This is the solution to a practice assignment of the subject basic electronics, of the topic op amps and diodes from my college.

1. Basic Electronics (ECE113)
Assignment 4_Solutions (40 marks)
Q1. The op amp shown in Figure 1 has an input bias current of 90 nA at C. Calculate (a) the
20
0
voltage gain and (b) the output offset voltage due to the input bias current. 4 marks (2+2)
Fig.1
Ans1:

2. Q2. Determine (a) the value of the feedback resistor and (b) the frequency for an inverting
amplifier to have a voltage gain of 45 dB, a closed-loop bandwidth of 10 kHz and an input
resistance of 20 k. 4 marks (2+2)
Ans2:

4. Q3. A steady voltage of −1.25 V is applied to an op amp integrator having component values of
R=125 k and C =4.0μF. Calculate the value of the output voltage 120 ms after applying the
input, assuming that the initial capacitor charge is zero. 4 marks
Ans3:

5. Q4. In the differential amplifier shown in Fig. 4, determine the output voltage, Vo, if: (a) V1 =4
mV and V2 =0, (b) V1=40 mV and V2 =30 mV, (c) V1 =25 mV and V2 =40 mV.
3 marks (2+2+1)
Fig.4
Ans4:

6. Q5. Derive the transfer function for the circuit shown in figure 5. Find the high frequency gain
and the cutoff frequency (2 marks upto here). Design the circuit to obtain a high frequency
gain of 20 dB, 3 dB cutoff frequency of 10 kHz and a high frequency input resistance of 1 K (2
marks upto here). What is the unity gain bandwidth of this amplifier? (1 marks upto here)
Fig.5 5 marks (2+2+1)
Ans5:

9. Q6. Derive an expression for the input resistance of the inverting amplifier of Figure 6 taking into
account the finite open-loop `gain, A of the op-amp. 4 marks
Fig.6
Ans6:

12. Q7. The switching circuit of Fig. 7 contains two silicon diodes. For switch S closed, estimate 𝐼𝑎
and for
𝐼𝑏
𝑉𝑎
= − 1, − 0. 1, + 1 & + 2 𝑉.
(a) For switch S open, estimate and for 4 marks (2+2)
𝐼𝑎
𝐼𝑏
𝑉𝑎
= + 1 𝑉.
Fig.7
Ans7:

15. Q8. A common application of silicon diodes is shown in Fig.8. Predict as a function of
𝐼2
𝑉1
Fig. 8 4 marks
Ans8:

16. Q9. Consider the silicon diode circuits of Fig. 9 (a & b). Let 𝑉1
= 5𝑉, 𝑉2
= 0, 𝑉𝑐𝑐 = 6𝑉.
Determine for both (a) & (b).
𝑉𝑜
Fig.9
4 marks (2+2)
Ans9:

17. ●
Q10. Zener diode shown in Figure 10 has a breakdown voltage ( ) of 6 V. It is used in a
𝑉𝑍
voltage regulator circuit to regulate the output voltage. If = 2.5 kΩ, find the output voltage,
𝑅𝐿
power dissipation across the Zener diode and the load resistance . If the value of is
𝑅𝐿
𝑅𝐿
changed to 4 kΩ, find the power dissipation across the Zener diode. 4 marks (3+1)

18. Fig.10
Ans10