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DRDO MCQs

Practice DRDO-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 202
Analog ElectronicsTransistor Amplifiers

In a BJT amplifier operating in the active region, the base-emitter and base-collector junctions are respectively?

  • AForward biased
  • BReverse biased
  • CBoth forward biased
  • DBoth reverse biased
Report an error
Correct Answer: A. Forward biased
Explanation: For normal amplification the base-emitter junction is forward biased and the base-collector junction is reverse biased.
Reference: Standard analog electronics: transistor amplifiers
Question 205
Analog ElectronicsTransistor Amplifiers

A common-collector amplifier is particularly useful as a?

  • AHigh-voltage-gain stage
  • BBuffer and impedance-matching stage
  • CRectifier
  • DHigh-frequency oscillator only
Report an error
Correct Answer: B. Buffer and impedance-matching stage
Explanation: The emitter follower has high input resistance, low output resistance and voltage gain near unity.
Reference: Standard analog electronics: transistor amplifiers
Question 208
Analog ElectronicsBiasing & Stability

The Q-point of a transistor amplifier represents its?

  • AAC cutoff frequency
  • BQuiescent DC operating point
  • CMaximum power gain
  • DOscillation frequency
Report an error
Correct Answer: B. Quiescent DC operating point
Explanation: The Q-point specifies the steady DC voltage and current conditions with no input signal.
Reference: Standard analog electronics: biasing & stability
Question 209
Analog ElectronicsBiasing & Stability

For approximately symmetrical maximum undistorted swing in a simple class-A amplifier, the Q-point is usually placed near?

  • ACutoff
  • BSaturation
  • CMiddle of the DC load line
  • DBreakdown
Report an error
Correct Answer: C. Middle of the DC load line
Explanation: Biasing near the middle of the load line permits roughly equal signal excursions toward cutoff and saturation.
Reference: Standard analog electronics: biasing & stability
Question 210
Analog ElectronicsFeedback Amplifiers

Negative feedback generally makes an amplifier’s closed-loop gain?

  • AMore stable against parameter variations
  • BInfinitely large
  • CMore sensitive to transistor beta
  • DAlways zero
Report an error
Correct Answer: A. More stable against parameter variations
Explanation: Negative feedback sacrifices some gain but improves gain stability against device and circuit variations.
Reference: Standard analog electronics: feedback amplifiers
Question 211
Analog ElectronicsFeedback Amplifiers

Negative feedback generally has what effect on amplifier bandwidth?

  • AUsually decreases it to zero
  • BUsually increases it
  • CNever affects it
  • DMakes frequency negative
Report an error
Correct Answer: B. Usually increases it
Explanation: A common benefit of negative feedback is wider useful bandwidth while closed-loop gain is reduced.
Reference: Standard analog electronics: feedback amplifiers
Question 213
Analog ElectronicsOscillators

For sustained oscillation, the Barkhausen phase condition requires the total loop phase shift to be?

  • A90 degrees
  • B180 degrees only
  • C0 degrees or an integer multiple of 360 degrees
  • D45 degrees
Report an error
Correct Answer: C. 0 degrees or an integer multiple of 360 degrees
Explanation: Regenerative feedback requires a net loop phase of 0 degrees modulo 360 degrees at the oscillation frequency.
Reference: Standard analog electronics: oscillators
Question 214
Analog ElectronicsOscillators

A Wien-bridge oscillator is commonly used to generate?

  • ASinusoidal waveforms
  • BDC only
  • COnly sawtooth waves
  • DRandom noise only
Report an error
Correct Answer: A. Sinusoidal waveforms
Explanation: The Wien-bridge oscillator is widely used for low-distortion sinusoidal signal generation.
Reference: Standard analog electronics: oscillators
Question 220
Analog ElectronicsDifferential Amplifiers

CMRR is the ratio of?

  • ACommon-mode gain to differential gain
  • BDifferential gain to common-mode gain
  • COutput resistance to input resistance
  • DBandwidth to slew rate
Report an error
Correct Answer: B. Differential gain to common-mode gain
Explanation: CMRR = Ad/Acm and indicates rejection of signals common to both inputs.
Reference: Standard analog electronics: differential amplifiers
Question 221
Analog ElectronicsDifferential Amplifiers

A differential amplifier ideally amplifies?

