UPSC IES/ESE (Engineering Services) Electronics, Communication and Control Systems Syllabus

Electronics, Communication and Control Systems syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Electronics, Communication and Control Systems in UPSC IES/ESE (Engineering Services), not a summary of it.

1. 1

   Electronic Devices and Analog Circuits

   4 topics

   • Semiconductor physics, diodes and applications
   • BJT and FET biasing and amplifiers
   • Operational amplifiers and applications
     • Inverting and non-inverting configurations
     • Active filters and oscillators
   • Feedback amplifiers and power amplifiers
2. 2

   Digital Electronics and Microprocessors

   4 topics

   • Number systems and Boolean algebra
   • Combinational and sequential logic circuits
   • Counters, registers and memories
   • Microprocessor and microcontroller architecture
3. 3

   Signals and Systems

   4 topics

   • Continuous and discrete-time signals and systems
   • Fourier, Laplace and Z-transforms
   • Sampling theorem and aliasing
   • Linear time-invariant system analysis
4. 4

   Analog and Digital Communication

   4 topics

   • Amplitude and angle modulation
   • Noise in communication systems
   • Pulse and digital modulation
     • PCM, DPCM and delta modulation
     • ASK, FSK, PSK and QAM
   • Information theory and coding basics
5. 5

   Microwave, Antenna and Optical Communication

   4 topics

   • Transmission lines and waveguides
   • Microwave components and devices
   • Antenna fundamentals and radiation
   • Optical fibre communication and satellite systems
6. 6

   Control Systems

   4 topics

   • Modelling and transfer functions of systems
   • Time and frequency domain analysis
     • Transient and steady-state response
     • Bode, Nyquist and root locus
   • Stability analysis and compensators
   • State-space analysis and controllability

Electronics, Communication and Control Systems flashcards for UPSC IES/ESE (Engineering Services)

24 of 52 cards from the Electronics, Communication and Control Systems deck — real questions with worked answers.

1. In an intrinsic semiconductor, how is the intrinsic carrier concentration $n_i$ related to $N_C$, $N_V$, the band gap $E_g$, and temperature $T$?

   $$n_i = \sqrt{N_C N_V}\, e^{-E_g/(2kT)}$$ where $n_i$ doubles roughly every $\sim 10\,^\circ\text{C}$ for Si and increases strongly with $T$.

2. State the mass-action law for a doped semiconductor at thermal equilibrium.

   $n\,p = n_i^{2}$, independent of doping. For n-type $n \approx N_D$, $p = n_i^{2}/N_D$; for p-type $p \approx N_A$, $n = n_i^{2}/N_A$.

3. Write the Shockley diode equation relating diode current $I$ to voltage $V$.

   $$I = I_S\left(e^{V/(\eta V_T)} - 1\right)$$ where $I_S$ is reverse saturation current, $\eta$ the ideality factor, and $V_T = kT/q \approx 26\ \text{mV}$ at $300\ \text{K}$.

4. What is the typical cut-in (knee) voltage of Si and Ge diodes, and how does a Zener diode operate?

   Cut-in: Si $\approx 0.7\ \text{V}$, Ge $\approx 0.3\ \text{V}$. A Zener operates in reverse breakdown, maintaining a nearly constant voltage $V_Z$, used for voltage regulation.

5. For a full-wave rectifier with capacitor filter, give the approximate peak-to-peak ripple voltage and ripple frequency.

   $$V_{r(pp)} \approx \frac{I_{dc}}{2 f C}$$ for full-wave (factor $\tfrac{1}{fC}$ for half-wave). Ripple frequency $= 2f$ for full-wave, $f$ for half-wave.

6. In a BJT, define $\alpha$ and $\beta$ and give the relation between them.

   $\alpha = I_C/I_E$ (common-base gain), $\beta = I_C/I_B$ (common-emitter gain). $$\beta = \frac{\alpha}{1-\alpha}, \qquad \alpha = \frac{\beta}{1+\beta}$$ Also $I_E = I_C + I_B$.

7. Why is voltage-divider (self) bias preferred for BJT amplifiers, and what is its stability condition?

   It makes the Q-point nearly independent of $\beta$ and temperature. Stability requires $R_{Th} \ll (1+\beta)R_E$, achieved by a stiff divider so $V_B$ is fixed and $I_C \approx (V_B - V_{BE})/R_E$.

8. Give the small-signal transconductance $g_m$ of a BJT in terms of collector current.

   $$g_m = \frac{I_C}{V_T} \approx \frac{I_C}{26\ \text{mV}}$$ The input resistance $r_\pi = \beta/g_m$ and voltage gain (CE) $A_v = -g_m R_C$.

