A germanium BJT has a base-emitter voltage VBE = 0.3 V in forward bias. Compared to a silicon BJT with VBE = 0.7 V, which statement is correct?

The correct answer is A: Germanium has lower bandgap energy and requires less forward voltage to turn on. Germanium has bandgap Eg ≈ 0.67 eV versus silicon's 1.12 eV. Lower bandgap requires less voltage to forward bias. However, silicon is preferred due to better temperature stability and lower leakage current.

A 4-bit Ripple Carry Adder has a total propagation delay of 12 ns. If each full adder stage has a propagation delay of 3 ns, what is the delay for carry propagation?

The correct answer is B: 9 ns. In a 4-bit ripple carry adder, the carry must propagate through 3 stages (from FA1 to FA4), giving delay = 3 × 3 ns = 9 ns.

What is the setup time in a flip-flop?

The correct answer is B: Minimum time input must be stable before clock edge. Setup time (tsu) is the minimum duration the input signal must remain stable and valid before the active clock edge for reliable capture and state change

At what frequency does the gain of a RC coupled amplifier reduce to 70.7% of its mid-band gain?

The correct answer is B: At cutoff frequency (-3dB point). The -3dB cutoff frequency is where the magnitude of gain reduces to 1/√2 (≈ 70.7%) of maximum gain. This defines the bandwidth of the amplifier.

Which of the following is a volatile memory?

The correct answer is C: RAM. RAM (Random Access Memory) is volatile and loses all data when power is removed. ROM, EPROM, and Flash memory are non-volatile.

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Electronics (ECE)

Analog/digital electronics, communication

78 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–78 of 78

Topics in Electronics (ECE)

All Electronic Devices 100 Digital Electronics 100 Analog Circuits 100 Signals & Systems 100

Q.71 Hard Electronic Devices

The transconductance (gm) of a MOSFET in saturation region is given by:

A gm = μnCox(W/L)(VGS - VT)²

B gm = 2μnCox(W/L)ID

C gm = ID/(VGS - VT)

D gm = (VGS - VT)/ID

Correct Answer: C. gm = ID/(VGS - VT)

EXPLANATION

Transconductance gm = ∂ID/∂VGS = ID/(VGS - VT) at saturation, fundamental small-signal parameter.

Test

Q.72 Hard Electronic Devices

In integrated circuit design, what does the term 'aspect ratio' refer to in MOSFETs?

A The ratio of gate voltage to drain voltage

B The ratio of channel width (W) to channel length (L)

C The ratio of oxide thickness to gate length

D The ratio of drain current to gate current

Correct Answer: B. The ratio of channel width (W) to channel length (L)

EXPLANATION

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.

Test

Q.73 Hard Electronic Devices

What is the significance of Early voltage (VA) in a BJT?

A It represents the barrier potential of the junction

B It indicates the thermal voltage of the transistor

C It characterizes the slope of output characteristics (channel length modulation effect)

D It defines the maximum frequency of operation

Correct Answer: C. It characterizes the slope of output characteristics (channel length modulation effect)

EXPLANATION

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.

Test

Q.74 Hard Electronic Devices

A Schottky diode offers advantages over PN junction diodes primarily because of:

A Higher forward voltage drop

B Slower switching speed

C Lower forward voltage drop and faster switching speed

D Better reverse recovery characteristics

Correct Answer: C. Lower forward voltage drop and faster switching speed

EXPLANATION

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.

Test

Q.75 Hard Electronic Devices

In a power MOSFET, the on-resistance (RDS_on) is primarily determined by:

A Gate oxide thickness

B Channel length modulation

C Drift region resistance and channel resistance

D Gate-drain capacitance

Correct Answer: C. Drift region resistance and channel resistance

EXPLANATION

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.

Test

Q.76 Hard Electronic Devices

Which of the following statements about CMOS logic is correct?

A High static power dissipation at rest

B Low static power dissipation but higher dynamic power dissipation

C Requires less substrate area than NMOS

D Cannot operate at high frequencies

Correct Answer: B. Low static power dissipation but higher dynamic power dissipation

EXPLANATION

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.

Test

Q.77 Hard Electronic Devices

For a BJT in saturation, the relationship between base current and collector current is:

A Ic = β × Ib (normal relationship holds)

B Ic < β × Ib (actual current is less than theoretical)

C Ic > β × Ib (actual current exceeds theoretical)

D Ic is independent of Ib

Correct Answer: B. Ic < β × Ib (actual current is less than theoretical)

EXPLANATION

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.

Test

Q.78 Hard Electronic Devices

A tunnel diode exhibits negative resistance in a specific voltage range due to:

A Reverse bias condition

B Quantum mechanical tunneling effect

C High doping concentration creating a narrow depletion region

D All of the above

Correct Answer: D. All of the above

EXPLANATION

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.

Test

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