[SOLVED] Frequency Response & Compensation of Differential Amplifier with BJTs

[pavan garate]

Hi everyone..

Can anyone explain me the Frequency Response & Compensation of Differential Amplifier constructed with BJTs ?

Please suggest me some good links..

 

[Audioguru]

An amplifier has transistors that have some capacitance and wiring also has some capacitance. The capacitance causes a phase shift at high frequencies.
An amplifier usually has negative feedback to reduce its very high gain to a useable amount and to reduce its distortion. The phase shift at a high frequency causes the negative feedback to become positive feedback which causes the amplifier to oscillate at a high frequency.
So a frequency compensation capacitor is added to the circuit of the amplifier (or opamp) to reduce the gain at high frequencies so the gain is less than 1 at a high frequency where the phase shift will cause oscillation. Then the amplifier has a frequency response that drops at high frequencies when it does not have any negative feedback, or its frequency response will be flat up to a certain frequency then drop at higher frequencies if it has negative feedback.

It is easy to see the frequency compensation on the open-loop (no negative feedback) frequency response graph on the datasheet of any opamp.
Look in Google for Frequency Compensation Capacitor.