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Question 1. Which parameter most directly determines the reverse recovery time of a power diode? A) Forward voltage drop B) Junction capacitance C) Stored charge during forward conduction D) Thermal resistance Answer: C Explanation: Reverse recovery time is dominated by the amount of minority carrier charge stored in the diode during forward conduction; this charge must be removed when the diode switches off. Question 2. In a MOSFET, the Safe Operating Area (SOA) is primarily limited by: A) Gate threshold voltage B) Drain-source on-resistance (RDS(on)) C) Maximum allowable power dissipation and transient thermal response D) Body diode forward voltage Answer: C Explanation: The SOA defines the combination of voltage and current that a MOSFET can handle without exceeding its thermal limits; it is governed by power dissipation and how quickly the device can dissipate heat. Question 3. An IGBT combines the advantages of a MOSFET and a BJT because: A) It has a high input impedance like a MOSFET and low on-state voltage drop like a BJT B) It uses a bipolar gate structure C) It operates only in the linear region D) It has a built-in Zener diode
Answer: A Explanation: The MOSFET-driven gate provides high input impedance, while the bipolar conduction channel gives the IGBT low saturation voltage similar to a BJT. Question 4. The two-transistor analogy for an SCR consists of: A) Two MOSFETs in parallel B) A PNPN thyristor modelled as a forward-biased transistor and a reverse-biased transistor C) Two identical diodes in series D) A Darlington pair Answer: B Explanation: The SCR can be represented by a forward-biased NPN transistor and a reverse-biased PNP transistor whose interaction explains latching behavior. Question 5. Which triggering method provides the fastest turn-on time for an SCR? A) Gate-pulse triggering B) Thermal triggering C) Light-triggered (photothyristor) D) Current-triggered (forward-bias) Answer: A Explanation: A short, high-current gate pulse injects carriers directly into the SCR’s junction, causing rapid turn-on compared to other methods. Question 6. A DIAC is most commonly used for: A) DC voltage regulation B) Triggering the gate of a TRIAC at a specific voltage C) Power factor correction
B) Increased output swing C) Output error proportional to gain D) Lower input bias current Answer: C Explanation: Input offset voltage appears at the output multiplied by the closed-loop gain, causing a systematic error in the amplified signal. Question 10. Common-mode rejection ratio (CMRR) is expressed in: A) Volts per ampere B) Decibels (dB) C) Hertz (Hz) D) Ohms (Ω) Answer: B Explanation: CMRR quantifies how well an op-amp rejects common-mode signals relative to differential signals, and it is typically expressed in dB. Question 11. Which of the following limits the slew rate of an op-amp? A) Input bias current B) Output stage current-charging capability of internal compensation capacitor C) Power supply ripple D) Input offset current Answer: B Explanation: The slew rate is determined by the maximum current the output stage can deliver to charge the internal compensation capacitor, limiting how fast the output can change.
Question 12. For a unity-gain stable op-amp, the gain-bandwidth product (GBW) is equal to: A) The closed-loop bandwidth at gain = 1 B) The open-loop gain at DC C) The product of open-loop gain and phase margin D) The input resistance Answer: A Explanation: At unity gain, the closed-loop bandwidth equals the GBW because the gain is 1, so the product of gain and bandwidth remains constant. Question 13. In a precision full-wave rectifier using an op-amp, the diode is placed: A) In the feedback path to force the op-amp to conduct during both half-cycles B) At the input stage only C) In series with the output load D) Across the power supply Answer: A Explanation: The diode in the feedback loop allows the op-amp to maintain linear operation during both positive and negative input excursions, achieving precise rectification. Question 14. A logarithmic amplifier using a transdiode configuration relies on which semiconductor property? A) Linear I-V characteristic of a resistor B) Exponential I-V relationship of a diode or BJT base-emitter junction C) Saturation voltage of a MOSFET D) Reverse breakdown of a Zener diode
C) Remains unchanged D) Becomes infinite Answer: B Explanation: Voltage-series feedback feeds back a voltage sample in series with the input, effectively raising the input impedance. Question 18. Feedback that reduces output impedance of an amplifier is: A) Voltage-series B) Voltage-shunt C) Current-series D) Current-shunt Answer: D Explanation: Current-shunt (shunt-feedback) feeds back a current sample in parallel with the output, lowering the output impedance. Question 19. The Barkhausen criterion for sustained oscillation requires: A) Loop gain > 1 and total phase shift = 0° (or 360°) B) Loop gain = 0 and phase shift = 90° C) Loop gain < 1 and phase shift = 180° D) Loop gain = 1 and total phase shift = 180° Answer: A Explanation: For steady oscillations, the product of gains around the loop must be unity (or greater) and the total phase shift must be an integer multiple of 360°. Question 20. In a phase-shift RC oscillator, the frequency of oscillation is primarily set by:
A) The inductance of the coil B) The RC network time constants C) The supply voltage D) The op-amp slew rate Answer: B Explanation: The three-stage RC network provides 180° phase shift; the oscillation frequency is determined by the RC product of each stage. Question 21. The frequency of a Wien-bridge oscillator is given by f = 1/(2πRC). Which component tolerance will most affect frequency stability? A) Op-amp input bias current B) Resistor tolerance C) Power-supply ripple D) Capacitor ESR Answer: B Explanation: Since frequency depends directly on the product RC, any variation in resistor value (or capacitor) will shift the frequency; resistor tolerance is often the dominant factor. Question 22. In a Hartley LC oscillator, the feedback ratio is set by: A) The ratio of the two inductors (or one inductor with a tapped coil) B) The capacitance of the tank circuit C) The supply voltage magnitude D) The load resistance Answer: A Explanation: The Hartley oscillator uses a tapped inductor (or two inductors) to provide the required feedback voltage division.
