Question

The network formed by resistors and capacitors for modifying the rate of change of gain and the phase shift is called a compensating network. Which of the following statements are not correct ?

(A) The main purpose of a compensating network is to modify the performance of op-amp ciruit over the desired frequency range

(B) There are two types of op-amps : internally compensated and externally compensated

(C) 741 C is an externally compensated op-amp while 709 C is internally compensated op-amp

(D) The phase lag and phase lead are most commonly used compensating networks in op-amps

(E) Phase lag contributes a positive phase angle and phase lead a negative phase angle

Choose the most appropriate answer from the options given below : 

1. (B) and (C) only 
2. (B) and (E) only
3. (C) and (D) only
4. (C) and (E) only

Answer 1

Correct Answer - Option 4 : (C) and (E) only

Compensators are the network that is added to the plant of the system to improve the frequency response characteristic of the system such as magnitude & phase over the desired range of frequencies.

Op-amps are both internally and externally compensated:

• To avoid unintentional creation of positive feedback, which will cause the amplifier to oscillate.
• To improve the bandwidth of the single pole system.

T41C is internally compensated Op-amp whereas T09C is externally compensated Op-amp

Phase lag contributes negative phase angle & phase lead contributes positive phase angle.

Ex: The system having phase ϕ = 70° at ω = 7 rad/sec phase lag of 30° will make it ϕ = 70 – 30 = 40° at same frequency, and phase lead will make it ϕ = 70 + 30 = 100° at same frequency.