Test: Differential Amplifiers - Electronics and Communication Engineering (ECE) MCQ

The aiven circuit is redrawn as shown below.

Writing loop equation containing two diodes and

The goal of designing differential amplifiers is to minimize the effect of common-mode input signal and amplify the difference of the voltages between the two input lines.

The net output resistance is: R_L’ = 40k ||10k = 8 k

Output voltage : - 50i_b.(8k)

Input voltage : i_b.(1k)

In single stage differential amplifier, the output offset voltage is basically dependent on the mismatch of I_B and β.

The values of h_FE, V_BE and I_CB0 vary with temperature and due to the variation in any of these quantities the output voltage may change which may not be distinguished from a change in the input signal voltage, Due to this reason it is not so easy to design d.c. amplifiers using transistors. Hence, both assertion and reason are true and reason is the correct explanation of assertion.

Assertion is not true because “figure of merit” (or CM MR) of a differential amplifier is to reject a common mode signal (v_C).

we know that

Now,

From equation (iii) and (iv), the percentage difference in output voltage obtained for the two sets of input voltages

Also

Hence, both transistors of the differential amplifier are biased at a Q-point having l_B = 1.09 μA and V_c=7.9V.