GATE Biomedical Engineering Analog and Digital Electronics Syllabus

Analog and Digital Electronics syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Analog and Digital Electronics in GATE Biomedical Engineering, not a summary of it.

1. 1

   Basic characteristics and applications of diode, BJT and MOSFET

   3 topics

   • Diode
   • BJT (Bipolar Junction Transistor)
   • MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)
2. 2

   Characteristics and applications of operational amplifiers

   9 topics

   • Difference Amplifier
   • Adder
   • Subtractor
   • Integrator
   • Differentiator
   • Instrumentation Amplifier
   • Buffer
   • Filters
   • Waveform Generators
3. 3

   Number systems, Boolean algebra

   2 topics

   • Number Systems
   • Boolean Algebra
4. 4

   Combinational logic circuits

   6 topics

   • Arithmetic Circuits
   • Comparators
   • Schmitt Trigger
   • Encoder/Decoder
   • MUX/DEMUX
   • Multi-vibrators
5. 5

   Sequential circuits

   4 topics

   • Latches and Flip Flops
   • State Diagrams
   • Shift Registers
   • Counters
6. 6

   Principles of ADC and DAC

   2 topics

   • ADC (Analog-to-Digital Converter)
   • DAC (Digital-to-Analog Converter)
7. 7

   Microprocessor- architecture, interfacing memory and input-output devices

   3 topics

   • Microprocessor Architecture
   • Memory Interfacing
   • Input-Output Devices Interfacing

Analog and Digital Electronics flashcards for GATE Biomedical Engineering

24 of 51 cards from the Analog and Digital Electronics deck — real questions with worked answers.

1. What is a semiconductor diode and what is its fundamental property?

   A diode is a two-terminal PN-junction device that conducts current in one direction (forward bias) and blocks it in the other (reverse bias). It acts essentially as a one-way switch for current.

2. State the Shockley diode equation for current through a PN-junction diode.

   $$I = I_{S}\left(e^{\frac{V}{nV_{T}}} - 1\right)$$ where $I_{S}$ is the reverse saturation current, $n$ is the ideality factor, and $V_{T}$ is the thermal voltage.

3. What is the value of the thermal voltage $V_{T}$ at room temperature (300 K)?

   $$V_{T} = \frac{kT}{q} \approx 25.85\ \text{mV} \approx 26\ \text{mV}$$ where $k$ is Boltzmann's constant, $T$ the absolute temperature, and $q$ the electron charge.

4. What are the typical forward voltage drops (cut-in voltages) for silicon and germanium diodes?

   Silicon diode: about $0.7\ \text{V}$. Germanium diode: about $0.3\ \text{V}$.

5. How does a Zener diode operate and what is it used for?

   A Zener diode is operated in reverse breakdown, where it maintains a nearly constant voltage $V_{Z}$ across it despite current changes. It is used for voltage regulation and reference.

6. What is the difference between a half-wave and a full-wave rectifier in terms of output and ripple?

   A half-wave rectifier conducts on one half-cycle, giving $V_{dc} = \frac{V_{m}}{\pi}$ and ripple factor $1.21$. A full-wave rectifier uses both half-cycles, giving $V_{dc} = \frac{2V_{m}}{\pi}$ and ripple factor $0.48$.

7. What are the three regions of operation of a BJT?

   Cutoff (both junctions reverse biased, transistor OFF), Active (emitter-base forward, collector-base reverse — used for amplification), and Saturation (both junctions forward biased, transistor fully ON).

8. Define the BJT common-emitter current gain $\beta$ and its relation to $\alpha$.

   $$\beta = \frac{I_{C}}{I_{B}}, \qquad \alpha = \frac{I_{C}}{I_{E}}, \qquad \beta = \frac{\alpha}{1-\alpha}, \qquad \alpha = \frac{\beta}{\beta+1}$$

9. Write the fundamental current relationship between the three BJT terminal currents.

   $$I_{E} = I_{C} + I_{B}$$ The emitter current equals the sum of collector and base currents.