Explanation: Crystals provide a very high Q factor, resulting in excellent frequency stability and low phase noise compared with LC tanks. Question 26. An astable multivibrator using a 555 timer produces: A) A single pulse of fixed width B) A continuous square wave with frequency determined by external resistors and capacitor C) A bistable latch D) A PWM signal only Answer: B Explanation: In astable mode, the 555 charges and discharges a timing capacitor through two resistors, generating a free-running square wave. Question 27. A monostable 555 configuration is triggered by: A) A rising edge on the trigger pin (pin 2) B) A falling edge on the reset pin (pin 4) C) Continuous high on the threshold pin (pin 6) D) A low-level on the discharge pin (pin 7) Answer: A Explanation: A low-level pulse on the trigger pin initiates a single timing cycle, after which the output returns to its idle state. Question 28. The hysteresis of a Schmitt trigger is primarily introduced by: A) Positive feedback through a resistor network B) Negative feedback through a capacitor C) The supply voltage ripple D) The op-amp input offset voltage
Answer: A Explanation: Positive feedback creates two distinct threshold voltages (upper and lower), giving the Schmitt trigger its characteristic hysteresis. Question 29. A Zener diode used as a shunt regulator maintains a constant voltage by: A) Conducting only when reverse-biased beyond the Zener voltage, thus clamping the voltage B) Acting as a forward-biased diode C) Varying its resistance linearly with current D) Providing a constant current source Answer: A Explanation: When the reverse voltage exceeds the Zener breakdown voltage, the diode conducts heavily, keeping the voltage across it near the Zener value. Question 30. In a series-pass linear regulator, the pass transistor: A) Is always a PNP device B) Drops the excess voltage and supplies a regulated output voltage C) Operates only in cutoff mode D) Provides current limiting by itself Answer: B Explanation: The series-pass transistor acts as a variable resistor, dropping the difference between input and output while maintaining regulation via a control loop. Question 31. The LM317 adjustable regulator sets its output voltage using: A) A fixed Zener reference only B) An external resistor divider between output and adjust pins
Question 34. Lithography in IC fabrication is used to: A) Implant dopants into the silicon wafer B) Define the geometric patterns of circuit features by transferring a mask onto a photoresist layer C) Remove metal layers D) Measure wafer thickness Answer: B Explanation: Lithography projects the mask pattern onto a photosensitive resist, allowing selective etching or doping of the underlying substrate. Question 35. Ion implantation differs from diffusion primarily because: A) It introduces dopants at room temperature with precise dose control and depth profiling B) It requires high-temperature annealing for activation C) It cannot be used for p-type dopants D) It creates only surface-level doping Answer: A Explanation: Ion implantation accelerates dopant ions into the wafer, allowing accurate control of concentration and depth without the high temperatures required for diffusion. Question 36. A monolithic IC is distinguished from a hybrid IC by: A) All active and passive components fabricated on a single semiconductor substrate B) Use of discrete components mounted on a substrate C) Higher power handling capability D) Being limited to digital logic only
Answer: A Explanation: Monolithic ICs integrate all devices on one silicon die, whereas hybrid ICs combine separate dies or discrete parts on a common package. Question 37. Which logic family typically offers the fastest switching speed but the highest power consumption? A) TTL B) CMOS C) ECL D) NMOS Answer: C Explanation: Emitter-Coupled Logic (ECL) uses constant-current differential amplifiers, giving very high speed at the cost of substantial power dissipation. Question 38. In CMOS technology, the parameter “fan-out” refers to: A) The number of inputs a gate can drive without exceeding its output current capability B) The number of transistors in a gate C) The propagation delay per gate D) The power-delay product Answer: A Explanation: Fan-out is the maximum number of identical inputs that a CMOS gate’s output can drive while maintaining specified voltage levels. Question 39. The propagation delay of a TTL gate is typically: A) 1–10 ns B) 100–200 ns C) 0.1–0.5 ns
