1. LC Voltage Control Oscillator AAC
ECE 665 (ESS)
LC Voltage Control Oscillator AAC
A Stable Loss-Control Feedback Loop to Regulate the oscillation Amplitude of LC VCO’s
Problem: Previously reported AAC loops use a conditionally stable negative feedback loop
Motivation: To propose a practically stable negative feedback loop
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2. VCO Amplitude Control More on VCO AAC loop Fast and reliable start up.
Optimal bias point in terms of phase noise performance.
Adequate amplitude over wide oscillation frequency range.
Variations of oscillation amplitude could be fast when other digital blocks pull the ground or the power supply rails.
VCO-based Q-tuning.
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3. LC Filters Active LC filters However,
ECE 665 (ESS
LC Filters
Active LC filters
The advent of highly integrated wireless communication transceivers.
Persistent effort to improve the quality of on-chip spiral inductors.
Superior dynamic range performance.
However,
Reactive elements integrated on silicon are more non-ideal than corresponding discrete parts.
Automatic tuning is a major challenge.
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4. LC Filters: Q-Tuning Tuning techniques Direct tuning: Self-tuning
Filter is the plant in the tuning system
Tuning accuracy doesn’t rely on matching.
Indirect tuning: master-slave
VCF-based : Master is a filter
VCO-based : Master is a VCO
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5. LC Filters: Q-Tuning VCF-base tuning VCO-base tuning
A reference signal with low harmonic content.
A phase detector having low offsets.
Since output amplitude varies with frequency thus Q-tuning loop heavily relies on frequency tuning loop.
VCO-base tuning
No reference signal is needed.
Amplitude and phase of the VCO are independent, theoretically, thus the Q-tuning and frequency tuning loops are not affecting each other.
Leakage of the VCO output to signal path.
Inherent nonlinearity of VCO and its effect on Q-tuning accuracy.
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6. VCO-Based Q-Tuning Principle of Operation VCO: Large signal
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7. VCO-Based Q-Tuning
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8. VCO-Based Q-Tuning Experimental results Q=50, 75, 115, 160
3- F. Bahmani, E. Sanchez-Sinencio, ”VCO-based quality factor tuning of a second-order LC filter at 2.25GHz” Under revision of IEE Electronics Letters, 2006.
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9. Loss-Control Feedback
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10. Loss-Control Feedback
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11. Loss-Control Feedback
Control the overall
LC tank’s loss by
changing Gneg
Different signs of the denominator: unstable!
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12. How can we stabilize the LCF loop?
Use a local feedback loop (F)
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13. Transient Behavior of the Proposed LCF
Step Response
Trade-off between power and settling time
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14. Loss-Control Feedback: Implementation
Experimental results
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15. Loss-Control Feedback: Experimental Results
Phase noise
F=2
Stable
F=0
Unstable
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16. Loss-Control Feedback: Experimental Results
Stability over the amplitude tuning range
Measured oscillation amplitude (■)
Phase noise (●)
HD3 (▲)
4- F. Bahmani, E. Sanchez-Sinencio,”A stable loss-control feedback Loop for amplitude regulation of LC Oscillators” IEEE Transactions on Circuit and Systems I, 2006.
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17. A New Q-Tuning Scheme: Why?
To tune the quality factor of an LC filter
VCO-based approach is the best choice
Needs perfect match between the LC filter and LC VCO
Needs a stable amplitude control loop for VCO
The tuning range of Q depends on the VCO amplitude and nonlinearities of the Gneg:
Is there any way to tune Q to an arbitrary value?
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18. LC Filters Q-Tuning An Accurate Automatic Quality Factor Tuning
Scheme for Gigahertz Range LC Filters
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19. LC Filters Q-Tuning Basics of 2nd order LC filter
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20. LC Filters Q-Tuning Basics idea:
Two amplitude locked loop: one at ω0 and the other one at ωL.
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21. LC Filters Q-Tuning
Proposed Scheme
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22. LC Filters Q-Tuning Stability analysis via phase portrait technique
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23. LC Filters Q-Tuning: Implementation
One filter is used to overcome
the mismatch problem
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24. LC Filters Q-Tuning: Multiplier
Self-multiplier
Linearized Gilbert cell
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25. LC Filters Q-Tuning: Experimental Results
Independent tuning of Q and A0
A0(dB)={-15, -10, -5, 0}
Q={60, 80, 120, 220}
Q={50, 60, 70, 120}
A0(dB)=0.
5- F. Bahmani, T. S. Gotarredona, E. Sanchez-Sinencio, ”An accurate quality factor and amplitude tuning scheme for high frequency LC bandpass filters ” submitted to the IEEE Transaction on Circuit and System I, 2006.
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26. Conclusion
A stable amplitude control feedback loop for LC VCO’s is proposed and its application in the VCO-based Q-tuning of LC filters are demonstrated
An accurate Q-tuning scheme for 2nd order active LC filters is presented.
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27. References
F. Bahmani, and E. Sánchez-Sinencio, "A Stable Loss Control Feedback Loop for VCO Amplitude Tuning", IEEE Transaction on Circuits and Systems I: Regular Papers: Volume: 53, Issue 12, pp , Dec
F. Bahmani, E. Sánchez-Sinencio, ”VCO-based quality factor tuning of a second-order LC filter at 2.25GHz” in dissertation
F.Bahmani, T. Serrano-Gotarredona, and E. Sánchez-Sinencio, "An Accurate Automatic Quality Factor Tuning Scheme for 2nd-Order LC Filters", IEEE Transaction on Circuits and Systems I, pp , Vol 54, Issue 4,  April 2007.
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28. Publication
F. Bahmani, E. Sanchez-Sinencio, ”A Low THD, 10.7 MHz Tuned Oscillator Using Positive Feedback And Multilevel Hard Limiter” submitted to the IEE Transaction on Circuits, Devices and Systems, 2006.
F. Bahmani, E. Sanchez-Sinencio, ”A highly Linear 3rd order CMOS Pseudo-Differential Low Pass Filter” to be submitted to the Journal of Solid State Circuit, 2006.
S. W. Park, F. Bahmani, E. Sanchez-Sinencio, ”A 10.7 MHz Linearized Switched-Capacitor Based Oscillator Using the Multilevel Hard Limiter” To be submitted to the IEEE Journal of Solid State Circuit, 2006.
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