  • AThe average of its inputs
  • BThe difference between its input voltages
  • COnly the supply voltage
  • DOnly common-mode signals
Report an error
Correct Answer: B. The difference between its input voltages
Explanation: A differential amplifier responds to the difference between its two input voltages.
Reference: Standard analog electronics: differential amplifiers
Question 222
Analog ElectronicsOperational Amplifiers

The slew rate of an op-amp is commonly expressed in?

  • AOhms
  • BVolts per microsecond
  • CAmperes per volt
  • DHertz per ohm
Report an error
Correct Answer: B. Volts per microsecond
Explanation: Slew rate is the maximum rate of change of output voltage, commonly specified in V per microsecond.
Reference: Standard analog electronics: operational amplifiers
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Question 226
Analog ElectronicsFrequency Response

The lower cutoff frequency of an RC-coupled amplifier is mainly influenced by?

  • ACoupling and bypass capacitors
  • BTransistor breakdown voltage only
  • CPower-supply frequency only
  • DCollector color code
Report an error
Correct Answer: A. Coupling and bypass capacitors
Explanation: At low frequencies, coupling and emitter-bypass capacitor reactances become significant and reduce gain.
Reference: Standard analog electronics: frequency response
Question 227
Analog ElectronicsFrequency Response

At high frequencies, the gain of a transistor amplifier generally falls mainly because of?

  • AJunction and stray capacitances
  • BCoupling capacitors becoming open circuits only
  • CDC bias becoming exactly zero
  • DLoad resistance becoming infinite
Report an error
Correct Answer: A. Junction and stray capacitances
Explanation: Internal junction capacitances, wiring capacitance and related high-frequency effects reduce amplifier gain.
Reference: Standard analog electronics: frequency response
Question 228
Analog ElectronicsFrequency Response

The Miller effect in an inverting voltage amplifier effectively makes a feedback capacitance between input and output appear at the input as?

  • AA reduced capacitance only
  • BAn increased effective capacitance
  • CZero capacitance
  • DA pure inductance
Report an error
Correct Answer: B. An increased effective capacitance
Explanation: Because the output is amplified and inverted, a capacitance bridging input and output can appear as a much larger effective input capacitance.
Reference: Standard analog electronics: frequency response
Question 236
Analog ElectronicsFeedback Amplifiers

An unbypassed emitter resistor in a common-emitter amplifier primarily introduces?

  • APositive feedback
  • BEmitter degeneration or negative feedback
  • COscillation at all frequencies
  • DAvalanche breakdown
Report an error
Correct Answer: B. Emitter degeneration or negative feedback
Explanation: The emitter resistor develops degenerative negative feedback, improving stability and linearity while reducing gain.
Reference: Standard analog electronics: feedback amplifiers
Question 242
Analog ElectronicsFeedback Amplifiers

In voltage-series negative feedback, the output resistance generally?

  • AIncreases
  • BDecreases
  • CBecomes infinite
  • DAlways equals input resistance
Report an error
Correct Answer: B. Decreases
Explanation: Voltage sampling with negative feedback generally lowers the closed-loop output resistance.
Reference: Standard analog electronics: feedback amplifiers
Question 244
Analog ElectronicsFeedback Amplifiers

An amplifier has A beta = 99. By what factor is its gain sensitivity to amplifier-parameter changes reduced compared with no feedback?

  • AApproximately 10
  • BApproximately 50
  • CApproximately 100
  • DApproximately 9900
Report an error
Correct Answer: C. Approximately 100
Explanation: The desensitivity factor is 1 + A beta = 100, so fractional gain variation is reduced by approximately a factor of 100.
Reference: Standard analog electronics: feedback amplifiers
Question 245
Analog ElectronicsOscillators

For a three-section RC phase-shift oscillator using identical RC sections in the usual idealized analysis, the amplifier must provide a gain magnitude of at least approximately?

