Description:
The heart of a power
amplifier is the differential amplifier. Basically, it consists
of 2 Class A amplifiers configured to mirror each other,
resulting in potentially excellent Common Mode Rejection.
The beauty of the
diff-amp is that it has 2 inputs, and 2 outputs, and the input
signals can be configured as either inverting or non-inverting.
Current source
maintains the same amount of current for each transistor in
order to maintain the same output balance and insure good CMRR.
(Current Mode Rejection Ratio)
Operation:
The ideal diff-amp has
infinite voltage gain and input impedance.
It is called ‘differential’ because outputs are
always the difference of each output.
For example: Id IC1 increase IC2 decreases
proportionally. Basically
those are an inputs comparators of In 1 and In 2.
J-FETS as diff-amp main
characteristics are higher input impedance and immunity to base
current matching required in bipolar stages.
