1 courtesy of faramarz bahmani lc voltage control oscillator aac a stable loss-control feedback loop...

1 Courtesy of Faramarz Bahmani

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

ECE 665 (ESS)


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.


LC Filters

• Active LC filtersThe 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.

ECE 665 (ESS


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.

Filter

Slave

Filter

Master

Control

Tuningreference

Input Output

Filter

Slave

Control

Tuningreference

Input Tuning OutputTunign

Input Signal Output Signal

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


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.


VCO-Based Q-Tuning• Principle of Operation

– VCO: Large signalinG

S la v e F ilt e r

inv

L

LR

C

couplingC

A m p litu d eC o n tro l

L o o p

L

LR

C

L

LR

C

M a ste r V C O

negG negG

negG

03

,01

;331

aaout

vaout

vaneg

Gi

013 231

2

2

out

outout

Pout vLCdt

dvv

C

a

C

Ga

dt

vd

PP

s

s

sout

Gafora

GaA

A

tωAv

13

1

0

,3

2

:as found becan amplituden oscillatio

statesteady the),sin(If


VCO-Based Q-Tuning

L

C

AaQ

sfilterslave 2

33

4

:regime signal smallin operating

filter, slaved For the

inG

S la v e F ilt e r

inv

L

LR

C

couplingC

A m p litu d eC o n tro l

L o o p

L

LR

C

L

LR

C

M a ste r V C O

negG negG

negG


VCO-Based Q-Tuning

• Experimental results

15mA :Current

1.8V :Supply

0.144mm :Area

m0.35 TSMC2

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.


Loss-Control Feedback



• Control the overallLC tank’s loss by

changing Gneg

Int

s

Int

ENVs

Int

s

refA

sA

s

A

sA

sAsH

22

2

)(

)()(

2

• Different signs of the denominator: unstable!

negGG

ItA

tank

bias)(

:amplituden Oscillatio

re fA

en vV

)co s()()( 0 ttAtV o

CV

ddV

Ints1

)(

detector

Envelop

envbiasI

tankG

negG


How can we stabilize the LCF loop?• Use a local feedback loop (F)

Int

sENVs

Int

REFInt

s

As

AFs

sAA

sA

221

)(2

)(2

)

re fA

en vV

co s()()( 0 ttAtV o

F

detector

Envelop

Ints1

VCO

CV

3.1 :VCO LC typicalaFor 2

:trequiremenStability

critical

ENVscritical

F

AFF


Transient Behavior of the Proposed LCF• Step Response• Trade-off between power and settling

time 0)(

2

102

1

AtA

C

G

A

A

A

A

dt

d

loop

m

Int

Detector

Envelope

1mG

)(tvenv

refvevcv

loopC

2

1

mG

LCnegG

lossR

VCO

1

2

m

m

G

GF


Loss-Control Feedback: Implementation

ENVC

refout AV or

refenv VV or

1ME 2ME

3ME 4ME

biasI

refout AV or

ddV

ddV

L L

4M3M

Mtail

detector

Envelop

detector

EnveloprefA

CV

loopC1mG

2mG

outV outV

C C

fV

envV

refV

LPF

1

2

m

m

G

GF

8mA :Current

2.8V :Supply

0.046mm :Area

m0.35 TSMC2

• Experimental results


Loss-Control Feedback: Experimental Results

2F

F=0

Unstable

F=2

Stable

• Phase noise


Loss-Control Feedback: Experimental Results

40

30

-35

-33

-31

-29

-27

-25

-23

1.4 1.6 1.8 2 2.2 2.4 2.6

Bias voltage of the VCO tail current source [V]

Os

cil

lati

on

am

pli

tud

e [

dB

m]

-120

-115

-110

-105

-100

-95

Ph

as

e n

ois

e @

1M

Hz

[dB

c/H

z]

- 40

- 42

- 44

- 46

- 48

- 50

HD

3 [d

B]

Measured oscillation amplitude (■)Phase noise (●) HD3 (▲)

• Stability over the amplitude tuning range

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.


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:

L

C

AaQ

sfilterslave 2

33

4

• Is there any way to tune Q to an arbitrary value?


LC Filters Q-Tuning

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


LC Filters Q-Tuning

L L

1M

2M 3M4M 5M

6M

inVinV

ddV

C C

outV

gmV qV

fV TqqP

Tgmm

negP

m

VVG

VV

GG

GA

2

0

)(

1

TqqP VVGL

CQ

• Basics of 2nd order LC filter

20

02

00

)(

)()(

sQ

s

sQ

A

sV

sVsH

in

o


LC Filters Q-Tuning

0

0

1

1

2

1

2

11

L

L

Q

Q

)1(2

)( 0 jA

jH L

00 A)H(jω

2/A)H(jω)H(jω 0HL

Lω Hω0ω

BW 3dB-

• Basics idea:

• Two amplitude locked loop: one at ω0 and the other one at ωL.


LC Filters Q-Tuning

fV qV gm

V

0fV

tcosV 00

tco sVA 000

L P F

dA/1

L P F

dA

VA

2

200

tVA 022

00 cos Tuning Amplitude

1 Loop

2

20V

aerror

t2sin

2

1tcos LL

2

2

tcosV LL

tsintcosA

LL0 LV

fV qV gm

V

0fV

0

2

A 2LV

L P F

dA/2

L P F FB

d

L

A

VA

2

20

Tuning-Q

2 Loop

2

2LV

qerror

Loop Tuning Amplitude Loop TuningFactor Quality

• Proposed Scheme


LC Filters Q-Tuning• Stability analysis via phase portrait technique

)2

1(

)2

1()11

1

4

(

0

0

22

uA

vKv

uA

v

K

K

uLQC

uAv

Ku

d

dLm

q

d

dL

)(2

11

:point mEquilibriu

00

0

TqqPm

dTgm

dP

qTq

VVGA

VV

L

C

QGVV


LC Filters Q-Tuning: Implementation

5mA :Current

1.3V :Supply

0.073mm :Area

m0.35 TSMC2

• One filter is used to overcome the mismatch problem

fV qV gm

V

L P F

dA/1

L P F

CHIP

OFF


LC Filters Q-Tuning: Multiplier

1R 2R

3R 4R

RC R C

1M 2M

3M 4M

5M

1bM

6M

7M 8M 9M

2bM 3bM4bM

11M 1 2M

L P F L P F

10M

inV inVinV

inV

outv outv

biasV

bleedingI

• Self-multiplier– Linearized Gilbert cell

)cos( tA 2

2A

tMeasuremen

:Circles

Simulation

:line


LC Filters Q-Tuning: Experimental Results

A0(dB)={-15, -10, -5, 0} Q={60, 80, 120, 220}

Q={50, 60, 70, 120} A0(dB)=0.

• Independent tuning of Q and A0

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.


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.


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.

http://amsc.tamu.edu/SIS/Publications/pub/jounal/2006_18.pdf





Publication7. 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.

8. 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.

9. 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.

1 courtesy of faramarz bahmani lc voltage control oscillator aac a stable loss-control feedback loop...

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