I was reading about negative feedback circuit specifically amplifier circuits with negative feedback, how these circuit works and how I can use the concept as well as the circuit. Negative feedback improves gain stability, improves input and output impedance(input impedance is high, output impedance is low), and improves non-linear distortion. I noticed that a BJT transistor based two stage amplifier with negative feedback is a non-inverting amplifier. Normally non-inverting amplifier refers to amplifier built with operational amplifier which essentially means that the non-inverting amplifier are built with differential amplifier because inside op-amp differential amplifier built with transistors are used. But here the simple two stage amplifier with negative feedback performs the same task as the op-amp based non-inverting amplifier.
The output signal is bit shifted in phase w.r.t input signal. This is due to the fact that the input signal gets inverted, that is, its gets phase shifted by 180 degree. Then again it gets phase shifted by 180 degree due the second CE BJT amplifier circuit. See phase shifter circuit using op-amp and phase shifter circuit diagram for more on phase shifter circuits.
This means that we can say that the circuit is non-inverting op-amp amplifier or that the BJT transistor based two stage amplifier with negative feedback circuit is an op-amp.
