LC Voltage Control Oscillator AAC

1
LC Voltage Control Oscillator AAC
ECE 665 (ESS)

• A Stable Loss-Control Feedback Loop to Regulate
  the oscillation Amplitude of LC VCOs

Problem Previously reported AAC loops use a
conditionally stable negative feedback
loop Motivation To propose a practically stable
negative feedback loop
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.

3
LC Filters
ECE 665 (ESS

• 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.

4
LC Filters Q-Tuning

• Tuning techniques
• Direct tuning Self-tuning
• Filter is the plant in the tuning system
• Tuning accuracy doesnt rely on matching.

• Indirect tuning master-slave
• VCF-based Master is a filter
• VCO-based Master is a VCO

5
LC Filters Q-Tuning

• VCF-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.

6
VCO-Based Q-Tuning

• Principle of Operation
• VCO Large signal

7
VCO-Based Q-Tuning
8
VCO-Based Q-Tuning

• Experimental results

Q50, 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.
9
Loss-Control Feedback
10
Loss-Control Feedback
11
Loss-Control Feedback

• Control the overall
• LC tanks loss by
• changing Gneg

• Different signs of the denominator unstable!

12
How can we stabilize the LCF loop?

• Use a local feedback loop (F)

13
Transient Behavior of the Proposed LCF

• Step Response
• Trade-off between power and settling time

14
Loss-Control Feedback Implementation

• Experimental results

15
Loss-Control Feedback Experimental Results

• Phase noise

F0 Unstable
F2 Stable
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.
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?

18
LC Filters Q-Tuning

• An Accurate Automatic Quality Factor Tuning
• Scheme for Gigahertz Range LC Filters

19
LC Filters Q-Tuning

• Basics of 2nd order LC filter

20
LC Filters Q-Tuning

• Basics idea

• Two amplitude locked loop one at ?0 and the
  other one at ?L.

21
LC Filters Q-Tuning

• Proposed Scheme

22
LC Filters Q-Tuning

• Stability analysis via phase portrait technique

23
LC Filters Q-Tuning Implementation

• One filter is used to overcome
• the mismatch problem

24
LC Filters Q-Tuning Multiplier

• Self-multiplier
• Linearized Gilbert cell

25
LC Filters Q-Tuning Experimental Results

• Independent tuning of Q and A0

A0(dB)-15, -10, -5, 0 Q60, 80, 120, 220
Q50, 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.
26
Conclusion

• A stable amplitude control feedback loop for LC
  VCOs 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.

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.
  2498-2506, Dec. 2006.
• 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,
  pp745-756, Vol 54, Issue 4,  April 2007.

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.