General block diagram of an opamp in a negative feedback configuration:

 

 

Voltage at the inverting input terminal:

V-_in = V₁ + kV_out

 

Output voltage:

V_out = -A_v(s) V-_in

 

Voltage gain:

A_vf   ... closed-loop gain

A_v    ... open-loop gain

kA_v  ... loop gain

 

Supposing the open-loop gain in the form:

 

Poles s_i are assumed due to stray capacitances to ground in an otherwise resistive circuit.

For s = jw, A_v(jw) gives the frequency response of the opamp.

 

Magnitude:

 

 

Phase:

 

Both, magnitude and phase are monotone decreasing functions of w.