Quadrature-based injection locking of ring oscillators
View Patent ↗Technologies are generally described for quadrature-based injection-locking of ring oscillators. In some examples, an external signal may be injected into a ring oscillator. Phase signals may be measured from within the ring oscillator and used to determine a mean quadrature error (MQE) that characterizes the difference in frequency between the external signal and the ring oscillator's natural frequency. A control signal may then be generated from the MQE and used to adjust the ring oscillator natural frequency to reduce the difference between the ring oscillator natural frequency and the external signal.
1. An injection-locked ring oscillator system, comprising:
a plurality of inverters configured to receive an external signal with an injection frequency;
a phase detector module coupled to the plurality of inverters, wherein the phase detector module is configured to:
detect a first phase signal, formed from a coupling of a natural frequency of the injection-locked ring oscillator system and the injection frequency, from a first inverter of the plurality of inverters;
detect a second phase signal, formed from the coupling of the natural frequency and the injection frequency, from a second inverter of the plurality of inverters;
detect a mismatch between the injection frequency and the natural frequency; and
identify phase errors in the first phase signal and the second phase signal based on the mismatch; and
a control module coupled to the phase detector module, wherein the control module is configured to:
generate control signal based on the phase errors, wherein the control signal is configured to control the injection-locked ring oscillator system.
2. The injection-locked ring oscillator system of claim 1 , wherein the control signal is configured to adjust the natural frequency to reduce a difference between the natural frequency and the injection frequency.
3. The injection-locked ring oscillator system of claim 1 , wherein at least one of the plurality of inverters is configured to output oscillation signal, and wherein the phase detector module is further configured to:
reduce phase errors in the oscillation signal by a reduction of a frequency difference between the injection frequency and the natural frequency.
4. The injection-locked ring oscillator system of claim 1 , wherein the phase detector module is further configured to:
determine a mean quadrature error (MQE) from at least the first phase signal and the second phase signal, wherein the MQE is usable to generate the control signal to control the injection-locked ring oscillator system.
5. The injection-locked ring oscillator system of claim 4 , wherein the MQE includes an average quadrature phase error, and wherein the average quadrature phase error includes a phase difference between the first phase signal and the second phase signal.
6. The injection-locked ring oscillator system of claim 5 , wherein the MQE is determined by:
M
Q
E
=
π
2
(
ω
inj
ω
0
+
ω
b
ω
0
-
1
)
,
where
ω
inj
=
2
π
f
inj
,
ω
0
=
2
π
f
0
,
ω
b
=
(
ω
0
-
ω
inj
)
2
-
ω
l
2
,
and
ω
l
=
ω
0
2
Q
k
,
where
f inj =is a measurement of the injection frequency and is 15 gigahertz (GHz), f 0 is a measurement of the natural frequency GHz), k=0.2, and Q=1.25.
7. The injection-locked ring oscillator system of claim 6 , wherein the phase detector module is further configured to:
detect a locked state of the injection-locked ring oscillator system, wherein the locked state includes
(ω 0 −ω inj ) 2 <ω l 2 ; and
reduce the phase errors in an oscillation signal by an adjustment of a value of f 0 until a value of the MQE is substantially zero, wherein the value of the MQE is substantially zero when the value of f 0 equals a value of f inj .
8. The injection-locked ring oscillator system of claim 6 , wherein the phase detector module is further configured to:
compare a value of f 0 to a value of f inj ;
determine the value of f 0 as being less than the value of f inj ; and
in response to a determination that the value of f 0 is less than the value of f inj , identify a positive value of the MQE.
9. The injection-locked ring oscillator system of claim 8 , further comprising a low-pass filter module coupled to the phase detector module, wherein the phase detector module is further configured to:
transmit the MQE to the low-pass filter module, wherein the low-pass filter module is configured to:
increase a magnitude of the control signal; and
increase a supply voltage to at least one of the plurality of inverters based on the magnitude of the control signal, wherein the increase in the supply voltage increases the value of f 0 .
10. The injection-locked ring oscillator system of claim 6 , wherein the phase detector module is further configured to:
compare a value of f 0 to a value of f inj ;
determine the value of f 0 as being greater than the value of f inj ; and
in response to a determination that the value of f 0 is greater than the value of f inj , identify a negative value of the MQE.
11. The injection-locked ring oscillator system of claim 10 , further comprising a low-pass filter module coupled to the phase detector module, wherein the phase detector module is further configured to:
transmit the MQE to the low-pass filter module, wherein the low-pass filter module is configured to:
decrease a magnitude of the control signal; and
decrease a supply voltage to at least one of the inverters of the plurality of inverters based on the magnitude of the control signal, wherein the decrease in the supply voltage decreases the value of f 0 .
12. A clock signal distribution circuit, comprising:
a clock signal injection stage, wherein the clock signal injection stage is configured to:
receive a clock signal; and
use the clock signal to output an injection signal with an injection frequency;
a ring oscillator with a natural frequency and coupled to the clock signal injection stage, wherein the ring oscillator configured to
receive the injection signal; and
output oscillation signals; and
a quadrature phase detector module coupled to the ring oscillator, wherein the quadrature phase detector module is configured to:
detect, from the ring oscillator, phase signals formed from a coupling of the natural frequency and the injection frequency; and
determine a mean quadrature error (MQE) from the phase signals, wherein the MQE is usable to generate a control signal to control the ring oscillator.
13. The clock signal distribution circuit of claim 12 , wherein the clock signal includes an optical clock signal.
14. The clock signal distribution circuit of claim 13 , wherein the clock signal injection stage is further configured to:
convert the optical clock signal into an electrical clock signal using a photodiode.
15. The clock signal distribution circuit of claim 14 , wherein the clock signal injection stage is further configured to:
provide the electrical clock signal as a time-varying current signal to the ring oscillator.
16. The clock signal distribution circuit of claim 12 , wherein a first oscillation signal of the oscillation signals is offset by at least 90° relative to a second oscillation signal of the oscillation signals.
17. A method to injection-lock a ring oscillator that includes a plurality of inverters and a natural frequency, the method comprising:
injecting an external signal with an injection frequency into at least one of the plurality of inverters;
detecting a first phase signal, formed from a coupling of the natural frequency and the injection frequency, from a first inverter in the plurality of inverters;
detecting a second phase signal, formed from the coupling of the natural frequency and the injection frequency, from a second inverter in the plurality of inverters;
detecting a mismatch between the injection frequency and the natural frequency;
identifying, phase errors in the first phase signal and the second phase signal based on the mismatch; and
generating a control signal based on the phase errors, wherein the control signal is configured to control the ring oscillator.
18. The method of claim 17 , further comprising:
reducing the phase errors in the first phase signal and the second phase signal by a reduction of a difference between the frequency of the external signal and the natural frequency.
19. The method of claim 17 , further comprising:
determining a mean quadrature error (MQE) from at least the first phase signal and the second phase signal, wherein the MQE is usable to generate the control signal to control the ring oscillator.
20. The method of claim 19 , further comprising:
adjusting the natural frequency of the ring oscillator to reduce a magnitude of the MQE by one of:
increasing the natural frequency in response to a detection of a value of the MQE as being greater than zero; and
decreasing the natural frequency in response to the detection of the value of the MQE as being less than zero.