mosfet in the ‘triode’ region (revisiting)
DESCRIPTION
MOSFET in the ‘Triode’ region (revisiting). MOSFET in the ‘Triode’ region. FYI, if you want to make precise evaluations, it is necessary to use a more complete formula than the simplistic model: Still an approximation …. MOSFET in the ‘Triode’ region. Series expansion around 0 for Vs and Vd:. - PowerPoint PPT PresentationTRANSCRIPT
YLD 10/2/99 ESINSA- 1 -
MOSFET in the ‘Triode’ region(revisiting)
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 ….
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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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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Transconductor - C
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Transconductor - C
gm CVin Vout
Iout
The integrator based on a transconductance:
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Transconductor?
Vin
Iout
0
)1(
out
in
inout
Z
RZ
RVI
R
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Linear transconductance?
)( q
inout
Ifunction
termsnonlinearVI
Iq+Iout Iq-Iout
2xIq
Vin -Vin
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Linear transconductance
2121 2 VVVkII C
I1 I2
I1+I2
V1 V2
Vc Vc
2tsgds VVVkIMOSFET
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Linear transconductance
Iq1+Iq2+Iout Iq1+Iq2-Iout
V1 V2
2xIq1 2xIq2 > 2xIq1
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Linear transconductance
Iq+Iout
Vin
Iq
Iq-Iout
-Vin
Iq
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Linear transconductance
Vin/2
Iq+Iout
Iq
Iq-Iout
-Vin/2
Iq
Vb
Degenerating the sources
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Linear transconductance
Vin/2 -Vin/2Vb1
Vb2
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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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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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Resistor
-gm
R
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Balanced Resistor
gmR
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Variant Using Gyrators
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Gyrator
r
rGwith
VGi
VGi
112
21
V1 V2
i1 i2
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Inductance?
r
dt
diCrV
dt
dVCi
rGwith
VGi
VGi
121
22
12
21
1
V1 V2
i1 i2
Inductance!
C
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Practical Realization of a Gyrator
gm
gyrator
r
-gmV1 V2
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Balanced Gyrator
gm gm
gyrator
r
Minus Sign is here !
V1 V2
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A few applications of the Gyrator
r r
L/r 2
L
L
r
L/r 2
Capacitance !!!
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r r
L/r 2
L
C
Etc..
C
A few applications of the Gyrator
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An Example: RLC Filter
R L2
C1
C2
C3 R
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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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Example
-gm
gm gm
-gm
gm
-gm -gmC1 C3
C2
L2/r2
R L2
C1
C2
C3 R
(mapping)
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ExampleR L2
C1
C2
C3 R
Balanced version:
r r
L2/r 2
Vin/R
2C2
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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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Tuning the Transconductor - C
Vin/2 -Vin/2
TuningM1
C-Vout/2 Vout/2
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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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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.