulse injector 2508 may
comprises a transistor 2516. Transistor 2516 is a PMOS transistor
in some embodiments. A source terminal of transistor 2516 may be
connected to a supply voltage. A drain terminal of transistor 2516
may be connected to node 2512. A gate terminal of transistor 2516
may be connected to a negative reference signal REF-. The negative
reference signal REF- is the inverse of the positive reference
signal REF+ in some embodiments. For example, when REF+ is high,
REF- is low, and when REF+ is low, REF- is high.
[0148] In operation, a frequency of oscillating signals produced by
oscillator circuit 2500 at output node 2510 and complementary
output node 2512 may lock to an integer multiple of the frequency
of the positive injection pulse REF+ and the negative pulse REF-.
In some embodiments, oscillator circuit 2500 with the positive
injection pulse REF+ and the negative pulse REF- may reject certain
harmonics, such as even-order harmonics, thereby improving the
locking range. Compared to the common mode, the locking range
between the frequency of the oscillating signals produced by
oscillator circuit 2500 and the frequency of the reference pulse
signals REF+ and REF- may increase by six times or more. For
example, in some embodiments the locking range may increase by 6.7
times compared to the common mode.
[0149] FIG. 26 is an embodiment of an oscillator circuit 2600 with
differential pulse injection. The circuit 2600 may have a first
inductor 2602, a second inductor 2604, a capacitor C1, an active
feedback device 130A, a positive pulse injector 2606, and a
negative pulse injector 2608. Compared to the oscillator circuit
2500 depicted in FIG. 25, the positions of the first inductor and
the second inductor, and the position of the active feedback device
130A, have been switched.
[0150] Active feedback device 130A may have a first terminal
connected to a supply voltage, a second terminal connected to node
2610, and a third terminal connected to node 2612. In some
embodiments, active feedback device 130A is the same as or similar
to the active feedback device described earlier in connection with
FIG. 1. Capacitor C1 may have a first terminal connected to node
2610 and a second terminal connected to node 2612. A first inductor
2602 may have a first terminal connected to node 2610 and a second
terminal that is grounded. A second inductor 2604 may have a first
terminal connected to node 2612 and a second terminal that is
grounded.
[0151] A positive pulse injector 2606 may also be connected to node
2610. In some embodiments, positive pulse injector 2606 may
comprise a transistor 2614. Transistor 2614 is a NMOS transistor in
some embodiments. A source terminal of transistor 2614 may be
connected to a ground node. A gate terminal of transistor 2614 may
be connected to a positive reference signal REF+. A drain terminal
of transistor 2614 may be connected to node 2610.
[0152] A negative pulse injector 2608 may be connected to node
2612. In some embodiments, a negative pulse injector 2608 may
comprises a transistor 2616. Transistor 2616 is a PMOS transistor
in some embodiments. A source terminal of transistor 2616 may be
connected to a supply voltage. A drain terminal of transistor 2616
may be connected to node 2612. A gate terminal of transistor 2616
may be connected to a negative reference signal REF-. The negative
reference signal REF- is the inverse of the positive reference
signal REF+ in some embodiments. For example, when REF+ is high,
REF- is low, and when REF+ is low, REF- is high.
[0153] In operation, a frequency of oscillating signals produced by
oscillator circuit 2600 may lock to an integer multiple of the
frequency of the positive injection pulse REF+ and the negative
pulse REF-. In some embodiments, oscillator circuit 2600 with the
positive injection pulse REF+ and the negative pulse REF- may
reject certain harmonics, such as even-order harmonics, thereby
improving the locking range.
[0154] Compared to the common mode, the locking range between the
oscillating signals produced by oscillator circuit 2600 and the
frequency of the reference pulse signals REF+ and REF- may increase
by six times or more. For example, in some embodiments the locking
range may increase by 6.7 times compared to the common mode.
[0155] FIG. 27 is an example of an oscillator circuit 2700 with
differential pulse injection. The circuit 2700 may have a first
inductor 2704, a capacitor C1, a first active feedback device
130AA, a second active feedback device 130AB, a positive pulse
injector 2706, and a negative pulse injector 2708. Compared to the
oscillator circuit 2500 depicted in FIG. 25 and the oscillator
circuit 2600 depicted in FIG. 26, oscillator circuit 2700 includes
only a first inductor 2704 but includes both a first active
feedback device 130AA and a second active feedback device
130AB.
[0156] Active feedback device 130AA may have a first terminal
connected to a supply voltage, a second terminal connected to node
2710, and a third terminal connected to node 2712. Capacitor C1 may
have a first terminal connected to node 2710 and a second terminal
connected to node 2712. First inductor 2704 may be connected in
parallel to capacitor C1. A first terminal of first inductor 2704
may be connected to node 2710 and a second terminal of first
inductor 2704 may be connected to node 2712. Second active feedback
device 130AB may have a first terminal that is connected to node
2710, a second terminal that is connected to node 2712, and a third
node that is grounded.
[0157] A positive pulse injector 2706 may also be connected to node
2710. In some embodiments, positive pulse injector 2706 may
comprise a transistor 2714. Transistor 2714 is a NMOS transistor in
some embodiments. A source terminal of transistor 2714 may be
connected to a ground node. A gate terminal of transistor 2714 may
be connected to a positive reference signal REF+. A drain terminal
of transistor 2714 may be connected to node 2710.
[0158] A negative pulse injector 2708 may be connected to node
2712. In some embodiments, negative pulse injector 2708 may
comprise a transistor 2716. Transistor 2716 is a PMOS transistor in
some embodiments. A source terminal of transistor 2716 may be
connected to a supply voltage. A drain terminal of transistor 2716
may be connected to node 2712. A gate terminal of transistor 2716
may be connected to a negative reference signal REF-. The negative
reference signal REF- is the inverse of the positive reference
signal REF+ in some embodiments. For example, when REF+ is high,
REF- is low, and when REF+ is low, REF- is high.
[0159] In operation, a predetermined frequency of oscillating
signals produced by oscillator circuit 2700 may lock to an integer
multiple of the frequency of the positive injection pulse REF+ and
the negative pulse REF-. In some embodiments, oscillator circuit
2700 with the positive injection pulse REF+ and the negative pulse
REF- may reject certain harmonics, such as even-order harmonics,
thereby improving the locking range. Compared to the common mode,
the locking range between the oscillating signals generated by
oscillator circuit 2700 and the frequency of the reference pulse
signals REF+ and REF- may increase by six times or more. For
example, in some embodiments the locking range may increase by 6.7
times compared to the common mode.
[0160] FIG. 28 depicts a graph showing pulse width of the injected
signal versus the frequency of the signals produced by an
oscillator for both the common mode and the differential mode in
accordance with some embodiments. As shown in FIG. 28, as compared
to the common mode, the differential mode has a locking range that
is much larger. For example, when the oscillator produces
oscillating signals having a frequency of 4 GHz, the locking range
of the differential mode may be 6.7 times the size of the common
mode.
[0161] As described herein, in some embodiments a pulse injection
signal may be injected to an oscillator to cause the oscillator to
create an oscillating signal having a predetermined frequency that
is an integer multiple of the frequency of the pulse injected
signal. In a "common mode," a capacitive device may be connected in
parallel to a switch device that is used to inject the pulse
injection signal into the oscillator. In a "differential mode," a
positive signal injector may be used to inject to a positive
reference signal to a first output node of the oscillator device,
and a negative pulse injector may be used to inject a negative
reference signal to a second output node of the oscillator device,
where the negative reference signal is the opposite of the positive
reference signal. Compared to the common mode, the differential
mode may improve the locking range between the frequency of the
oscillating signals produced by the oscillator and the frequency of
the injected pulse signal. In some devices, compared to the common
mode, the differential mode may improve the locking range by 6
times or more. The frequency lock between the oscillator device and
the pulse injection signal may be improved. For example, if the
oscillator device experiences frequency drift due to process
variations, temperature variations, or supply variations, the
probability that the frequency drift will cause the oscillator
device to drift out of the locking range, and thereby unlock from
the frequency of the pulse injection signal, may be minimized.
