Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
A tunnel diode exhibits negative resistance in a specific voltage range due to:
Answer: D
Tunnel diodes show negative differential resistance due to quantum tunneling through the narrow depletion region created by heavy doping. This occurs in forward bias and enables their use as oscillators and amplifiers.
Q.2Hard
For a BJT in saturation, the relationship between base current and collector current is:
Answer: B
In saturation, both junctions are forward biased. The collector current becomes less than β × Ib because the transistor is no longer in linear region. Excess base current doesn't proportionally increase collector current.
Q.3Hard
Which of the following statements about CMOS logic is correct?
Answer: B
CMOS (Complementary MOS) has very low static power dissipation because complementary P and N transistors prevent steady-state current paths. However, dynamic power dissipation increases with switching frequency due to capacitive charging/discharging.
Q.4Hard
In a power MOSFET, the on-resistance (RDS_on) is primarily determined by:
Answer: C
RDS_on consists of channel resistance and drift region resistance. For power MOSFETs, drift region (epitaxial layer) dominates. Minimizing drift region thickness reduces RDS_on but decreases breakdown voltage, creating a design trade-off.
Q.5Hard
A Schottky diode offers advantages over PN junction diodes primarily because of:
Answer: C
Schottky diodes have metal-semiconductor junctions with lower forward voltage (0.3-0.5V vs 0.7V for silicon) and faster switching due to absence of minority carrier storage. This makes them ideal for high-frequency and high-speed switching applications.
Q.6Hard
What is the significance of Early voltage (VA) in a BJT?
Answer: C
Early voltage (VA) represents the output resistance (ro = VA/Ic) of a BJT. Larger VA indicates steeper output characteristics, meaning collector current is more independent of collector-emitter voltage, indicating better current source behavior.
Q.7Hard
In integrated circuit design, what does the term 'aspect ratio' refer to in MOSFETs?
Answer: B
Aspect ratio (W/L) is a fundamental design parameter in MOSFETs affecting current capability and switching speed. Higher W/L provides larger current capacity and faster transitions, crucial for circuit optimization and performance tuning.
Q.8Hard
The transconductance (gm) of a MOSFET in saturation region is given by:
Answer: C
Transconductance gm = ∂ID/∂VGS = ID/(VGS - VT) at saturation, fundamental small-signal parameter.
Q.9Hard
The punch-through effect in a BJT occurs when:
Answer: B
Punch-through occurs when CBJ depletion width extends to base contact, causing base resistance to vanish and uncontrolled current flow.
Q.10Hard
The body effect in MOSFETs causes which of the following?
Answer: C
Body effect (substrate bias) increases VT due to back-bias effect and decreases output impedance; VT = VT0 + √(2εqNa/Cox)·φt term.
Q.11Hard
In a Gunn diode, negative resistance occurs due to:
Answer: B
Gunn effect: electrons transfer from high-mobility Γ valley to low-mobility L valley at threshold field, causing dI/dV < 0 (negative resistance).
Q.12Hard
The Miller effect in a common-emitter BJT amplifier causes:
Answer: B
Miller effect: CBE capacitance reflected to input = CμC·(1+|Av|); dominates high-frequency response and limits bandwidth in CE configuration.
Q.13Hard
The avalanche breakdown voltage (BV) in a reverse-biased junction approximately follows:
Answer: C
Breakdown voltage BV ∝ ND^(-43) approximately; lower doping increases depletion width, requiring higher field and higher voltage for breakdown.
Q.14Hard
When a BJT is used as a switch in saturated condition, the overdrive factor is defined as:
Answer: A
Overdrive factor β = IB(actual) / IB(min) ensures transistor stays saturated even with parameter variations.
Q.15Hard
A JFET in pinch-off condition means:
Answer: A
At pinch-off, VGS reaches VP (pinch-off voltage), channel closes, and further VDS increase has minimal effect on ID (saturation region).
Q.16Hard
In practical MOSFET applications for RF circuits, which parasitic effect limits frequency response most?
Answer: B
The gate-drain capacitance (Cgd) creates Miller effect, which effectively multiplies the capacitive reactance in feedback, severely limiting high-frequency gain.
Q.17Hard
The noise figure of a BJT amplifier at low frequencies is primarily determined by:
Answer: B
At low frequencies, shot noise associated with base current (IB) dominates, following Poisson statistics: i²n = 2q×IB×Δf.
Q.18Hard
In a MOSFET differential amplifier, the common-mode gain is reduced by using:
Answer: C
Current mirror loads increase output impedance, while source degeneration resistors provide common-mode feedback, both reducing common-mode gain.
Q.19Hard
The avalanche multiplication factor M in reverse-biased junction is expressed as:
Answer: A
The avalanche factor M = 1/(1-(VR/BV)ⁿ) shows multiplication increases exponentially as reverse voltage approaches breakdown voltage BV, where n≈3-6.
Q.20Hard
The transconductance (g_m) of a MOSFET in saturation is given by:
