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Digitally-Controlled Gm-C Band-pass Filter
G .Jin, H. Chen, C. Gao, Y. Zhang H. Kobayashi, N. Takai, K. Niitsu
(Gunma University) K. Hadidi (Urmia University)
2012 IEEE Asia Pacific Conference on Circuits and Systems
Paper No. 7036
Supported by STARC
Gunma University Kobayashi-Lab
Presented by Guanglei Jin (靳 光磊)
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
3
Outline
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
4
Outline
Wireless LAN, Bluetooth, etc. IF Receiver
5
Background
Gm-C filters are needed
Center frequency & Q-value adjustment is a challenge
6
Research Objective
Fine CMOS process Low voltage
Analog band-pass filter
• Switched Gm-C integrator
• Digital schemes
Center Frequency
Q-value
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
7
Outline
Proposed Switched Gm-C Integrator
)( iiooo VVgmIII
)(2
iio
o VVsC
gm
sC
IV
)(2
iio
o VVsC
gm
sC
IV
iooo VsC
gmVVV
8
Input Voltage Output Current
Gm Cell (OTA)
Gm-C Integrator
Proposed Switched Gm-C Integrator
9
Gm
Ibias
Conventional approach
Proposed method
Analog adjustment of Gm using Ibias
Difficult for fine CMOS with low voltage
Gm
Digital adjustment of Gm by switch
low voltage control
Continuous Adjustment of Switched Gm-C Integrator
10
Noise characteristics C → Constant
Gm → Adjustable
Switched Gm-C Integrator • Low-voltage • Digital control
Continuous Adjustment
Integral Part Adjusting
Switched Gm-C Integrator
11
0
2Gm
Adjust Fractional Part by PWM
12
offon
on
TT
TD
GmDVin
Iout
PWM control
Tr ON
OFF
TON
Switched Gm-C Integrator
1bit ΔΣ converter for high accuracy
Adjust Fractional Part by ΔΣ
1bit ΔΣ converter
13
Switched Gm-C Integrator
Vin
Iout
Input and Output Waveforms of Switched Gm-C Integrator
14
mVVin 500
kHzf 598
pFC 1
SGm 6102/1
Input Voltage Amplitude and Pulse Density with ΔΣ Adjustment
15
0
10
20
30
40
50
60
70
80
0.0 0.2 0.4 0.6 0.8 1.0
Vre
f (m
V)
Pulse Density (×100%)
432221
2
21)(GmGmGmsCCCs
sCGmsH
2
002
0)(
sQ
s
sKsH
21
430
CC
GmGm
2
22
431
GmC
GmGmCQ
431
2
12
GmGmC
GmCK
Gm-C Second-order BPF
16
Gm-C Second-order LPF
432221
2
31" )(GmGmGmsCCCs
GmGm
V
VsH
in
m
2
002
0)(
sQ
s
KsH
21
430
CC
GmGm
2
22
431
GmC
GmGmCQ
421
3
2
1
GmCC
GmGmK
17
Vm
Another node of the filter
VLP
VBP
C
gm
MM
NN
21
430
2
22
431
NM
NNMQ
431
2
12
NNM
NMK
Proposed Digitally-controllable BPF and LPF
18
gmNGm 11
gmNGm 22
gmNGm 33
gmNGm 44
CMC 11
CMC 22
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
19
Outline
Whole Tuning Scheme
20
• Suitable for digital low voltage implement • Require a reference frequency
VLPF
Center Frequency Tuning Part
21
VLPF
Proposed Center Frequency Tuning Method
)(arctan
2 22
0
0
i
i
Q
432221
2
21)(GmGmGmsCCCs
sCGmsH
22
Magnitude characteristics
Phase characteristics
θ=0 Center frequency tuning is done
ω0: Center Frequency ωi: Input Frequency
Principle for Using Phase Characteristics
)(arctan
222
0
0
iQ
i 00①
i 00③
i 00② Done
ω0 is adjusted bigger
ω0 is adjusted smaller
21
430
CC
GmGm
23
Gm3, Gm4 bigger
Gm3, Gm4 smaller
4
Vref = sin(ωot)
Signals of PFD
PFD(Phase Frequency Detector)
24
ω0 is desired center frequency
Comparator
Charge pump
4bitADC
Comparator
BPF
Operation of Charge Pump
Adjust the Gm3, Gm4
values
25
Input and Output Waves of BPF
Vout
Vref
Transient state Adjusted state
26
Phase is aligned
Center Frequency Tuning Simulation Result of BPF
pF59.1CSGm 5105 Simulation parameters
221 NN 121 MM 150 43 NN
27
100kHz 500kHz 300kHz
Center Frequency Tuning Simulation Results of LPF
pF59.1CSGm 5105 Simulation parameters
221 NN 121 MM 150 43 NN
28
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
29
Outline
Q-value Tuning Part
30
VLPF
KQCGm
CGmGm
CGmGm
CGm
Gm
GmH
2
2
2
143
143
2
2
1
2
10 )(proposed method
Fix Center frequency and K
QKjH )( 0
Q-value Tuning Method
31
Q-value is proportional to gain
ω0: Center frequency
ω0 determined by Gm3, Gm4
K determined by Gm1, Gm3, Gm4
21
430
CC
GmGm
2
22
431
GmC
GmGmCQ
421
3
2
1
GmCC
GmGmK
In Case Q is Smaller than Desired Value
32
V1>V2 Vcp is tuned bigger Gm2 is tuned smaller
Q∝(1/Gm2) Q → bigger
ω0 has been adjusted
2
22
431
GmC
GmGmCQ
ω0 has been adjusted
Output of Comparator
33
COMPUP
COMPDOWN
ω0 has been adjusted
Output of Charge pump
34
VCP
ω0 has been adjusted
Output of ADC
35
S1
S2
S3
S4 Q∝(1/Gm2)
In Case Q is Bigger than the Desired Value
36
V1<V2 Vcp is tuned smaller
Q∝(1/Gm2) Q →smaller
ω0 has been adjusted
2
22
431
GmC
GmGmCQ
Gm2 is tuned bigger
AKVQV ref /2 refVV 1
When V1 = V2 A
KQVAKVQ refref
1/
Q → Determined by A
Algorithm of Q-value Tuning
37
K is fixed
ω0 has been adjusted
KQjH )( 0
Input and Output Waves of BPF
Vout
Vref
38
Transient state adjusted state Phase is aligned
Q-value Tuning Simulation Result of BPF
Simulation parameters
pF59.1CSGm 5105
121 MMkHzf 6000
39
Q=6
Q=3
Q=1
Q-value Tuning Simulation Result of LPF
Simulation parameters
pF59.1CSGm 5105
121 MMkHzf 6000
40
Q=6
Q=2
Q=1
• Research Objective
• Switched Gm-C Band-pass Filter
• Center Frequency Tuning
• Q-Value Tuning
• Conclusion
41
Outline
Conclusion
42
• Propose a digitally-controlled Gm-C band-pass filter using switched Gm arrays
Fine CMOS Low voltage
• Digital tuning schemes
Center Frequency Phase property
Q-value Gain property (Center frequency has been adjusted)
• Present SPICE simulation results
Determined by Gm3,Gm4
Determined by Gm2
Orthogonal