Linear integrated circuit Interview Questions & Answers

  1. Question 1. If Output Is Measured Between Two Collectors Of Transistors, Then The Differential Amplifier With Two Input Signal Is Said To Be Configured As?

    Answer :

    When two input signals are applied to base of transistor, it is said to be Dual Input. When both collectors are at same DC potential with respect to ground, then it is said to be Balance Output.

  2. Question 2. A Differential Amplifier Is Capable Of Amplifying?

    Answer :

    Direct connection between stages removes the lower cut off frequency imposed by coupling capacitor; therefore it can amplify both AC and DC signal.

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  4. Question 3. Which Is Not The Internal Circuit Of Operational Amplifier?

    Answer :

    Clamper is an external circuit connected at the output of Operational amplifier, which clamp the output to desire DC level.

  5. Question 4. The Purpose Of Level Shifter In Op-amp Internal Circuit Is To?

    Answer :

    The gain stages in Op-amp are direct coupled. So, level shifter is used for adjustment of DC level.

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  7. Question 5. How A Symmetrical Swing Is Obtained At The Output Of Op-amp?

    Answer :

    For example, consider a single voltage supply +15v. During positive half cycle the output will be +5v and -10v during negative half cycle.

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  9. Question 6. What Is The Purpose Of Differential Amplifier Stage In Internal Circuit Of Op-amp?

    Answer :

    Any undesired noise, common to both of the input terminal is suppressed by differential amplifier.

  10. Question 7. What Will Be The Emitter Current In A Differential Amplifier, Where Both The Transistor Are Biased And Matched? (assume Current To Be Iq)

    Answer :

    Due to symmetry of differential amplifier circuit, current IQ divides equally through both transistors.

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  12. Question 8. Change In Value Of Common Mode Input Signal In Differential Pair Amplifier Make?

    Answer :

    In differential amplifier due to symmetry, both transistors are biased and matched. Therefore, Voltage at each collector will be same.

  13. Question 9. How Are The Arbitrary Signal Represented, That Are Applied To The Input Of Transistor?

    Answer :

    In practical situation, arbitrary signal are signal are represented as Sum and Difference of common mode signal and differential mode signal.

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  15. Question 10. How The Differential Mode Gain Is Expressed Using ‘h’ Parameter For A Single Ended Output?

    Answer :

    Formula for differential mode gain using ‘h’ parameter model for a single ended output.

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  17. Question 11. To Increase The Value Of Cmrr, Which Circuit Is Used To Replace The Emitter Resistance Re In Differential Amplifier?

    Answer :

    Constant current bias offers extremely large resistor under AC condition and thus provide high CMRR value.

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  19. Question 12. What Is The Purpose Of Diode In Differential Amplifier With Constant Current Circuit?

    Answer :

    The base emitter voltage of transistor (VBE) in constant current circuit by 2.5mv/oc, thus diode also has same temperature. Hence two variations cancel each other and total current IQ become in depend of temperature.

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  21. Question 13. How To Improve Cmrr Value?

    Answer :

    For a large CMRR value, ACM should be small as possible.

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  23. Question 14. Define Total Current (iq) Equation In Differential Amplifier With Constant Current Bias Current?

    Answer :

    The equation for total current is obtained by applying Kirchhoff’s Voltage Law to constant current circuit in differential amplifier.

  24. Question 15. A Widlar Current Source Is Used?

    Answer :

    In the widlar current source Re is added to emitter lead of transistor, which consequently results in smaller output current value.

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  26. Question 16. Which Current Source Exhibits A Very High Output Resistance?

    Answer :

    The output resistance of Wilson current mirror is substantially greater than ≅(β× Output resistance)/2 than Simple or Widlar current source.

  27. Question 17. What Will Be The Overall Gain In Darlington Circuit, If The Individual Transistor Gain Is 200?

    Answer :

    Overall current gain, β= β1×β2 (Multiplication of current gain of individual transistor)

    ⇒ β=200×200=40000

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  29. Question 18. To Increase The Input Resistance In Differential Amplifier, Replace The Transistor By?

    Answer :

    Higher value of input resistance can be obtained by using Darlington pair in place of transistor.

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  31. Question 19. What Is The Drawback In Using Darlington Pair In Differential Amplifier?

    Answer :

    Due to cascaded stage, Darlington differential amplifier offers higher offset voltage which is two times larger than ordinary two transistor used in differential amplifier.

  32. Question 20. Determine The Amount Of Shift Happens In Level Shifter?

    Answer :

    Level shifter is basically a simple type emitter follower. Hence, level shifter also act as a buffer to isolate high gain stages from the output stage. Therefore, the amount of shift obtained is

    VO – Vi = -VBE = -0.7v.

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  34. Question 21. Why Active Load Is Used In Amplifier To Obtain Large Gain In Intermediate Stage Of Amplifier?

    Answer :

    To increase gain usually large collector resistance value as gain is proportional to load resistor. However, due to limitation of maximum value load resistor, active loads are used in amplifier to obtain large gain in intermediate stages of amplifier.