Q. Show the Frequency response of Rc Coupled Amplifier?
1. At low frequency i.e,less than 50 Hz reactance of Cc is going high hence same part of the signal will pass from one stage to next stage.CE cannot shunt RE because of its large reactance at low frequency.These factors cause falling of voltage gain.
2. At higher frequencies i.e, greater than 20 kHz reactance of Cc is very small and it behaves as a short circuit.This increase the loading effect of the next stage and reduces the voltage gain.At high frequencies, the capacitive reactance of base-emitter is very low which increases the base current.So b reduces and voltage gain drops off.
3. At mid frequency i.e, 50Hz to 20kHz ,the voltage gain is constant.Cc in this frequency range is such as to maintain a uniform voltage gain.Thus as frequency increases reactance of Cc decreases that tends to increase the gain.However lower reactance means higher loading of first stage and hence lower gain.So the two factors cancel each other resulting in a uniform gain at mid frequencies.