Op-Amp Example 1

 Determine the output voltage in the following cases for open-loop differential amplifier.

Case 1:  V_in1 = 5uV dc and V_in2 = -7 uV dc

Case 2: V_in1 = 10mV rms and V_in2= 20 mV rms

Consider A=2,00,000 , R_i = 2Mohm, R₀=75 ohm, +V_cc= +15 V, -V_ee=-15 V and output voltage swing = ±14V.

Do comment on output.

 Answer:

Now as per the equation of Voltage gain

 

Now For Case 1

 

Now For Case 2

 

The theoretical value of output is -2000 V rms. However, the op-amp saturates at ±14 V. Therefore, the actual output waveform will be clipped.

This situation is unacceptable in amplifier applications. The normal solution to this problem is to use negative feedback.