Electronic Devices and Circuits : Important interview Questions Part 4

1. What is 𝞹- model?

Ans. The hybrid 𝞹-model is a linearized two-port network approximation to the BJT using the small signal base-emitter voltage (V_be) and collector-emitter (v_ce) voltage as independent variables and the small signal base current (i_b) and collector current (i_c) as dependent variables. The model can be quite accurate for low frequency circuits.

2. What is differential Amplifier and its significance?

Ans. Amplifier which amplifies difference between two input signals is referred to as differential amplifier. It supresses the unwanted disturbance that might be amplifier with the desired signal.

3. What is CMRR and its significance?

Ans.

• CMRR of differential amplifier is the ability of the amplifier to reject common mode signals. High CMRR means amplifier is able to reject common mode signals better.
• It is ratio of A_d to A_cm. 

4. Why swamping resistors are used in differential amplifier and what are its effects.

Ans. In differential amplifier voltage gain

   and R_e temperature dependent. So to swamp out the effect of R_e i.e. for stable voltage gain. Swamping resistors R’_E in series with each emitter are used.

Swamping resistor reduce voltage gain, and increase input resistance and doesn’t affect R_out.

5. What is the advantage of using constant current bias circuit?

Ans. Constant current bias circuit supplies constant emitter current. It also provides very high source resistance since the ac equivalent of the dc current source is ideally an open circuit.

6. What is input offset voltage in OP-AMP?

Ans. Input offset voltage is the voltage that must be applied between the two input terminal of an OP-AMP to null the output.

7. What is input offset current in OP-AMP?

Ans. The algebric difference between the currents into the inverting and non-inverting terminals is referred to as input offset current I_io.

                                           I_io = |I_B1 – I_B2|

8. What is input bias current?

Ans. I_B is the average of the currents that flows into the inverting and non-investing input terminals of the OP-AMP,

9. What is differential input resistance (R_i) in OP-AMP?

Ans. R_i is the equivalent resistance that can be measured at either the inverting or non-inverting input terminal with the other terminal connected to ground.

10. What is input capacitance (C_i) in OP-AMP?

Ans. C_i is the equivalent capacitance that can be measured at either the inverting or non-inverting terminal with the other terminal connected to ground.

11. What is output offset voltage in OP-AMP?

Ans. Output voltage without any input applied is called output offset voltage i.e. output voltage caused by mismatching between two input terminal it is denoted by V_00.

12. What is offset voltage adjustment range in OP-AMP?

Ans. By varying the potentiometer, the V₀₀ can be reduced to zero volts. Thus the offset voltage adjustment range is the range through which input offset voltage can be adjusted by varying the 10-kΩ potentiometer.

13. What is supply voltage rejection ratio (SVRR)/power supply rejection ratio (PSRR)/ power supply sensitivity (PSS) in OP-AMP?

Ans. The change in an OP-AMPs input offset voltage V_i0 caused by variations in supply voltage is called SVRR,

      µV/V → Lower the value of SVRR in µV/V, the better the OP-AMP performance.

14. What is output resistance (R₀) in OP-AMP?

Ans. R₀ is the equivalent resistance that can be measured between the output terminal of the OP-AMP and ground. It is 75Ω for 741C OP-AMP?\

15. What is power consumption (P_c) in OP-AMP?

Ans. P_c is the amount of quiescent power (V_in = 0) that is consumed by the OP-AMP in order to operate properly.

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