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BJT and FET Biasing and Amplifiers

Total questions: 50

Worksheet time: 25mins

Name
Class
Date
1.

The DC load line of a BJT is obtained from:

a)

Input characteristics

b)

Output characteristics with external load resistance

c)

Transfer characteristics

d)

None of these

2.

The intercepts of DC load line are given by:

a)

VCE = VCC, IC = 0 and VCE = 0, IC = VCC/RC

b)

VCE = 0, IC = 0

c)

Both A and B

d)

None

3.

The AC load line is different from DC load line because:

a)

AC analysis ignores supply voltage

b)

It includes load resistance seen by AC signal

c)

It passes through the Q-point

d)

All of the above

4.

For VCC = 10V, RC = 2kΩ, draw DC load line intercepts.

a)

(0, 5mA) & (10V, 0)

b)

(0, 10mA) & (5V, 0)

c)

(0, 2mA) & (20V, 0)

d)

None

5.

The operating point of a BJT is defined by:

a)

IB and IE

b)

VBE and VCE

c)

IC and VCE

d)

Only VCC

6.

If Q-point lies at the center of load line, amplifier has:

a)

Maximum distortion

b)

Minimum distortion

c)

Cut-off

d)

Saturation

7.

Wrong positioning of Q-point causes:

a)

Distortion in output

b)

Increased stability

c)

Linear amplification

d)

None

8.

Which biasing method provides maximum stability?

a)

Fixed bias

b)

Collector-to-base bias

c)

Voltage divider bias

d)

None

9.

In fixed bias circuit, base resistor is connected between:

a)

Base and emitter

b)

Base and collector

c)

Base and Vcc

d)

Collector and emitter

10.

Voltage divider bias provides stability because:

a)

It reduces dependency on β

b)

It increases current gain

c)

It reduces supply voltage

d)

None

11.

In collector-to-base bias:

a)

Negative feedback improves stability

b)

Positive feedback improves gain

c)

No feedback

d)

None

12.

Stability factor (S) is defined as:

a)

∂IC/∂β

b)

∂IC/∂ICO

c)

∂IC/∂VBE

d)

All of the above

13.

In fixed bias, stability factor is approximately:

a)

1

b)

β

c)

(β+1)

d)

Large

14.

The best biasing method with least stability factor is:

a)

Fixed bias

b)

Voltage divider bias

c)

Emitter bias without resistor

d)

None

15.

Bias compensation uses:

a)

Diode in series with base

b)

Thermistor

c)

Both A and B

d)

None

16.

Thermal runaway occurs due to:

a)

Increase in β with temperature

b)

Increase in ICO with temperature

c)

Both A and B

d)

None

17.

For β = 100, ICO = 20μA, find IC if IB = 40μA.

a)

4.0 mA

b)

4.02 mA

c)

0.4 mA

d)

40 mA

18.

To avoid thermal runaway, circuits must use:

a)

Negative feedback through emitter resistor

b)

Larger collector resistance

c)

Higher Vcc

d)

None

19.

A silicon diode used in bias compensation is placed:

a)

Far away from transistor

b)

Thermally coupled with transistor

c)

Electrically isolated

d)

None

20.

In JFET, the drain current equation is:

a)

ID = IDSS(1 - VGS/VP)^2

b)

ID = β(VGS - VT)^2

c)

Both A and B

d)

None

21.

Self-bias method for JFET uses:

a)

Resistor at drain

b)

Resistor at source

c)

Resistor at gate

d)

None

22.

For JFET with IDSS = 10mA, VP = -4V, find ID at VGS = -2V.

a)

2.5 mA

b)

5 mA

c)

7.5 mA

d)

10 mA

23.

MOSFET transfer characteristic in saturation is:

a)

ID = k(VGS - VT)^2

b)

ID = IDSS(1 - VGS/VP)^2

c)

ID = VDS/RD

d)

None

24.

