- RE: Casode CCS Question - danlaudionut 07:38:57 05/15/09
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- In Reply to: RE: Casode CCS Question posted by humless on May 15, 2009 at 06:31:34
Humless
> > the mu follower output impedance is about 1/gm
> > of the mu-follower mosfet (actually somewhat lower)
I am aware of that but I was wondereing if the cascode
increases the gm factor in the mu follower output.
> > mu-follower does not contribute to the voltage gain
> > (actually, mu follower attenuates the signal about 0.8 times or so)
I would expect ALOT lower signal loss as
most tubes as CF have ~.9 gain ratio and
FETs are known to have higher gm than tubes.
DanL
- RE: Casode CCS Question - humless 18:10:10 05/15/09
(0)
- In Reply to: RE: Casode CCS Question posted by danlaudionut on May 15, 2009 at 07:38:57
Dan,
I apologize for misunderstending,
the answer is cascode does not decrease the effective output impedance,
it does a different thing which I assume you know as well-
in case of p-mos cascode load, the common-gate (CG) mosfet (bottom one) acts as an amplifier of the impedance of the top pmos which formally can be classified as a common-source (CS) config.
One could say the tube anode AC signal leaks though the output impedance of the CG fet (ro) then impedance of the CS fet (ro) to B+. That small leakage current creates an AC voltage between the drain and source of the CS mosfet. The latter is amplified by the CG mosfet and results in large AC voltage at the drain of CG mosfet. Thus, we have small AC current and large AC voltage 0 large output impedance, I dont see how the mu-follower is involved,
Please let me know if I am missing something,
Thanks!
- RE: Casode CCS Question - humless 18:10:10 05/15/09
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