EX-305 Analog Electronics - Jun 2024 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
   aWhat is CMOS? Write its merits.
   How to answer

   • Definition of CMOS as Complementary MOS using NMOS and PMOS pair
   • Basic structure / working principle
   • Merits: low power, high noise immunity, high density, etc.
   • Applications
2. 7 Marks
   bDefine $\alpha$ and $\beta$ of a transistor and derive relationships between them.
   How to answer

   • Define alpha as CB current gain $I_C/I_E$
   • Define beta as CE current gain $I_C/I_B$
   • Relation $I_E = I_C + I_B$ derivation steps
   • Final formulas $\beta = \alpha/(1-\alpha)$ and $\alpha = \beta/(1+\beta)$
3. 7 Marks
   aDetermine the ripple factor of L type choke input filter comprising a $10H$ choke and $8\mu F$ capacitor used with FWR. Compare with simple $8\mu F$ capacitor input filter at a load current of $50\text{ mA}$? Assume DC voltage is $50V$.
   How to answer

   • Ripple factor formula for L-type choke input filter
   • Substitute $L=10H$, $C=8\mu F$ for FWR
   • Ripple factor formula for capacitor input filter with $I_{DC}=50mA$, $V_{DC}=50V$
   • Comparison conclusion
4. 7 Marks
   bContrast between CB, CE and CC configurations.
   How to answer

   • Configuration definitions CB, CE, CC
   • Comparison of input/output impedance, gain
   • Comparison of applications
   • Tabular summary
5. 7 Marks
   aDiscuss load line analysis.
   How to answer

   • Concept of load line and Q-point
   • DC load line construction
   • AC load line and significance
   • Diagram of load line on characteristics
6. 7 Marks
   bA self biased p-channel JFET has pinch-off voltage of $V_P=5V$ and $I_{DSS}=12mA$. The supply voltage is $12V$. Determine the values of $R_D$ and $R_S$ so that $I_D=5\text{ mA}$ and $V_{DS}=6V$.
   How to answer

   • JFET drain current equation $I_D = I_{DSS}(1-V_{GS}/V_P)^2$
   • Find $V_{GS}$ for $I_D=5mA$
   • Apply KVL for output loop with $V_{DS}=6V$, $V_{DD}=12V$
   • Solve for $R_D$ and $R_S$
7. 7 Marks
   aDiscuss about thermal runway and thermal stability.
   How to answer

   • Definition of thermal runaway mechanism
   • Effect of temperature on ICO and stability factor
   • Conditions for thermal stability
   • Biasing methods to prevent runaway
8. 7 Marks
   bExplain the working principle of FET.
   How to answer

   • Structure of FET (gate, source, drain, channel)
   • Formation of depletion region with VGS
   • Pinch-off and saturation operation
   • Control of drain current by gate voltage
9. 7 Marks
   aDiscuss clipper and how a double ended clipper with equal and unequal amplitude can be implemented explain with suitable example and diagram.
   How to answer

   • Definition and types of clipper
   • Double ended clipper with equal amplitude
   • Double ended clipper with unequal amplitude
   • Example circuit with diagram and waveforms
10. 7 Marks
    bExplain Darlington pair transistor circuit.
    How to answer

    • Darlington pair configuration using two transistors
    • Current gain multiplication principle
    • Circuit diagram and operation
    • Advantages / applications
11. 7 Marks
    aDiscuss Clamping theorem and design any biased positive clamper with neatly drawn waveforms.
    How to answer

    • Statement of clamping theorem
    • Biased positive clamper circuit design
    • Operation with capacitor charging
    • Neat input-output waveforms
12. 7 Marks
    bA differential amplifier has an output of $1V$ with a differential input of $10\text{ mV}$ and an output of $5\text{ mV}$ with a common mode input of $10\text{ mV}$. Find out CMRR in dB.
    How to answer

    • Differential gain $A_d = V_{od}/V_{id}$
    • Common mode gain $A_c = V_{oc}/V_{ic}$
    • CMRR $= A_d/A_c$ and in dB $20\log(CMRR)$
    • Substitute $1V/10mV$ and $5mV/10mV$ to get dB value
13. 7 Marks
    aExplain log amplifier and design logarithmic amplifier with input voltage $2V$ and current $50\text{ nA}$ at room temperature.
    How to answer

    • Principle of log amplifier using op-amp and diode/transistor
    • Transfer equation $V_o = -\eta V_T \ln(V_i/I_sR)$
    • Design steps for $V_i=2V$, $I=50nA$ at room temperature
    • Circuit diagram
14. 7 Marks
    bExplain Inverting zero crossing detector along with neat waveforms.
    How to answer

    • Inverting zero crossing detector circuit with op-amp
    • Reference voltage zero and working
    • Input sine and output square waveforms
    • Neat waveforms diagram
15. 14 Marks
    Write short note any two of the following:

    1. a)LC Oscillator
    2. b)DC Load Line
    3. c)LED
    4. d)BJT
    How to answer

    • Definition and principle of chosen two topics
    • Relevant circuit/diagram and working
    • Key formulas / characteristics
    • Applications