[0162] As described above, in some embodiments a pulse injection
signal may be injected to an oscillator. In some devices, a delay
cell circuit may be used to generate a pulse injection signal. For
example, a pulse injection signal may be generated by comparing a
first signal to a second signal, where one of the first and the
second signals is delayed with respect to the other signal.
However, common delay cell circuits may create undesirable noise in
the pulse injection signal. For example, common delay cell circuits
may degrade the slew rate of the rising and falling edge of the
pulse signal and create undesirable noise.
[0163] FIG. 29 depicts an embodiment of a circuit 2900 that may
generate a pulse signal using a first signal having a programmable
delay. By using a first signal with a programmable delay, the
circuit 2900 avoids the use of common delay cell circuits to
generate a pulse signal. As such, the pulse signal produced by the
circuit 2900 may have less noise.
[0164] As shown in FIG. 29, a crystal oscillator 2902 generates a
sinusoidal signal. An output of the crystal oscillator 2902 is
connected to an input of a first coupling capacitor 2904 and a
second coupling capacitor 2906.
[0165] An output of the first coupling capacitor 2904 is connected
to inverter 2916. In some embodiments, inverter 2916 may include a
transistor 2924 and a transistor 2926. In some embodiments,
transistor 2924 is a PMOS transistor and transistor 2926 is an NMOS
transistor. The output of first coupling capacitor 2904 may be
connected to input node 2938. A gate terminal of transistor 2924
and a gate terminal of transistor 2926 may also be connected to
input node 2938. A source terminal of the transistor 2924 may be
connected to a supply voltage and a drain terminal of the
transistor 2924 may be connected to output node 2936. A drain
terminal of the transistor 2926 may also be connected to output
node 2936. A source transistor of the transistor 2926 may be
grounded. A resistor 2928 may be connected between input node 2938
and output node 2936.
[0166] The inverter 2916 may be connected to pull down block 2918.
Pull down block 2918 includes one or more pull down branches
M.sub.ni, each of which comprises a first transistor and a second
transistor. The first transistor and the second transistor are NMOS
transistors in some embodiments. Two pull down branches M.sub.ni
are depicted in FIG. 29. In some embodiments, up to five pull down
branches M.sub.ni may be used. For example, i may be an integer
from 0 to 4 inclusive. In each pull down branch, the first
transistor may have a drain terminal connected to output node 2936
of the inverter 2916, a gate terminal connected to the input node
2938 of the inverter 2916, and a source terminal connected to a
drain terminal of the second NMOS transistor. The second transistor
may have a gate terminal connected to a programmable input signal
D[i], where i may be an integer from 0 to 4. A source terminal of
the second transistor may be grounded.
[0167] Pull down block 2918 and inverter 2916 may each be connected
to inverter 2922. For example, an input node 2940 of inverter 2922
may be connected to output node 2936 of inverter 2916 and to a
respective drain terminal of each first transistor of each pull
down branch M.sub.ni. Inverter 2922 may include a PMOS transistor
2942 and an NMOS transistor 2944. A source terminal of PMOS
transistor 2942 is connected to a supply voltage, a gate terminal
of transistor 2942 is connected to input node 2940, and a drain
terminal of transistor 2942 is connected to inverter output node
2946. A drain terminal of transistor 2944 is connected to inverter
output node 2946, a gate terminal of transistor 2944 is connected
to input node 2940, and a source terminal of transistor 2944 is
grounded.
[0168] A comparator 2946 has an input terminal that is connected to
output node 2946. In some embodiments, comparator 2946 comprises an
AND gate.