  • A1
  • B3
  • C29
  • D100
Report an error
Correct Answer: C. 29
Explanation: The three-section RC network attenuates the signal; the standard idealized condition requires amplifier gain magnitude of at least about 29.
Reference: Standard analog electronics: oscillators
Question 248
Analog ElectronicsOscillators

In a Hartley oscillator, the frequency-selective tank circuit primarily uses?

  • ATwo capacitors and one resistor
  • BTwo inductive sections and a capacitor
  • COnly three resistors
  • DA crystal with no reactive components
Report an error
Correct Answer: B. Two inductive sections and a capacitor
Explanation: A Hartley oscillator uses a tapped inductor or two inductive sections with a capacitor to form its resonant tank.
Reference: Standard analog electronics: oscillators
Question 249
Analog ElectronicsOscillators

In a Colpitts oscillator, the feedback network characteristically uses?

  • AA capacitive divider
  • BAn inductive divider only
  • CA resistive bridge only
  • DA transformer rectifier
Report an error
Correct Answer: A. A capacitive divider
Explanation: A Colpitts oscillator uses two capacitors forming a capacitive divider together with an inductor.
Reference: Standard analog electronics: oscillators
Question 250
Analog ElectronicsOscillators

A crystal oscillator is preferred when the main requirement is?

  • AVery poor frequency stability
  • BHigh frequency stability
  • CLarge DC voltage regulation
  • DLow input resistance
Report an error
Correct Answer: B. High frequency stability
Explanation: Quartz crystals have very high Q and stable resonant characteristics, giving excellent oscillator frequency stability.
Reference: Standard analog electronics: oscillators
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Question 251
Analog ElectronicsDifferential Amplifiers

In an ideal BJT differential amplifier with perfectly matched transistors and equal collector resistors, applying the same signal to both inputs ideally produces a differential output of?

  • AZero
  • BEqual to twice the input
  • CInfinite
  • DEqual to the supply voltage
Report an error
Correct Answer: A. Zero
Explanation: An ideal differential amplifier rejects a signal common to both inputs, so the differential output due to a pure common-mode signal is zero.
Reference: Standard analog electronics: differential amplifiers
Question 254
Analog ElectronicsDifferential Amplifiers

The principal purpose of a constant-current source in the tail of a BJT differential pair is to?

  • AImprove bias stability and common-mode rejection
  • BMake both transistors permanently saturated
  • CReduce input resistance to zero
  • DRectify the input signal
Report an error
Correct Answer: A. Improve bias stability and common-mode rejection
Explanation: A high-resistance tail current source keeps the total emitter current nearly constant, improving differential operation and common-mode rejection.
Reference: Standard analog electronics: differential amplifiers
Question 255
Analog ElectronicsCurrent Mirrors

A basic two-transistor BJT current mirror is designed primarily to?

  • AGenerate an approximately replicated current
  • BGenerate a sine wave
  • CProvide voltage gain of exactly 100
  • DConvert AC directly to RF
Report an error
Correct Answer: A. Generate an approximately replicated current
Explanation: Matched transistors with equal base-emitter voltages can be arranged so an output collector current approximately mirrors a reference current.
Reference: Standard analog electronics: current mirrors
Question 257
Analog ElectronicsTransistor Amplifiers

The Early effect in a BJT causes collector current in the active region to?

  • ABe completely independent of VCE
  • BIncrease somewhat as VCE increases at fixed base drive
  • CBecome exactly zero
  • DReverse direction at all times
Report an error
Correct Answer: B. Increase somewhat as VCE increases at fixed base drive
Explanation: Base-width modulation causes collector current to depend slightly on collector-emitter voltage, giving a finite transistor output resistance.
Reference: Standard analog electronics: transistor amplifiers
Question 259
Analog ElectronicsPower Amplifiers

A class-C amplifier has a conduction angle that is typically?

