Electric Circuits and Networks

6.4 NEGATIVE FEEDBACK IN OPERATIONAL AMPLIFIER CIRCUITS

Consider the circuit in Fig. 6.4-1(a). We ignore the offsets in output in our analysis in this section. Therefore, the output in the circuit in Fig. 6.4-1(a) is given by v_o = A(v_l – v₂), where A is the differential mode voltage gain of the Opamp. The value of A for μA 741 Opamp is around 250,000. Let us assume that the power supply used is ±12 V in all the three circuits. The voltage saturation levels will be taken approximately equal to the supply voltage of 12 V. Actually, it is 10.6 V and – 11 V; we ignore the difference.

Hence, the first circuit will saturate when the differential input voltage v_d = v₁ – v₂ goes out of the range (–48 μV, +48 μV). We usually do not need this much of gain. ...