[0169] As discussed above, the output of crystal oscillator 2902
may be connected to a first terminal of second coupling capacitor
2906. A second terminal of second coupling capacitor 2906 may be
connected to input node 2948 of inverter 2910. Inverter 2910 may
include a transistor 2930, a resistor 2932, and a transistor 2934.
In some embodiments, transistor 2930 is a PMOS transistor and
transistor 2934 is an NMOS transistor. A source terminal of
transistor 2930 may be connected to a supply voltage. A gate
terminal of transistor 2930 may be connected to input node 2948. A
drain terminal of transistor 2930 may be connected to output node
2950. Resistor 2932 may have a first terminal connected to input
node 2948 and a second terminal connected to output node 2950.
Transistor 2934 may have a drain terminal connected to output node
2950, a gate terminal connected to input node 2948, and a source
terminal that is grounded.
[0170] Inverter 2910 may be connected to inverter 2912. For
example, output node 2950 of inverter 2910 may be connected to
input node 2952 of inverter 2912. Inverter 2912 may include a
transistor 2954 and a transistor 2956. In some embodiments,
transistor 2954 is a PMOS transistor and transistor 2956 is an NMOS
transistor. A source terminal of transistor 2954 may be connected
to a supply voltage, a gate terminal of transistor 2954 may be
connected to input node 2952, and a drain terminal of transistor
2954 may be connected to output node 2958. A drain terminal of
transistor 2956 may be connected to output node 2958, a gate
terminal of transistor 2956 may be connected to input node 2952,
and a source terminal of transistor 2956 may be grounded.
[0171] Inverter 2912 may be connected to inverter 2914. For
example, output node 2958 of inverter 2912 may be connected to
input node 2960 of inverter 2914. Inverter 2914 may include a
transistor 2962 and a transistor 2964. In some embodiments,
transistor 2962 is a PMOS transistor and transistor 2964 is an NMOS
transistor. A source terminal of transistor 2962 may be connected
to a supply voltage, a gate terminal of transistor 2962 may be
connected to input node 2960, and a drain terminal of transistor
2962 may be connected to output node 2966. A drain terminal of
transistor 2964 may be connected to output node 2966, a gate
terminal of transistor 2964 may be connected to input node 2960,
and a source terminal of transistor 2964 may be grounded.
[0172] Output node 2966 of inverter 2914 may be connected to a
second terminal of comparator 2946. An output of the comparator
2946 may be connected to an oscillator. For example, the output of
the comparator 2946 may be connected to switch devices 140A and/or
140B of FIG. 1 using buses 170A and/or 170B. As another example,
the output of comparator 2946 may be connected to driver 520 of
FIG. 5.
[0173] Circuit 2900 may generate a pulse signal INJ. While the
pulse signal is designated as INJ in connection with FIGS. 29-31,
the pulse injection signal is labeled with other designations in
other Figures, such as REF+ or REF- in FIGS. 25-27. Further, for
avoidance of doubt it is noted that the REF clock signal in FIGS.
25-27 may be a different signal than the REF, REF+, and/or REF-
signals discussed in connection with previous Figures.
[0174] During operation, crystal oscillator 2902 may generate a
sinusoidal signal. In the top half of the circuit, first coupling
capacitor 2904, inverter 2916, pull down block 2918, and inverter
2922 generate a delay clock signal. In the bottom half of the
circuit, second coupling capacitor 2906, inverter 2910, inverter
2912, and inverter 2914 generate a REF clock signal. Comparator
2946 compares the delay clock signal to the REF clock signal, and
generates pulse signal INJ according to the results of the
comparison. A timing diagram of the sinusoidal signal generated by
crystal oscillator 2902, the delay clock signal, the REF clock
signal, and the pulse signal INJ, is shown in FIG. 31.
[0175] As discussed above, the delay clock signal is generated by
first coupling capacitor 2904, inverter 2916, pull down block 2918,
and inverter 2922. A sinusoidal signal output from crystal
oscillator 2902 is input into input node 2938 of inverter 2916.