10. In the active region, how is the BJT collector current related to base-emitter voltage?

    $$I_{C} = I_{S}\,e^{\frac{V_{BE}}{V_{T}}}$$ The collector current depends exponentially on $V_{BE}$.

11. What is the difference between a MOSFET and a BJT in terms of control and carriers?

    A BJT is a current-controlled, bipolar device (uses both electrons and holes). A MOSFET is a voltage-controlled, unipolar device controlled by gate voltage, with very high input impedance.

12. State the MOSFET drain current equation in the saturation region.

    $$I_{D} = \frac{1}{2}\mu_{n}C_{ox}\frac{W}{L}\left(V_{GS}-V_{th}\right)^{2}$$ for $V_{GS} > V_{th}$ and $V_{DS} \geq V_{GS}-V_{th}$.

13. What is the condition for a MOSFET to operate in the triode (ohmic) region versus saturation?

    Triode/ohmic: $V_{DS} < V_{GS}-V_{th}$. Saturation: $V_{DS} \geq V_{GS}-V_{th}$. Cutoff: $V_{GS} < V_{th}$.

14. Distinguish enhancement-mode and depletion-mode MOSFETs.

    An enhancement-mode MOSFET is normally OFF and requires $V_{GS}$ beyond $V_{th}$ to form a channel. A depletion-mode MOSFET is normally ON (channel exists at $V_{GS}=0$) and the gate voltage depletes the channel.

15. What does a difference (differential) amplifier do, and what is the ideal op-amp output formula?

    It amplifies the difference between two input signals. For an ideal op-amp difference amplifier with matched resistors: $$V_{out} = \frac{R_{f}}{R_{1}}\left(V_{2}-V_{1}\right)$$

16. Define the Common-Mode Rejection Ratio (CMRR) of a difference amplifier.

    $$\text{CMRR} = \frac{A_{d}}{A_{cm}}, \qquad \text{CMRR (dB)} = 20\log_{10}\left|\frac{A_{d}}{A_{cm}}\right|$$ where $A_{d}$ is differential gain and $A_{cm}$ is common-mode gain. Higher CMRR is better.

17. Give the output expression for an inverting op-amp summing amplifier (adder).

    $$V_{out} = -R_{f}\left(\frac{V_{1}}{R_{1}}+\frac{V_{2}}{R_{2}}+\frac{V_{3}}{R_{3}}\right)$$ With all input resistors equal to $R$: $V_{out} = -\frac{R_{f}}{R}(V_{1}+V_{2}+V_{3})$.

18. What is the output of an op-amp subtractor with all four resistors equal?

    $$V_{out} = V_{2}-V_{1}$$ It produces the difference of the two inputs with unity gain.

19. State the output of an ideal op-amp integrator.

    $$V_{out} = -\frac{1}{RC}\int V_{in}\,dt$$ The output is proportional to the time integral of the input; $R$ is the input resistor and $C$ the feedback capacitor.

20. State the output of an ideal op-amp differentiator.

    $$V_{out} = -RC\,\frac{dV_{in}}{dt}$$ The output is proportional to the rate of change of the input; $C$ is the input capacitor and $R$ the feedback resistor.

21. What is an instrumentation amplifier and why is it preferred for biomedical signals?

    It is a precision difference amplifier (typically three op-amps) with very high input impedance, high CMRR, low noise, and an adjustable gain set by one resistor. These traits make it ideal for amplifying small differential bio-signals (ECG, EEG) in noisy environments.

22. Give the gain equation for the classic three-op-amp instrumentation amplifier.

    $$\frac{V_{out}}{V_{2}-V_{1}} = \left(1+\frac{2R}{R_{gain}}\right)\frac{R_{3}}{R_{2}}$$ where $R_{gain}$ is the single external gain-setting resistor.

23. What is a voltage buffer (voltage follower) and what is its gain?

    A buffer is a unity-gain amplifier ($V_{out}=V_{in}$, gain $=1$) with very high input impedance and very low output impedance. It isolates stages and prevents loading.

24. Why is impedance matching important and how does a buffer help?

    A buffer's high input impedance draws negligible current from the source, and its low output impedance can drive a load without signal drop. This prevents the load from affecting the previous stage (loading effect).

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