Low frequency small signal equivalent circuit model of Bipolar Junction Transistor (BJT)
When signal frequency is low amplitude is small.
Highest frequency is the order of 1014 Hz
So frequency range is 0-1014 Hz
High frequency: -
The signal frequency for which the device capacitances have appreciable effect on the behavior, response or performance of the device is called as high frequency signal.
Low frequency: -
The signal frequency for which the device capacitances have no effect on the behavior, response or performance of the device is called low frequency signal.
iB- total instantaneous value of base current.
Small signal: -
If is the amplitude of the input and output signals are small in comparison to quiescent value voltage and current, they are called small signals.
Large signal: -
If the amplitude of the signal are comparable or large in comparison to the quiescent value of voltage & current, they are called large signal.
Equivalent circuit: -
An electrical circuit (network) which closely approximates the actual behaviour of a semiconductor device under specified operating condition is called equivalent circuit model of the device.
In active region, Ic= βIB
Commonly used transistor equivalent ckt. Produce are of two types:-
(1) remodel: - It is derived from the input and output characteristics of the transistor.
(2) hybrid model