Inverter 2916 converts the sinusoidal signal into a square wave
signal having an opposite polarity from the input sinusoidal
signal, where the square wave signal has a high value or a low
value. Whether the square wave signal has a high value or a low
value depends on the value of the sinusoidal signal at a current
instance and on a threshold voltage of the inverter. For example,
when the voltage of the sinusoidal signal is below the threshold
voltage of the inverter, the square wave signal that is output from
inverter 2916 is a high value. When the sinusoidal signal has a
voltage level that is above the threshold voltage of the inverter,
the square wave signal that is output from inverter 2916 is a low
value.
[0176] Inverter 2922 inverts the value of the input square wave
that is received from inverter 2916 and outputs a square wave (the
delay clock signal) that is the substantial inverse of the input
square wave. For example, when the signal at input node 2940 has a
low value, the delay clock signal has a high value. When the signal
an input node 2940 has a high value, the delay clock signal has a
low value.
[0177] As discussed above, in some embodiments it may be desirable
to generate a first signal having a programmable delay, which may
in turn be used to generate a pulse signal having a desired pulse
width. In some embodiments, one or more of control signals
D[0]-D[i] may be used to produce a square wave having a
programmable edge delay, which may control a pulse width of the INJ
signal produced by circuit 2900.
[0178] In each pull down branch, the first transistor M.sub.ni is
activated when the value of the sinusoidal signal that is passed
through the first coupling capacitor 2904 has a sufficient voltage
to turn on the first transistor M.sub.ni. The second transistor of
each pull down branch may be activated when the respective control
signal D[0]-D[i] is activated, As such, each respective pull down
branch is activated when the value of the sinusoidal signal that is
passed through the first coupling capacitor 2904 has a sufficient
voltage to turn on the first transistor M.sub.ni and when the
respective control signal D[0]-D[i] is activated.
[0179] When one or more of the pull down branches is activated, the
effect of the activation is to effectively increase the strength of
transistor 2926, and adjust the voltage threshold of inverter 2916
so that a higher voltage is required for the inverter 2916 to
output a square wave having a low value instead of a high value.
The higher the number of pull down branches that are active, the
higher the voltage threshold of inverter 2916 is adjusted.
[0180] The increase in the threshold voltage of inverter 2916
results in a shorter period of time in which the sinusoidal signal
that is passed through first coupling capacitor 2904 has a voltage
that is high enough to cause the inverter 2916 to output a low
signal. In effect, the time instance in which the output of
inverter 2916 changes from a high output value to a low output
value is delayed with respect to when the output signal from
inverter 2916 would have changed without the pull down branches
being active, because it takes longer for the input sinusoidal
signal to reach the higher threshold voltage. Further, the time
instance in which the output of inverter 2916 changes from a low
output value to a high output value is earlier with respect to when
the change would have occurred without one or more pull down
branches being active. The magnitude of the time changes depends on
how many of the one or more pull down branches are active, with a
greater number of pull down branches causing a greater change of
time. The modified pulse width of the square wave is input to
inverter 2922. Inverter 2922 inverts the modified pulse width
signal and outputs the delay clock signal.
[0181] Referring to FIG. 31, a timing diagram is depicted
indicating the modification of the pulse width of the delay clock
signal. Compared to the input sinusoidal wave, when one or more
pull down branches is turned on, the delay clock signal changes
from a low value to a high value at a time that corresponds to the
input sinusoidal signal having a higher voltage than would
otherwise have occurred, and the delay clock signal changes from
high to low at a time that corresponds to the input sinusoidal
signal having a higher voltage than would otherwise have prompted
the change in the signal value.