  • ALess than 180 degrees
  • BExactly 180 degrees
  • CExactly 270 degrees
  • DExactly 360 degrees
Report an error
Correct Answer: A. Less than 180 degrees
Explanation: Class-C devices conduct for less than half of each input cycle and are commonly used with tuned loads in RF applications.
Reference: Standard analog electronics: power amplifiers
Question 261
Analog ElectronicsPower Amplifiers

The purpose of a heat sink attached to a power transistor is primarily to?

  • AIncrease junction temperature
  • BReduce thermal resistance from the device to ambient
  • CIncrease transistor beta exactly
  • DProvide positive feedback
Report an error
Correct Answer: B. Reduce thermal resistance from the device to ambient
Explanation: A heat sink improves heat transfer away from the device, lowering junction temperature for a given power dissipation.
Reference: Standard analog electronics: power amplifiers
Question 262
Analog ElectronicsPower Amplifiers

A transistor dissipates 2 W. If the total junction-to-ambient thermal resistance is 25 degrees C/W and ambient temperature is 30 degrees C, the estimated junction temperature is?

  • A50 degrees C
  • B55 degrees C
  • C80 degrees C
  • D105 degrees C
Report an error
Correct Answer: C. 80 degrees C
Explanation: Temperature rise = P times thermal resistance = 2×25 = 50 degrees C. Junction temperature = 30+50 = 80 degrees C.
Reference: Standard analog electronics: power amplifiers
Question 263
Analog ElectronicsActive Filters

An ideal first-order low-pass active filter has a cutoff frequency of 1 kHz. At frequencies far above cutoff, its magnitude rolls off asymptotically at approximately?

  • A-10 dB/decade
  • B-20 dB/decade
  • C-40 dB/decade
  • D+20 dB/decade
Report an error
Correct Answer: B. -20 dB/decade
Explanation: Each first-order pole contributes an asymptotic attenuation slope of about -20 dB per decade beyond the cutoff region.
Reference: Standard analog electronics: active filters
Question 266
Analog ElectronicsActive Filters

A high-pass filter ideally attenuates signals primarily?

  • AAbove its cutoff frequency
  • BBelow its cutoff frequency
  • COnly exactly at resonance
  • DAt all frequencies equally
Report an error
Correct Answer: B. Below its cutoff frequency
Explanation: A high-pass filter passes frequencies above its cutoff region while attenuating lower-frequency components.
Reference: Standard analog electronics: active filters
Question 267
Analog ElectronicsActive Filters

A band-pass filter is intended primarily to?

  • APass a selected range of frequencies and attenuate frequencies outside it
  • BPass DC only
  • CReject only one exact frequency with no passband
  • DAmplify every frequency equally
Report an error
Correct Answer: A. Pass a selected range of frequencies and attenuate frequencies outside it
Explanation: A band-pass response passes frequencies between lower and upper cutoff frequencies while attenuating frequencies outside that band.
Reference: Standard analog electronics: active filters
Question 268
Analog ElectronicsComparators & Schmitt Triggers

A comparator differs from a linear op-amp amplifier mainly because a comparator is normally intended to operate?

  • AWith its output switching between high and low states
  • BOnly with exactly unity negative feedback
  • COnly as an integrator
  • DAt zero supply voltage
Report an error
Correct Answer: A. With its output switching between high and low states
Explanation: A comparator determines which input is larger and normally drives its output toward one of two limiting states rather than operating linearly.
Reference: Standard analog electronics: comparators & schmitt triggers
Question 269
Analog ElectronicsComparators & Schmitt Triggers

The hysteresis of a Schmitt trigger is defined as the difference between its?

  • AUpper and lower switching thresholds
  • BSupply voltages only
  • CInput and output resistance
  • DOpen-loop and closed-loop gain
Report an error
Correct Answer: A. Upper and lower switching thresholds
Explanation: Hysteresis is the separation between the upper threshold voltage and lower threshold voltage.
Reference: Standard analog electronics: comparators & schmitt triggers
Question 273
Analog ElectronicsOperational Amplifiers

An op-amp has an input offset voltage of 2 mV and a closed-loop noise gain of 100. Ignoring other errors, the resulting output offset magnitude is approximately?

