EC-405 Analog Circuits - Jun 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain the concept of positive and negative feedback with suitable waveform? Discuss Barkhausen criterion.
   How to answer

   • Define positive feedback with in-phase feedback waveform
   • Define negative feedback with out-of-phase feedback waveform
   • State Barkhausen criterion magnitude and phase condition
   • Explain role in oscillators vs amplifiers
2. 7 Marks
   bCalculate the voltage gain of the following circuit:

   

   How to answer

   • Identify biasing topology from circuit R1, R2, RE
   • Calculate emitter / voltage gain formula
   • Substitute R1=10 kΩ, R2=10 kΩ, RE=5 kΩ, +Vcc=10V
   • Obtain voltage gain value
3. 7 Marks
   aWhat is an integrated circuit? Discuss the relative advantages and disadvantages of ICs over discrete assembly.
   How to answer

   • Define integrated circuit
   • List advantages over discrete assembly
   • List disadvantages/limitations
   • Conclude comparison
4. 7 Marks
   bWith a neat diagram, explain the action of Hartley's oscillators. A phase shift oscillator uses $8\text{ pF}$ capacitors. Find the value of Resistor (R) to produce a frequency of $600\text{ kHz}$.
   How to answer

   • Draw neat Hartley oscillator circuit with tapped inductor
   • Explain feedback action and Barkhausen condition
   • State frequency formula f=1/(2π√(Leq·C))
   • Calculate R for phase-shift oscillator with C=8pF, f=600kHz using f=1/(2πRC√6)
5. 7 Marks
   aDiscuss Input offset voltage, offset current, Input bias current, Output offset voltage.
   How to answer

   • Define input offset voltage
   • Define input offset current and input bias current
   • Define output offset voltage
   • Explain causes and effects
6. 7 Marks
   bExplain in brief Butterworth $2^{nd}$ order Low pass FILTER.
   How to answer

   • State Butterworth maximally flat response concept
   • Show 2nd order low-pass topology with op-amp
   • Give transfer function and cutoff frequency
   • Mention roll-off -40 dB/decade
7. 7 Marks
   aDiscuss the operation of Fixed and Adjustable Voltage Regulators.
   How to answer

   • Explain fixed regulator e.g. 78XX operation
   • Explain adjustable regulator e.g. LM317 operation
   • Show block/circuit diagrams
   • Compare regulation method
8. 7 Marks
   bDerive an expression for the common-mode voltage gian of a differential amplifier.
   How to answer

   • Define differential and common-mode inputs
   • Draw common-mode half-circuit analysis
   • Derive voltage gain expression Acm
   • State significance of CMRR
9. 7 Marks
   aDifferentiate Monostable, Bistable and Astable Multivibrator.
   How to answer

   • Define stable states concept
   • Distinguish monostable one stable state
   • Distinguish bistable two stable and astable zero stable
   • Give examples/applications
10. 7 Marks
    bExplain in brief Zero Crossing Detector.
    How to answer

    • Define zero crossing detector principle
    • Show op-amp comparator circuit with waveforms
    • Explain output switching at zero crossing
11. 7 Marks
    aFind the output voltage ($V_{out}$) for each of the following combinations:

    

    How to answer

    • Write summing amplifier formula Vout = -(Rf/R1·V1+Rf/R2·V2+Rf/R3·V3)
    • Substitute V1,V2,V3 for each row with R1=1kΩ,R2=2kΩ,R3=4kΩ,Rf=1kΩ
    • Compute ideal Vout and check saturation at ±20V
    • Give final Vout for three combinations
12. 7 Marks
    bDiscuss the operation of OP-AMP as integrator.
    How to answer

    • Show integrator circuit with R input and C feedback
    • Derive Vout = -1/RC ∫Vin dt
    • Explain frequency response and limitations
    • Give output waveform example
13. 7 Marks
    aDiscuss the Effect of variation in power supply voltage of an OP-AMP. Explain the importance of gain bandwidth product.
    How to answer

    • Explain effect of supply variation on saturation and bias
    • Define gain-bandwidth product GBP = Gain × BW
    • Explain constant GBP and frequency limitation
    • Mention stability importance
14. 7 Marks
    bDiscuss the application of OP-AMP as Voltage-shunt feedback amplifier.
    How to answer

    • Show voltage-shunt feedback topology
    • Derive gain with feedback and input resistance
    • Explain virtual ground operation
    • Mention applications
15. 14 Marks
    Write short note on :

    1. a)VCO
    2. b)Slew rate and its effect on OP-AMP
    3. c)Dual input balanced output DA
    How to answer

    • Define VCO and its voltage-frequency relation
    • Define slew rate formula and its effect on distortion/bandwidth
    • Explain dual input balanced output differential amplifier
    • Give circuit/diagram and applications for each