Test: Operations Amplifier - Electronics and Communication Engineering (ECE) MCQ

Compensation capacitor in the internal structure of op-amp to improve its frequency response, increasing its stability. It also decreases the slew rate of the op-amp.

The internal structure of an op-amp uses a compensation capacitor for stability purpose. It provides dominant pole compensation; thereby the op-amp remains stable. However, the op-amp gain remains constant at low frequencies but decreases at high frequencies due to a compensation capacitor.

CMRR = 20 log(AD/ACM) = 20 log(4000×12/V_ocm) = 100
Log(48000/V_OCM) = 5
48000/V_OCM = 105
V_OCM = 0.48V.

B2 = B1(1+βA) = 10(1+β10⁶) = 100k
1 + β10⁶ = 10k
β = 9.999×10^-3
In percentage, feedback β = 0.99% negative feedback.

The correct block diagram is

The 3dB frequency is the cut-off frequency, where the gain is 1√2 of the maximum. The gain is only constant for infinite frequency, that is, has infinite bandwidth if the op-amp is ideal, which practically doesn’t exist. The UGB is the point at which the gain of op-amp reaches 1.

UGB = A_OLf_OL
f_OL = 10M/2×10⁶ = 5Hz
The AC gain |A| = 
|A| = 2×10⁶/400 = 5000.

dV_OUT(max)/dT =< Slew rate
A.Vmω =< 1.5 V/μsec
10³.5.10^-3.ω = < 1.5×10⁶
ω=<0.3×10⁶
Frequency f = 0.0477×10⁶Hz.

For an ideal op-amp, the open loop voltage gain is infinite. The output resistance is 0 and the input resistance is infinite. Op-amp has zero input current, zero offset voltage, infinite bandwidth, infinite CMRR and infinite slew rate.

Operational amplifier is a high voltage gain, direct coupled amplifier which can be used to perform mathematical operations on analog signals. It can be used to amplify both DC and AC signals.