Tuesday, 2 June 2015

Miller's Theorem - Input Capacitance


Please see attached image. I've become confused if the answer to this question, which uses Miller's Theorem is correct as it should not be a minus, rather it should be a plus. Please see my working out.


Thanks


Question Working Out Solution




Answer



In general case the situations look like this


enter image description here


Now let as try to find a input resistance.


Rin = Vin/Iin


In = (Vin - Vout)/R = (Vin - A*Vin)/R = Vin * (1 - A)/R


Rin = Vin/Iin = R/(1 - A)


As you can see we have a "minus" sign. We get the "plus" sign only when our amplifier gain is negative (inverting amplify)


Rin = R/(1 - (-A)) = R/(1+|A|)


No comments:

Post a Comment

arduino - Can I use TI's cc2541 BLE as micro controller to perform operations/ processing instead of ATmega328P AU to save cost?

I am using arduino pro mini (which contains Atmega328p AU ) along with cc2541(HM-10) to process and transfer data over BLE to smartphone. I...