(1) The input stage is composed of a differential amplifier circuit to improve the input resistance, reduce the zero drift, and obtain a higher CMRR.
(2) The intermediate amplifier stage is composed of multiple directly coupled voltage amplifiers to obtain higher voltage amplification.
(3) The output stage is composed of emitter output device or complementary push-pull circuit to reduce the output resistance, improve the output power and load capacity.
(4) Bias circuit to provide suitable and stable static operating point.
3. Two important characteristics of an ideal operational amplifier
(1) Virtual shortness
The potential difference between the two input terminals of an ideal operational amplifier approaches zero.
(2) Virtual break
The two input current of an ideal operational amplifier is zero.
4. Typical circuit of ideal operational amplifier
(1) inverting proportional operation circuit
(2) In-phase proportional operation circuit (voltage follower)
(3) inverse summation circuit