Question 42. In a flash ADC, the number of comparators required for an N-bit conversion is: A) N B) 2ⁿ – 1 C) 2ⁿ D) √N Answer: B Explanation: A flash ADC uses a resistor ladder and a comparator for each possible code transition, requiring 2ⁿ – 1 comparators to resolve N bits simultaneously. Question 43. The successive-approximation register (SAR) ADC determines each bit by: A) Simultaneously comparing the input to all reference levels B) Iteratively testing the most significant bit first, then proceeding to less significant bits, using a binary search algorithm C) Integrating the input over a fixed time D) Using a delta-sigma modulator Answer: B Explanation: The SAR algorithm performs a binary search, setting each bit based on the comparison of the input voltage with a DAC output representing the tentative digital code. Question 44. In a dual-slope integrating ADC, the conversion time is proportional to: A) The input voltage magnitude B) The reference voltage only C) The clock frequency only D) The product of integration time and reference voltage
Answer: D Explanation: The first integration period is fixed; the de-integration time is proportional to the input voltage, and the total conversion time depends on both the reference voltage and clock frequency. Question 45. A single-tuned RF amplifier consists of: A) One resonant LC circuit at the input (or output) providing a narrow bandwidth centered at the resonant frequency B) Two cascaded tuned circuits for wider bandwidth C) A broadband resistive load D) A crystal filter Answer: A Explanation: A single-tuned amplifier uses a single resonant tank either at the input or output to provide gain only near its resonant frequency. Question 46. Thermal noise (Johnson-Nyquist noise) in a resistor is proportional to: A) The square root of the resistance and absolute temperature, and the square root of bandwidth B) The square of the voltage across the resistor C) The diode forward voltage D) The inductance of a coil Answer: A Explanation: Thermal noise voltage density is √(4 k T R Δf); it increases with resistance, temperature, and the square root of bandwidth. Question 47. Shot noise originates from: A) Random fluctuations of charge carriers crossing a potential barrier, such as a pn-junction diode, and is proportional to the average current
Question 50. A basic FM demodulator using a slope detector converts frequency variations into: A) Amplitude variations across a tuned RC network, which are then rectified B) Direct voltage proportional to instantaneous frequency C) Phase shifts only D) No output, as FM cannot be demodulated with passive components Answer: A Explanation: In a slope detector, the input FM signal passes through a band-pass filter with a linear amplitude-frequency response; frequency deviations become amplitude changes that are then detected. Question 51. In a phase-locked loop (PLL), the voltage-controlled oscillator (VCO) frequency is adjusted by: A) The phase detector output filtered by a loop filter, producing a control voltage B) Directly feeding the input frequency to the VCO C) Changing the supply voltage only D) Varying the load resistance Answer: A Explanation: The phase detector compares input and feedback phases; its output, after filtering, becomes the control voltage that tunes the VCO frequency. Question 52. A PLL used for frequency synthesis can generate a frequency that is: A) An integer multiple of the reference frequency (N × f_ref) when a frequency divider is placed in the feedback path B) Exactly the same as the reference frequency only C) Randomly varying with temperature D) Limited to below the reference frequency
Answer: A Explanation: By inserting a programmable divide-by-N counter in the feedback, the VCO locks to N times the reference, enabling precise frequency synthesis. Question 53. In a voltage-shunt feedback amplifier, the closed-loop gain is given by: A) A_OL / (1 + β A_OL) where β is the feedback factor derived from shunt sampling B) A_OL · (1 + β A_OL) C) 1 / β D) A_OL only Answer: A Explanation: The standard feedback formula applies; for shunt feedback β is the fraction of output voltage fed back to the input node. Question 54. The input bias current of an op-amp contributes to offset error most significantly when: A) The source resistance at the input is high B) The supply voltage is low C) The load resistance is high D) The op-amp is used in a voltage follower Answer: A Explanation: Input bias currents flow through source resistances, creating voltage drops that appear as additional offset at the input. Question 55. A Sallen-Key low-pass filter of second order uses: A) Two resistors and two capacitors with a unity-gain buffer (op-amp) B) An inductor and a capacitor only