[0182] FIG. 31 also shows that, compared to the REF clock signal,
the delay clock signal is substantially the inverse of the REF
clock signal, but that edges of the delay clock signal are offset
from the edges of the REF clock signal. The time offset between the
edges of the REF clock signal and the edges of the delay clock
signal correspond to the change in the voltage threshold of
inverter 2916 that are caused by pull down branches M.sub.ni. As
such, when comparator 2946 compares the REF clock signal and the
delay clock signal, pulse injection signal INJ is generated, as
shown in FIG. 31. The pulse width of the signal pulses of pulse
injection signal INJ may correspond to the time delay that is
caused by the change in the voltage threshold of inverter 2916 that
is caused by activated pull down branches M.sub.ni.
[0183] Circuit 2900 of FIG. 29 may generate a pulse signal that has
two pulses per cycle of the sinusoidal signal generated by crystal
oscillator 2902. For example, as shown in FIG. 31, circuit 2900 of
FIG. 29 may generate a pulse signal INJ that has a high value pulse
in each half cycle of the sinusoidal signal generated by crystal
oscillator 2902. In some embodiments it may be preferred to
generate a pulse signal that has only one pulse per cycle.
[0184] FIG. 30 depicts a circuit 3000 in which a comparator 2968 is
used to modify circuit 2900 to generate a pulse signal that has
only one pulse per cycle of the sinusoidal signal generated by
crystal oscillator 2902. As shown in FIG. 30, the output of circuit
2900, pulse signal INJ, is connected to an input of comparator
2968. In some embodiments, comparator 2968 comprises an AND gate.
The REF clock signal generated by inverter 2914 of circuit 2900 is
connected to an input of buffer 2972. An output of buffer 2972 is
connected to an input of buffer 2970. A capacitor 2974 is connected
between the output of buffer 2972 and a ground node. An output of
buffer 2970 is connected to an input of comparator 2968. The output
buffer 2970 generates the window signal depicted in the timing
diagram of FIG. 31.
[0185] As shown in FIG. 31, for every cycle of the sinusoidal
signal, the window signal has a high value for a first pulse of the
INJ signal and has a low value for a second pulse of the INJ
signal. As such, when the window signal is compared to the INJ
signal by comparator 2968, the first pulse of the INJ signal is
passed through comparator 2968 and the second pulse is
eliminated.
[0186] A method of operating circuit 2900 of FIG. 29 and/or circuit
3000 of FIG. 30 is depicted in FIG. 32. In step 3102, a sinusoidal
signal is generated. For example, crystal oscillator 2902 of FIG.
29 may generate a sinusoidal signal. In step 3104, a voltage
threshold of a first inverter is adjusted. For example, a voltage
threshold of inverter 2916 of FIG. 29 may be adjusted by activating
one or more pull down branches M.sub.ni using control signals
D[0]-D[i]. In step 3106, a first signal is generated using the
sinusoidal signal. For example, inverter 2916 may generate a first
signal using the sinusoidal signal. In step 3108, a second signal
is generated by inverting the first signal. For example, inverter
2922 of FIG. 29 may generate a second signal by inverting the
second signal. In step 3110 a first reference signal is generated.
For example, in FIG. 29 crystal oscillator 2902, second coupling
capacitor 2906, and/or inverters 2910, 2912, and 2914 may generate
a first reference signal. In step 3112 the second signal is
compared to the first reference signal to generate a first pulse
signal. For example, in FIG. 29 comparator 2946 may compare the
second signal to the first reference signal to generate a first
pulse signal. In step 3114 a second reference signal is generated.
For example, in FIG. 30 a second reference signal is generated by
buffers 2972 and 2970 and capacitor 2974. In step 3116 the first
pulse signal is compared to the second reference signal to generate
a second pulse signal. For example, in FIG. 30 comparator 2968
compares the first pulse signal to the second reference signal to
generate a second pulse signal.
[0187] As described above, circuit 2900 generates a pulse injection
signal INJ using a first signal having a programmable edge delay.
Because of the first signal, circuit 2900 generates a pulse
injection signal having a programmable pulse width that does not
use any delay cell circuits. As such, noise may be reduced or
eliminated.
