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# Important Interview Analog Circuits Questions

The article contains analog circuits questions and answers on Resistor networks, transistor MOSFET, current mirror, Opamp, and RC circuits.

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1. Compare the output characteristics of transistor BJT (Bipolar Junction Transistor) and FET (Field Effect Transistor) and also mark the different regions of operations on the characteristics.
2. Given the following RC circuit. Plot the output waveform for the given input based on the given two conditions.
1. τ = RC >> T
2. τ = RC << T

3. For the given DAC(Digital to Analog Circuit) circuit shown in the figure. Calculate the value of Vout for the digital input  D3D2D1D0 = 1010. if Vref =8V.

4. Find the minimum value of voltage Vx for which the maximum current flows through the resistor R. Assume Vth = 400mV and µnCox = 250.

5. Determine the value of voltage Vout for the given following circuit. What is the possible application of this circuit?

6. Refer to the following circuit and draw the output waveform VA and VB for the given square wave input.

7. Among the following circuits which circuit has the higher output impedance? and Why?

8. Find the voltage Vx for the below circuit. Given µnCox = 100 and Vth = 1V.

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9. For the given opamp circuit below, if the initial voltage across the capacitors C1 and C2 are 1V and 3V respectively. Find the output voltage Vout.

10. Plot the output waveforms for the below two circuits.

11. Consider the below-given circuit, if Vout is known then which of the following options will be correct?

1. The bias currents will be unknown
2. The offset current will be known
3. The bias and offset currents will be known.
4. None of the above

12. Design a circuit to implement 3V1-V2 using a single operational amplifier where V1 and V2 are the input signal voltages.

13. Consider the following Opamp circuit and find the voltage Vout.

14. Refer the following Opamp circuit, If voltage V1 = 5sinwt and saturation voltage Vsat = +/- 15V, Then plot the curve V2 superimposed on V1.

15. Consider the following circuit. If the switch in the circuit is closed for 30 seconds and then it is opened. The output voltage which was initially at 0V becomes -5.4V when the switch is opened. What is the voltage value of the input signal Vi?

16. In a system, three similar amplifiers are connected in the cascade configuration. These amplifiers have 3dB bandwidth of 100KHz each. What is the approximate overall bandwidth of the system? [Given that 10^0.1 = 1.2589].
17. If there are three similar voltage-controlled-voltage-amplifiers are connected in a cascade configuration. Each of the amplifiers has a voltage gain of 50, and an input impedance Zin of 1 kOhm. And the output impedance of each amplifier is 0.25 kOhm. Calculate the open-circuit voltage gain Aoc of the overall circuit.

18. For the given opamp circuit calculate the upper threshold point UTP and lower threshold point LTP. Given saturation voltage Vsat = +/- 10V.

19. By considering the below circuit plot the output waveform Vout.

20. An Opamp having a slew rate of 36.1 V/µs and an input square wave signal with 8Vp-p and frequency of 3.6 MHz to the voltage follower circuit. Calculate the output waveform of the circuit?
21. The MOS devices have a low turnoff time and they can be operated at high frequencies compared to BJT transistors because of
1. MOS devices have high input impedance.
2. MOS devices are voltage-controlled devices.
3. In MOSFET the storage time of minority carriers is absent.
4. MOS devices have a positive temperature coefficient.

22. Plot the output waveforms for the RC circuits shown below.

23. Assume the diodes are ideal and find the voltage Vout and current I for the given circuits.

24. Consider the below circuit and draw the output voltage waveform for the input given.

25. Assume Vthn = 1V and Vthp = -1V. Draw the output voltage waveform for the circuit shown below.

26. What is the type of the ADC (Analog to Digital converter) circuit, that is of 12-bit and operating with a clock period T of 1µsec?. The total conversion time of the ADC is given as 12 µsec.