  • A2 mV
  • B20 mV
  • C0.2 V
  • D2 V
Report an error
Correct Answer: C. 0.2 V
Explanation: Output offset due to input offset is approximately the input offset multiplied by noise gain: 2 mV × 100 = 200 mV = 0.2 V.
Reference: Standard analog electronics: operational amplifiers
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Question 278
Analog ElectronicsTransistor Amplifiers

A common-emitter stage has an unbypassed emitter resistance RE = 1 kOhm and small-signal emitter resistance re = 25 ohm. Neglecting other effects, the emitter degeneration is dominated by?

  • AThe 25 ohm intrinsic resistance only
  • BThe 1 kOhm external emitter resistor
  • CCollector-base capacitance only
  • DSupply resistance only
Report an error
Correct Answer: B. The 1 kOhm external emitter resistor
Explanation: Because RE is much larger than re, the external emitter resistance dominates the emitter degeneration and strongly reduces gain sensitivity.
Reference: Standard analog electronics: transistor amplifiers
Question 284
Analog ElectronicsFrequency Response

If two identical noninteracting first-order amplifier stages are cascaded, the overall response near their individual cutoff frequencies is generally?

  • AExactly identical to one stage
  • BAffected because the stage responses multiply
  • CAlways flat at all frequencies
  • DIndependent of each stage response
Report an error
Correct Answer: B. Affected because the stage responses multiply
Explanation: The overall transfer magnitude is the product of individual stage magnitudes, so cascading alters the composite cutoff behavior.
Reference: Standard analog electronics: frequency response
Question 286
Analog ElectronicsFrequency Response

In a BJT amplifier, the Miller effect associated with collector-base capacitance is especially important in which configuration?

  • ACommon-emitter voltage amplifier
  • BEmitter follower with exactly unity gain
  • CCommon-base stage with no inversion
  • DDC current mirror only
Report an error
Correct Answer: A. Common-emitter voltage amplifier
Explanation: The relatively large inverting voltage gain of a common-emitter stage can multiply the effective input capacitance caused by collector-base capacitance.
Reference: Standard analog electronics: frequency response
Question 289
Analog ElectronicsActive Filters

A second-order Butterworth low-pass filter is known for having which passband characteristic?

  • AMaximally flat magnitude response
  • BEqual ripple in the passband
  • CA notch at DC
  • DInfinite gain at cutoff
Report an error
Correct Answer: A. Maximally flat magnitude response
Explanation: The Butterworth approximation is designed for a maximally flat magnitude response in the passband.
Reference: Standard analog electronics: active filters
Question 293
Analog ElectronicsFeedback Amplifiers

Which feedback topology is commonly used to obtain a voltage amplifier with increased input resistance and reduced output resistance?

  • AVoltage-series feedback
  • BVoltage-shunt feedback
  • CCurrent-series feedback only for current output
  • DCurrent-shunt feedback
Report an error
Correct Answer: A. Voltage-series feedback
Explanation: Series mixing raises input resistance and voltage sampling lowers output resistance, which is desirable for a voltage amplifier.
Reference: Standard analog electronics: feedback amplifiers
Question 294
Analog ElectronicsOscillators

For a Wien-bridge oscillator, the lead-lag feedback network has an attenuation of approximately 1/3 at resonance, so the amplifier gain required for sustained oscillation is approximately?

  • A1
  • B2
  • C3
  • D29
Report an error
Correct Answer: C. 3
Explanation: At the balance frequency the Wien network returns about one-third of the output, so the amplifier must provide a gain of approximately 3.
Reference: Standard analog electronics: oscillators
Question 297
Analog ElectronicsOscillators

A high-Q resonant circuit is characterized by?

  • AA relatively narrow bandwidth around resonance
  • BA very broad bandwidth only
  • CZero stored energy
  • DNo frequency selectivity
Report an error
Correct Answer: A. A relatively narrow bandwidth around resonance
Explanation: For a resonator, Q is inversely related to fractional bandwidth; a higher Q means sharper resonance and narrower bandwidth.
Reference: Standard analog electronics: oscillators
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