(a) BJT-OPERATING MODES & CONFIGURATIONS

1. The leakage current ICBO flows in

(a) The emitter, base and collector leads

(b) The emitter and base leads.

(c) The emitter and collector leads.

(d) The base and collector leads.

2. Early effect in BJT refers to

(a) avalanche breakdown

(b) thermal breakdown

(c) base narrowing

(d) Zener breakdown

3. The emitter of the transistor is generally doped the heaviest because it

(a) has to dissipate maximum power

(b) has to supply the charge carriers

(c) is the first region of transistor

(d) must possess low resistance

4. In a properly Biased NPN transistor most of the electrons from the emitter

(a) recombine with holes in the base

(b) recombine in the emitter its self

(c) pass through the base to the collector

(d) are stopped by the junction barrier

5. The following relationship between α and β are correct except

(a)

(b)

(c)

(d)

( )

6. The value of total collector current in a CB circuit is

(a)

(b)

(c)

(d)

7. In a transistor amplifier, the reverse saturation current ICO

(a) double for every 100 rise in temperature

(b) doubles for every 10 rise in temperature

(c) increase linearly with the temperature

(d) doubles for every 50 rise in temperature

8. The collector characteristics of a common- emitter connected transistor may be used to

find its

(a) input resistance

(b) base current

(c) output resistance

(d) voltage gain

9. Which of the following approximation is often used in electronic circuit

(a)

(b)

(c)

(d)

10. Which of the following transistor configuration circuit is much less temperature

dependent

(a) common base

(b) common emitter

(c) common collector

(d) none of the above

11. The CE amplifier circuit are preferred over CB amplifier circuit because they have

(a) lower amplification factor

(b) larger amplification factor

(c) high input resistance and low output resistance

(d) none of these

12. A transistor when connected in CE mode has

(a) a low input resistance and a low output resistance

(b) a high input resistance and high output resistance

(c) a high input resistance and low output resistance

(d) a medium input resistance and high output resistance

13. A transistor connected in common base configuration has

(a) a high input resistance and low output resistance

(b) a low input resistance and high output resistance

(c) a low input resistance and low output resistance

(d) a high input resistance and a high output resistance

Answers

1. (d) 2. (c) 3. (b) 4. (c)

5. (b) 6. (b) 7. (a) 8. (c)

9. (a) 10. (c) 11. (b) 12. (d)

13. (b)

(b) BJT CHARACTERISTICS

1. In CE configuration the output V- I characteristics are drawn by taking

(a) VCE vs. IC for constant value of IE

(b) VCE vs. IC for constant value of IB

(c) VCE vs. IC for constant value of VCB

(d) None of these

2. In CE configuration the input V-I characteristics are drawn by taking

(a) VCE vs. IC for constant value of IE

(b) VBE vs. IE for constant value of VCE

(c) VBE vs. IB for constant value of IC

(d) VBE vs. IB for constant value of VCB

3. The transistor is said to be in quiescent state when

(a) it is unbiased

(b) no current flows through it

(c) no signal is applied to the input

(d) emitter junction is just biased equal to collector junction

4. In CB configuration, the output V- I characteristics of the transistor are drawn by taking

(a) VCB vs. IC for constant IE

(b) VCB vs. IB for constant IE

(c) VCB vs. IC for constant IE

(d) VCB vs. IB for constant IE

5. When the collector junction in a transistor is biased in reverse direction and the emitter

junction in the forward direction, the transistor is said to be is the

(a) active region

(b) cutoff region

(c) saturation

(d) none of them

6. To avoid thermal runaway in the design of analog circuits, the operating point of the BJT

should be such that it satisfies the condition

(a)

(b)

(c)

(d)

7. Thermal runaway will take place if the quiescent point is such that

(a)

(b)

(c)

(d)

(UPSC Engg. Service 1999)

8. The power dissipated by a transistor approximately equals the collector current times

(a) base emitter voltage

(b) collector emitter voltage

(c) base supply voltage

(d) 0.7V

9. Leakage current in CE configuration is

(a) very high

(b) very small

(c) normal

(d) not present

10. The dc current gain in common collector configuration is given by

(a) α

(b) β

(c) β + 1

(d) α + 1

Answers

1. (b) 2. (d) 3. (c) 4. (a)

5. (a) 6. (c) 7. (d) 8. (b)

9. (a) 10. (c)

