ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: R.G. I'm taking a class this week, and t... -- 4/6/1998 4:35 PM

Re: Soft clipping, CMOS and the Muff

4/8/1998 5:01 AM
MHelin	Re: Soft clipping, CMOS and the Muff R.G. wrote: n a CMOS gate used as a feedback amp, the input impedance is astronomical. Therefore you can predict almost exactly what the current in the feedback path is, no matter what it is. The current at any point is Vin/Rin. In standard opamp (summing) inverter, the input impedance is the same as the value of the input resistor. If you increase this resistor value, the impedance will increase and the current through it will decrease, as well as the current through the feedback resistor. Is this what you mean? So when you increase the feedback resistor, the current doesn't change, only the voltage swing at the output. This is how an amplifier works. Difference with diodes in feedback is just that their resistance is not constant, but when the output goes above 0.6V the diode is clipping. What makes CMOS inverter work differently (I think) is that it's not a linear amplifier itself, and even the clipping diodes can't keep it in linear region. -mikko

4/8/1998 5:01 AM

MHelin

Re: Soft clipping, CMOS and the Muff

R.G. wrote:

n a CMOS gate used as a feedback
amp, the input impedance is
astronomical. Therefore you can predict
almost exactly what the current in the
feedback path is, no matter what it is.
The current at any point is Vin/Rin.

In standard opamp (summing) inverter, the input impedance is the same as the value of the input resistor. If you increase this resistor value, the impedance will increase and the current through it will decrease, as well as the current through the feedback resistor. Is this what you mean? So when you increase the feedback resistor, the current doesn't change, only the voltage swing at the output. This is how an amplifier works. Difference with diodes in feedback is just that their resistance is not constant, but when the output goes above 0.6V the diode is clipping. What makes CMOS inverter work differently (I think) is that it's not a linear amplifier itself, and even the clipping diodes can't keep it in linear region.

-mikko

Replies:

R.G. I think I adjusted the content leve... -- 4/8/1998 8:01 AM