MOSFET in the ‘Triode’ region (revisiting)
description
Transcript of MOSFET in the ‘Triode’ region (revisiting)
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YLD 10/2/99 ESINSA- 1 -
MOSFET in the ‘Triode’ region(revisiting)
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YLD 10/2/99 ESINSA- 2 -
MOSFET in the ‘Triode’ region
2323
22
2232
21
2
fbsfbd
bsbd
sdffbbg
ox
VVVV
VVVV
VVVVV
LWCId
FYI, if you want to make precise evaluations, it is necessary touse a more complete formula than the simplistic model:
Still an approximation ….
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YLD 10/2/99 ESINSA- 3 -
isidisdsd VVaVVaVVaId ...22
21
Series expansion around 0 for Vs and Vd:
MOSFET in the ‘Triode’ region
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YLD 10/2/99 ESINSA- 4 -
232
1
1
233
212
211
22!
52...5311
...
2241
24121
22
ifBi
ioxi
fox
fox
fffbgox
Vi
iLWCa
VbLWCa
VbLWCa
VbVVLWCa
MOSFET in the ‘Triode’ region
small
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YLD 10/2/99 ESINSA- 5 -
Transconductor - C
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YLD 10/2/99 ESINSA- 6 -
Transconductor - C
gm CVin Vout
Iout
The integrator based on a transconductance:
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YLD 10/2/99 ESINSA- 7 -
Transconductor?
Vin
Iout
0
)1(
out
in
inout
Z
RZ
RVI
R
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YLD 10/2/99 ESINSA- 8 -
Linear transconductance?
)( q
inout
Ifunction
termsnonlinearVI
Iq+Iout Iq-Iout
2xIq
Vin -Vin
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YLD 10/2/99 ESINSA- 9 -
Linear transconductance
2121 2 VVVkII C
I1 I2
I1+I2
V1 V2
Vc Vc
2tsgds VVVkIMOSFET
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YLD 10/2/99 ESINSA- 10 -
Linear transconductance
Iq1+Iq2+Iout Iq1+Iq2-Iout
V1 V2
2xIq1 2xIq2 > 2xIq1
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YLD 10/2/99 ESINSA- 11 -
Linear transconductance
Iq+Iout
Vin
Iq
Iq-Iout
-Vin
Iq
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YLD 10/2/99 ESINSA- 12 -
Linear transconductance
Vin/2
Iq+Iout
Iq
Iq-Iout
-Vin/2
Iq
Vb
Degenerating the sources
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YLD 10/2/99 ESINSA- 13 -
Linear transconductance
Vin/2 -Vin/2Vb1
Vb2
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YLD 10/2/99 ESINSA- 14 -
Transconductor - C
Vin/2
Iq+Iout
Iq
Iq-Iout
-Vin/2
Iq
Vb
Iout
M1 M2
M3
C
Iout
CMFB
-Vout/2 Vout/2
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YLD 10/2/99 ESINSA- 15 -
Transconductor - C
Vin/2
Iq
-Vin/2
Iq
Vb
Iout
M1 M2
M3
CIout
CMFB
-Vout/2 Vout/2
Common ModeFeedback
TransconductanceTuning
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YLD 10/2/99 ESINSA- 16 -
Resistor
-gm
R
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YLD 10/2/99 ESINSA- 17 -
Balanced Resistor
gmR
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YLD 10/2/99 ESINSA- 18 -
Variant Using Gyrators
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YLD 10/2/99 ESINSA- 19 -
Gyrator
r
rGwith
VGi
VGi
112
21
V1 V2
i1 i2
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YLD 10/2/99 ESINSA- 20 -
Inductance?
r
dt
diCrV
dt
dVCi
rGwith
VGi
VGi
121
22
12
21
1
V1 V2
i1 i2
Inductance!
C
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YLD 10/2/99 ESINSA- 21 -
Practical Realization of a Gyrator
gm
gyrator
r
-gmV1 V2
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YLD 10/2/99 ESINSA- 22 -
Balanced Gyrator
gm gm
gyrator
r
Minus Sign is here !
V1 V2
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YLD 10/2/99 ESINSA- 23 -
A few applications of the Gyrator
r r
L/r 2
L
L
r
L/r 2
Capacitance !!!
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YLD 10/2/99 ESINSA- 24 -
r r
L/r 2
L
C
Etc..
C
A few applications of the Gyrator
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YLD 10/2/99 ESINSA- 25 -
An Example: RLC Filter
R L2
C1
C2
C3 R
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YLD 10/2/99 ESINSA- 26 -
ExampleR L2
C1
C2
C3 R
r r
L2/r 2
Vin/RC3C1
C2
RR
r r
L2/r 2
Vin
C2
C3C1R
R
mapping
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YLD 10/2/99 ESINSA- 27 -
Example
-gm
gm gm
-gm
gm
-gm -gmC1 C3
C2
L2/r2
R L2
C1
C2
C3 R
(mapping)
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YLD 10/2/99 ESINSA- 28 -
ExampleR L2
C1
C2
C3 R
Balanced version:
r r
L2/r 2
Vin/R
2C2
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YLD 10/2/99 ESINSA- 29 -
Example
2C2
R L2
C1
C2
C3 R
C1 C32gm gm 2gm gm gm gm
2C2
2gmL2/r 2
Balanced version:
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YLD 10/2/99 ESINSA- 30 -
Tuning the Transconductor - C
Vin/2 -Vin/2
TuningM1
C-Vout/2 Vout/2
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YLD 10/2/99 ESINSA- 31 -
Transconductor - C
Same care has to be taken as for other continuous time filters.
Distortion and dynamic range are the major concerns.For high speed modules, bandwidth of the transconductorwill interfere with the transfer function.
Reserve Transconductor-C, like MOSFET-C, to high speedfilters. Do not expect great precision.
It is not yet clear which one will supersede the other, or ifthey will coexist.
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YLD 10/2/99 ESINSA- 32 -
Conclusion: Integrated Filters
Very hot topics.
DSP is taking a huge share in the filters. More and more.
Still, analog to digital and digital to analog converters areprocessing samples. Analog filtering cannot be avoided.
Performances demand is increasing every year.There is no reason that this trend will change in the future.