(c) BJT BIASING AND STABILIZATION

1. The dc load line of transistor circuit

(a) is a graph between IC and VCE

(b) is a graph between IC and IB

(c) does not contain the Q Point

(d) is a curved line

2. The ac load line of a transistor circuit is steeper than its dc line because

(a) ac signal sees less load resistance

(b) IC is higher

(c) input signal varies in magnitude

(d) none of the above

3. The maximum peak to peak output voltage swing is obtained when Q point of a circuit is

located

(a) near saturation point

(b) near cutoff point

(c) at the center of the load line

(d) atleast on the load line

4. The positive part of the output signal in a transistor circuit starts clipping, if Q point of

the circuit moves

(a) toward the saturation point

(b) toward the cutoff point

(c) toward the center of the load line

(d) none of the above

5. The negative part of the output signal in a transistor circuit starts clipping if the Q point

of the circuit moves

(a) toward the saturation point

(b) toward the cutoff point

(c) toward the center of the load line

(d) none of the above

6. The Q-point in a voltage amplifier is selected in the middle of the active region because

(a) it gives better stability

(b) the circuit needs a small

(c) the biasing circuit then need less number of resistors

(d) it gives distortions less output

7. The biasing circuit that gives best stability to Q point is

(a) base resistance biasing (b) feedback resistor biasing

(c) potential divider biasing (d) emitter resistor biasing

8. The potential divider biasing is used in amplifiers to

(a) limit the input ac signal going to the base

(b) reduce dc base current

(c) reduce the cost of the circuit by limiting the number of resistors

(d) make the operating point almost independent of β

9. The ideal value of stability factor of a biasing circuit is

(a) 1

(b) 5

(c) 10

(d) 100

10. The universal bias stabilization circuit is the most popular because

(a) IC does not depend on transistor characteristic

(b) its β sensitivity is low

(c) voltage divider is heavily loaded by transistor base

(d) IC equals to IE

11. Improper biasing of the transistor circuit leads to

(a) excessive heat production at collector terminal

(b) distortion in output signal

(c) faulty location of load line

(d) heavy loading of emitter terminal

12. The voltage divider biasing circuit is used in amplifiers quite often because it

(a) limits the ac signal going to base

(b) makes the operating point almost independent of β

(c) reduces the dc base current

(d) reduces the cost of the circuit

13. For a transistor amplifier with self- biasing network, the following components are used:

R1 = 4KΩ, R2 = 4KΩ and RE = 1KΩ, the approximate value of stability factor will be

(a) 4

(b) 3

(c) 2

(d) 1.5

14. Which of the following components are used for bias compensation in transistor circuit

(a) resistors

(b) rectifier diodes

(c) thermistors

(d) both (b) and (c) above

Answers

1. (a) 2. (a) 3. (c) 4. (b)

5. (a) 6. (d) 7. (c) 8. (d)

9. (a) 10. (b) 11. (b) 12. (b)

13. (b) 14. (d)

BJT Circuits (MCQs of Moderate Complexity)

1. The current ib through base of a silicon npn transistor is 1+0.1 cos (1000πt) ma. At 300K,

the rπ in the small signal model of the transistor is

ib B C

E

rπ r0

(a) 250Ω

(b) 27.5Ω

(c) 25Ω

(d) 22.5Ω

Answer (c)

The current ib through the base of a silicon npn transistor is 1+0.1 cos (10000 πt)

ma. At 300 K, the rπ in the small signal model of the transistor is given by

rπ= 𝜷. 𝒓𝒆 = 𝜷𝑽𝑻

𝑰𝑬

≅ 𝜷𝑽𝑻

𝜷𝒊𝒃=

𝑽𝑻

𝒊𝒃

𝑽𝑻 = 𝟐𝟓𝒎𝒗, 𝒊𝒃 = 𝟏𝒎𝒂

𝒓𝝅 = 𝟐𝟓 Ω

2. The amplifier circuit shown below uses a silicon transistor. The capacitors CC and CE can

be assumed to be short at signal frequency and the effect of output resistance r0can be

ignored. If CE is disconnected from the circuit, which one of the following statements is

TRUE?

AC

RiR0

CC

RC = 2.7 K RB = 800 K

CC

RE = 0.3 K CE

VS

VCC = 9V

β =100Vi

(a) The input resistance Ri increases and the magnitude of voltage gain AV decreases.

(b) The input resistance Ri decreases and the magnitude of voltage gain AV increases.

(c) Both input resistance Riand the magnitude of voltage gain AV decrease.

(d) Both input resistance Riand the magnitude of voltage gain AV increase.

Answer (a)

If CE is disconnected from the circuit, this is negative feedback. The input

impedance increases and voltage gain decreases.

3. In an ideal differential amplifier shown in the figure, a large value of (RE).

RC RC

RE

V2

–VEE

VCC

V1

(a) Increases both the differential and common-mode gains.