[0188] In accordance with one embodiment, a circuit includes a
coupling structure and a first inductive device. The coupling
structure includes two or more conductive loops and a set of
conductive paths electrically connecting the two or more conductive
loops. The first inductive device is magnetically coupled with a
first conductive loop of the two or more conductive loops.
[0189] In accordance with another embodiment, a circuit includes a
first oscillator comprising an inductive device, a second
oscillator comprising an inductive device, and a coupling
structure. The coupling structure includes a first conductive loop
magnetically coupled with the inductive device of the first
oscillator, a second conductive loop magnetically coupled with the
inductive device of the second oscillator, and a set of conductive
paths electrically connecting the first conductive loop and the
second conductive loop.
[0190] In accordance with another embodiment, a method includes
generating an induced current at a first conductive loop of a
coupling structure responsive to a first magnetic field generated
by a first inductive device of a first oscillator. The induced
current is transmitted to a second conductive loop of the coupling
structure through a set of conductive paths of the coupling
structure electrically connecting the first and second conductive
loops. A second inductive device of a second oscillator is
magnetically coupled with the first inductive device of the first
oscillator through the coupling structure.
[0191] In accordance with yet another embodiment, a integrated
circuit device comprising a first digital controlled oscillator and
a second digital controlled oscillator coupled to the first digital
controlled oscillator is provided. A skew detector is connected to
outputs of both the first digital controlled oscillator and the
second digital controlled oscillator, and a decoder connected to an
output of the skew detector, wherein an output from the decoder is
connected to a switch capacitor array within the first digital
controlled oscillator.
[0192] In accordance with another embodiment, a integrated circuit
device comprising a first digital controlled oscillator is
provided. The first digital controlled oscillator comprises a first
set of inductors, each one of the first set of inductors having a
first inductance, and a second set of inductors, each one of the
second set of inductors having a second inductance different from
the first inductance, wherein individual ones of the first set of
inductors are in series with individual ones of the second set of
inductors. A switched capacitor array is connected between the
first set of inductors and the second set of inductors, and an
active feedback device is connected to one of the first set of
inductors or the second set of inductors. A second digital
controlled oscillator is coupled to the first digital controlled
oscillator.
[0193] In accordance with yet another embodiment, a method
comprising determining a first skew between a first clock signal
and a second clock signal, the first clock signal originating from
a first digital controlled oscillator, the second clock signal
originating from a second digital controlled oscillator coupled to
the first digital controlled oscillator is provided. A natural
frequency of the first digital controlled oscillator is modified by
sending a signal to a switched capacitor array within the first
digital controlled oscillator, the signal being based on the first
skew.
[0194] In accordance with another embodiment, an integrated circuit
is provided. The integrated circuit includes an LC tank oscillator
circuit. The integrated circuit also includes a positive pulse
injector connected to a first output node of the LC tank oscillator
circuit, the positive pulse injector configured to inject a
positive reference signal into the LC tank oscillator circuit. The
integrated circuit also includes a negative pulse injector
connected to a second output node of the LC tank oscillator
circuit, the negative pulse injector configured to inject a
negative reference signal into the LC tank oscillator circuit. The
negative reference signal is an inverse of the positive reference
signal. In an embodiment the LC tank oscillator circuit comprises:
a first inductor; a second inductor; a capacitor; and an active
feedback device. In an embodiment the first inductor is connected
to the first output node, the second inductor is connected to the
second output node, and the capacitor is connected between the
first output node and the second output node. In an embodiment the
active feedback device is connected to a supply voltage. In an
embodiment the active feedback device is connected to a ground
node. In an embodiment the positive pulse injector comprises a
Negative Metal Oxide Semiconductor (NMOS) transistor and the
negative pulse injector comprises a Positive Metal Oxide
Semiconductor (PMOS) transistor. In an embodiment he NMOS
transistor comprises a drain terminal connected to the first output
node, a gate terminal connected to the positive reference signal,
and a source terminal connected to a ground node; and the PMOS
transistor comprises a source terminal connected to a supply
voltage, a gate terminal connected to the negative reference
signal, and a drain terminal connected to the second output node.