9. Write the drain current equation of an n-channel JFET in the saturation (pinch-off) region.

   $$I_D = I_{DSS}\left(1 - \frac{V_{GS}}{V_P}\right)^{2}$$ where $I_{DSS}$ is the drain current at $V_{GS}=0$ and $V_P$ is the pinch-off voltage.

10. Write the MOSFET drain current in saturation and the condition for saturation.

    $$I_D = \tfrac{1}{2}\mu_n C_{ox}\frac{W}{L}(V_{GS}-V_{th})^{2}$$ Saturation requires $V_{DS} \geq V_{GS} - V_{th}$ (i.e. $V_{GS} > V_{th}$ and channel pinched off).

11. List the ideal op-amp assumptions (virtual short / virtual ground).

    Infinite open-loop gain, infinite input impedance ($I_+ = I_- = 0$), zero output impedance, infinite bandwidth. With negative feedback $V_+ = V_-$ (virtual short).

12. Derive the closed-loop gain of an inverting op-amp amplifier.

    With virtual ground at the inverting input: $$A_v = -\frac{R_f}{R_1}$$ Input impedance $= R_1$; output is $180^\circ$ out of phase with input.

13. Give the closed-loop gain of a non-inverting op-amp amplifier and its input impedance.

    $$A_v = 1 + \frac{R_f}{R_1}$$ Input impedance is ideally infinite. A voltage follower is the special case $R_f = 0$, $R_1 = \infty$, giving $A_v = 1$.

14. For an ideal op-amp summing (inverting) amplifier with inputs $V_1, V_2, V_3$ through $R_1, R_2, R_3$ and feedback $R_f$, give $V_o$.

    $$V_o = -\left(\frac{R_f}{R_1}V_1 + \frac{R_f}{R_2}V_2 + \frac{R_f}{R_3}V_3\right)$$ If all input resistors equal $R$: $V_o = -\frac{R_f}{R}(V_1+V_2+V_3)$.

15. Give the output of an ideal op-amp integrator and differentiator.

    Integrator: $$V_o = -\frac{1}{RC}\int V_{in}\,dt$$ Differentiator: $$V_o = -RC\frac{dV_{in}}{dt}$$

16. Define slew rate and gain-bandwidth product of an op-amp.

    Slew rate $SR = \left.\frac{dV_o}{dt}\right|_{max}$ (V/$\mu$s), limits large-signal speed. Gain-bandwidth product $GBW = A_v \times f$ is constant for a single-pole op-amp; unity-gain bandwidth $f_T = A_{ol} f_{3dB}$.

17. Classify active filters by response and give the order of roll-off per pole.

    Types: low-pass, high-pass, band-pass, band-stop, all-pass. Each pole gives $-20\ \text{dB/decade}$ ($-6\ \text{dB/octave}$); an $n$-th order filter rolls off at $-20n\ \text{dB/decade}$.

18. State the Barkhausen criterion for sustained oscillation.

    Loop gain magnitude $|A\beta| = 1$ and total phase shift around the loop $= 0^\circ$ (or $360^\circ$). To start, $|A\beta| > 1$ initially.

19. Give the oscillation frequency of an RC phase-shift oscillator and a Wien-bridge oscillator.

    Phase-shift (3 RC sections): $$f = \frac{1}{2\pi RC\sqrt{6}}$$ Wien-bridge: $$f = \frac{1}{2\pi RC}$$ with required gain $\geq 3$ (Wien) and $\geq 29$ (phase-shift).

20. List the four feedback topologies and the parameter each stabilizes.

    Voltage-series (stabilizes voltage gain, $\uparrow R_i$, $\downarrow R_o$); current-series (transconductance); voltage-shunt (transresistance); current-shunt (current gain). Series feedback raises input R, shunt lowers it.

21. How do negative feedback with gain $A$ and feedback factor $\beta$ affect gain and bandwidth?

    Closed-loop gain $$A_f = \frac{A}{1+A\beta}$$ Bandwidth increases by factor $(1+A\beta)$; gain-bandwidth product stays constant. Distortion and gain sensitivity reduce by $(1+A\beta)$.

22. Compare Class A, B, AB, and C power amplifiers by conduction angle and max efficiency.

    Class A: $360^\circ$, $\eta_{max}=25\%$ (50% transformer-coupled). Class B: $180^\circ$, $\eta_{max}=78.5\%$. Class AB: slightly $>180^\circ$ (removes crossover distortion). Class C: $<180^\circ$, $\eta > 78.5\%$ (tuned RF).

23. Convert decimal $45$ to binary, octal and hexadecimal.

    $45_{10} = 101101_2 = 55_8 = 2D_{16}$.

24. State De Morgan's theorems in Boolean algebra.

    $$\overline{A+B} = \bar{A}\cdot\bar{B}, \qquad \overline{A\cdot B} = \bar{A}+\bar{B}$$ Generalized: complement the whole expression, complement each variable, and swap AND $\leftrightarrow$ OR.

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