(b) Increases the common-mode gain only

(c) Decreases the differential-mode gain only

(d) Decreases the common-mode gain only

[GATE 2005: 2 Marks]

Answer (d)

Only common mode gain depends on RE and differential mode gain is independent

of RE

4. The cascode amplifier is a multistage configuration of

(a) CC-CB

(b) CE-CB

(c) CB-CC

(d) CE-CC

[GATE 2005: 1 Mark]

Answer (b)

Cascode amplifier provides a high input impedance with low voltage gain to ensure

minimum input miller capacitance, thus suitable for high frequency operation.

5. Assuming VCEsat = 0.2 V and β = 50, the minimum base current (IB) required to drive the

transistor in the figure to saturation is

IB

IC

1K

3V

(a) 56 μA

(b) 140 μA

(c) 60 μA

(d) 3 μA

[GATE 2004: 1 Marks]

Answer (a)

𝑽𝑪𝑬 𝒔𝒂𝒕 = 𝟎. 𝟐𝑽 & 𝛽 = 50

𝑽𝑪𝑬 = 𝑽𝑪𝑪 − 𝑰𝑪 × 𝟏𝑲

𝟎. 𝟐 = 𝟑 − 𝑰𝑪 × 𝟏𝑲

𝑰𝑪 = 𝟐. 𝟖 𝒎𝒂, 𝑰𝑩 =𝟐.𝟖 𝒎𝒂

𝟓𝟎= 𝟓𝟔 𝝁𝒂

6. Generally, the gain of a transistor amplifier falls at high frequency due to the

(a) Internal capacitance of the device

(b) Coupling capacitor at the input

(c) Skin effect

(d) Coupling capacitor at the output [GATE 2003: 1 Mark]

Answer (a)

The gain of the transistor amplifier falls at high frequency due to internal

capacitance of the device.

7. The current gain of a BJT is

(a) gmr0

(b) gm / ro

(c) gmrπ

(d) gm / rπ

[GATE 2002: 1 Mark]

The current gain of a BJT is β or hfe

IB B C

E

rπ r0

β.IB

𝒈𝒎 =𝑰𝑪

𝑽𝒊=

𝜷 𝑰𝑩

𝑰𝑩𝒓𝝅 𝒐𝒓 𝒈𝒎 =

𝜷

𝒓𝝅 𝒔𝒐 𝜷 = 𝒈𝒎𝒓𝝅

8. The current gain of a bipolar transistor drops at high frequencies because of

(a) Transistor capacitances

(b) High current effects in the base

(c) Parasitic inductive elements

(d) The Early effect

[GATE 2000: 1 Mark]

Answer (a)

The current gain of a bipolar transistor drops at high frequencies because of

transistor internal capacitances.

9. In the differential amplifier of the figure, if the source resistance of the current source IEE

is infinite, then common-mode gain is

R R

–VEE

VCC

IEE

Vin1 Vin2

(a) Zero

(b) Infinite

(c) Indeterminate

(d) (Vin1 + Vin2) + 2VT

[GATE 2000: 1 Mark]

Answer (a)

The Common mode gain, 𝑽𝑪 = 𝑨𝑪𝑽𝒊 (𝑽𝒊𝟏= 𝑽𝒊𝟐

= 𝑽𝒊). If the source resistance of

current source (Rs) is infinite then due to symmetry common mode gain VC is zero.

10. In the cascode amplifier shown in the figure, if the common-emitter stage (Q1) has a trans

conductance gm1 and the common base stage (Q2) has a trans conductance gm2 then the

overall trans conductance g(=i0 / Vi) of the cascode amplifier is

Vi

V0

Q1

Q2

RL

i0

ic1

(a) gm1

(b) gm2

(c) gm1 / 2

(d) gm2 / 2

[GATE 1999: 1 Mark]

Answer (a)

Q1 has transconductance𝒈𝒎𝟏

Q2 has transconductance𝒈𝒎𝟐

Overall transconductance𝒈 =𝒊𝟎

𝑽𝒊

𝒊𝟎 = 𝒊𝑬𝟐= 𝒊𝑪𝟏

𝒔𝒐 𝒈 = 𝒈𝒎𝟏

11. the unit of q / KT are

(a) V

(b) V-1

(c) J

(d) J / K

[GATE 1998: 1 Mark]

Answer (b)

Thermal voltage = 𝑽𝑻 =𝑲𝑻

𝒒

12. A multistage Amplifier has a low-pass Response with three real poles at s = -ω1, –ω2 and

ω 3 The approximate overall bandwidth B of the Amplifier will be given by

(a) 𝐵 = ω1 + ω2 + ω3

GATE Analog Circuits Objective TypeQuestions With Answers (Electronics

Engineering)

Publisher : Faculty Notes Author : Panel Of Experts

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