In MOSFET biasing, a large value of RG is used to:

a)

Provide gate current

b)

Ensure negligible gate current

c)

Increase transconductance

d)

None

25.

For n-channel MOSFET, k = 0.5mA/V², VT = 2V, find ID when VGS = 6V.

a)

2 mA

b)

4 mA

c)

8 mA

d)

1 mA

26.

The most commonly used amplifier configuration for voltage amplification is:

a)

Common Base

b)

Common Emitter

c)

Common Collector

d)

Darlington Pair

27.

The input impedance of a common collector amplifier is:

a)

Very high

b)

Very low

c)

Medium

d)

Equal to load resistance

28.

The output impedance of a common collector amplifier is:

a)

High

b)

Low

c)

Equal to Rc

d)

Infinite

29.

Current gain in common base configuration is approximately:

a)

β

b)

α (≈ 1)

c)

0

d)

∞

30.

In hybrid model, h11 represents:

a)

Input impedance

b)

Reverse voltage gain

c)

Forward current gain

d)

Output admittance

31.

In h-parameter model, h21 corresponds to:

a)

Current gain (IC/IB)

b)

Reverse current gain

c)

Voltage gain

d)

Input impedance

32.

For CE amplifier, approximate voltage gain is:

a)

-h21 × (Rc / hie)

b)

h21 × (hfe / hoe)

c)

Rc / hie

d)

None

33.

In CE amplifier, if β = 100, Rc = 2kΩ, Re = 500Ω, the voltage gain is approximately:

a)

-4

b)

-20

c)

-200

d)

-400

34.

For a BJT amplifier, Rc = 4kΩ, hie = 1kΩ, hfe = 50. Find approximate voltage gain.

a)

-100

b)

-200

c)

-50

d)

-400

35.

The current gain of common collector amplifier is approximately:

a)

α

b)

β

c)

(β + 1)

d)

0

36.

Which amplifier has a phase shift of 180° between input and output?

a)

CE amplifier

b)

CB amplifier

c)

CC amplifier

d)

All of these

37.

The input impedance of CB amplifier is:

a)

Very low

b)

Very high

c)

Moderate

d)

Infinite

38.

The output impedance of CE amplifier is mainly controlled by:

a)

Rc

b)

Re

c)

Vcc

d)

β

39.

The amplifier with highest input resistance is:

a)

CE

b)

CB

c)

CC

d)

Differential pair

40.

In cascaded amplifiers, overall gain is equal to:

a)

Sum of individual gains

b)

Product of individual gains

c)

Average of individual gains

d)

Difference of individual gains

41.

If two CE amplifiers with gains 50 and 40 are cascaded, overall gain is:

a)

2000

b)

90

c)

10

d)

200

42.

The main advantage of cascading is:

a)

Increased bandwidth

b)

Increased gain

c)

Reduced distortion

d)

None

43.

A differential amplifier amplifies:

a)

Common-mode signals

b)

Differential signals

c)

Both equally

d)

None

44.

Differential gain is defined as:

a)

Output / Common input

b)

Output / Differential input

c)

Input / Output

d)

None

45.

Common-mode gain should be:

a)

Very high

b)

Very low

c)

Equal to differential gain

d)

None

46.

For a differential amplifier, differential gain = 200, common-mode gain = 0.5. Find CMRR.

a)

100

b)

200

c)

400

d)

600

47.

CMRR in dB is given by:

a)

20 log (Ad / Ac)

b)

10 log (Ad / Ac)

c)

20 log (Ac / Ad)

d)

None

48.

A high CMRR indicates:

a)

Poor common-mode rejection

b)

Good common-mode rejection

c)

High distortion

d)

None

49.

In CS amplifier, voltage gain is given by:

a)

-gm Rd

b)

gm Rd

c)

1/gm

d)

Rd/gm

50.

For a FET with gm = 2 mA/V, Rd = 5kΩ, find voltage gain.

a)

-5

b)

-10

c)

-20

d)

-15