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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 - PowerPoint PPT Presentation
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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)
2 Courtesy of Faramarz Bahmani
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 Courtesy of Faramarz Bahmani
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
4 Courtesy of Faramarz Bahmani
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
5 Courtesy of Faramarz Bahmani
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 Courtesy of Faramarz Bahmani
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
7 Courtesy of Faramarz Bahmani
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
8 Courtesy of Faramarz Bahmani
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.
9 Courtesy of Faramarz Bahmani
Loss-Control Feedback
10 Courtesy of Faramarz Bahmani
Loss-Control Feedback
11 Courtesy of Faramarz Bahmani
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
12 Courtesy of Faramarz Bahmani
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
13 Courtesy of Faramarz Bahmani
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
14 Courtesy of Faramarz Bahmani
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
15 Courtesy of Faramarz Bahmani
Loss-Control Feedback: Experimental Results
2F
F=0
Unstable
F=2
Stable
• Phase noise
16 Courtesy of Faramarz Bahmani
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.
17 Courtesy of Faramarz Bahmani
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?
18 Courtesy of Faramarz Bahmani
LC Filters Q-Tuning
An Accurate Automatic Quality Factor Tuning Scheme for Gigahertz Range LC Filters
19 Courtesy of Faramarz Bahmani
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
20 Courtesy of Faramarz Bahmani
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.
21 Courtesy of Faramarz Bahmani
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
22 Courtesy of Faramarz Bahmani
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
23 Courtesy of Faramarz Bahmani
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
24 Courtesy of Faramarz Bahmani
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
25 Courtesy of Faramarz Bahmani
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.
26 Courtesy of Faramarz Bahmani
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.
27 Courtesy of Faramarz Bahmani
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 Courtesy of Faramarz Bahmani
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.