Question

1.If an inverting voltage amplifier with a large gain were built to amplify a small sinusoidal
signal and the output waveform was observed to be sinusoidal but with a much lower
amplitude than predicted by a theoretical analysis assuming an ideal operational amplifier,
what non ideal property of the operational amplifier would be likely contributing to this
degradation in performance?
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Answer 1

Answer

An ideal Op-Amps has the following characteristics:

1. It has infinite input impedance

2. Output impedance is zero and output voltage is independent of the current drawn from the output terminal.

3. Gain is infinite

4. If input voltage V is zero, than output voltage V0 is also zero.

5. It has infinite bandwidth.

6. Characteristics do not drift with temperature.

But in Prac in Practical Op-Amps :

All the infinite parameters and zero parameters specified above, have finite values.

The equivalent circuits of an ideal and non-ideal Op-amps are shown in the below diagram

The various other parameters of practical Op-Ampss are:

1. Finite gain (Ad) With differential input and common mode gain (A).

   Thus the common mode rejection ratio CMRR IAd/Acl will be finite.

   Large values of CMRR are desired. For an ideal Op-Amps, CMRR is infinite.

2. Finite Bandwidth" Gain drops regularly with increasing frequency.

3. Slew-rate" Slew rate limitations arise because the transistors inside the Op-Amps are unable to provide sufficient current to rapidly charge capacitive loads. The slewrate also depends on the external circuitary connected to the OA. Usually, the worst case occurs when the OA is connected as a unity gain amplifier.

4. Input bias current is finite.

5. Input offset current is finite.