In an embodiment he LC tank oscillator circuit comprises: an
inductor and a capacitor connected in parallel; a first active
feedback device connected to a supply voltage; and a second active
feedback device connected to a ground node.
[0195] In accordance with another embodiment, an integrated circuit
is provided. The integrated circuit includes a signal generator and
a first inverter connected to the signal generator through a first
coupling capacitor. A reference signal generating circuit is
connected to the signal generator through a second coupling
capacitor, the reference signal generating signal being configured
to generate a reference signal. The integrated circuit also
includes a pull down block, comprising one or more pull down
branches, where each pull down branch of the one or more pull down
branches is connected to an output of the first inverter and to one
or more programmable input signals, and where each pull down branch
is configured to adjust a voltage threshold of the first inverter
in response to the one or more programmable input signals to which
the respective pull down branch is connected being activated. The
integrated circuit also includes a second inverter, where an input
of the second inverter is connected to the output of the first
inverter. The integrated circuit also includes a first comparator
configured to compare an output of the second inverter to the
reference signal to generate a pulse signal. In an embodiment, the
signal generator is configured to generate a sinusoidal signal, and
wherein the first inverter outputs a square wave signal. In an
embodiment the reference signal generating circuit comprises a
plurality of inverters. In an embodiment the width of the pulses of
the pulse signal correspond to the voltage threshold of the first
inverter. In an embodiment the circuit further includes a second
comparator, wherein the pulse nal is connected to an input of the
second comparator. In an embodiment ch pull down branch of the one
or more pull down branches comprises: a first transistor; and a
second transistor; where the first transistor has a control
terminal connected to an input of the first inverter; and where the
second transistor has a control terminal connected to one of the
one or more programmable input signals. In an embodiment the first
comparator is an AND gate. In an embodiment the first inverter
comprises a resistor connected between an input of the inverter and
the output of the inverter.
[0196] In accordance with another embodiment a method is provided.
The method includes generating, by a signal generator, a sinusoidal
signal. The method also includes adjusting, by one or more
programmable pull down branches, a voltage threshold of a first
inverter. The method also includes generating, by the first
inverter, a first signal using the sinusoidal signal, where the
first signal is a square wave signal alternating between a low
value and a high value, and where a time duration of the low values
of the first signal depend at least in part on the adjusted voltage
threshold of the first inverter. The method also includes
generating a second signal by inverting the first signal. The
method also includes generating a first reference signal. The
method also includes generating a first pulse signal by comparing
the second signal and the first reference signal. In an embodiment
adjusting the voltage threshold of the first inverter comprises:
activating, by one or more control signals, a set of the one or
more programmable pull down branches, the set comprising a quantity
of the one or more programmable pull down branches, the quantity
being in a range of 1 to 5; wherein a magnitude of the adjustment
of the voltage threshold of the first inverter is determined
according the quantity of the one or more programmable pull down
branches. In an embodiment generating the first reference signal
comprises: inverting the sinusoidal signal to generate a third
signal; inverting the third signal to obtain a fourth signal; and
inverting the fourth signal to obtain the first reference signal.
In an embodiment the method also includes generating a second
reference signal using the first reference signal; and comparing
the first pulse signal to the second reference signal to generate a
second pulse signal.
[0197] The foregoing outlines features of several embodiments so
that those skilled in the art may better understand the aspects of
the present disclosure. Those skilled in the art should appreciate
that they may readily use the present disclosure as a basis for
designing or modifying other processes and structures for carrying
out the same purposes and/or achieving the same advantages of the
embodiments introduced herein. Those skilled in the art should also
realize that such equivalent constructions do not depart from the
spirit and scope of the present disclosure, and that they may make
various changes, substitutions, and alterations herein without
departing from the spirit and scope of the present disclosure.
* * * * *