Electronic Circuits I Set 5 MCQs

Q1 | In a Single Input Balanced Output Differential amplifier, given VCC=15v, RE = 3.9kΩ, VCE=2.4 v and re=250Ω. Determine Voltage gain

26
56
38
61

Answer: 26

Explaination:
in single input balance output amplifier,

Q2 | For the difference amplifier which of the following is true?

it responds to the difference between the two signals and rejects the signal that are common to both the signal
it responds to the signal that are common to the two inputs only
it has a low value of input resistance
the efficacy of the amplifier is measured by the degree of its differential signal to the preference of the common mode signal

Answer: it responds to the difference between the two signals and rejects the signal that are common to both the signal

Explaination:
all the statements are not true except for the fact that it responds only when there is difference between two signals only.

Q3 | The problem with the single operational difference amplifier is its

high input resistance
low input resistance
low output resistance
none of the mentioned

Answer: low input resistance

Explaination:
due to low input resistance a large part of the signal is lost to the source’s internal resistance.

Q4 | For the circuit shown below express v0 as a function of v1 and v2.

v0 = v1 + v2
v0 = v2 – v1
v0 = v1 – v2 d) v0 = -v1 – v2

Answer: v0 = v2 – v1

Explaination:
considering the fact that the potential at the input terminals are identical and proceeding we obtain the given result.

Q5 | Determine Ad and Ac for the given circuit.

ac = 0 and ad = 1
ac ≠ 0 and ad = 1
ac = 0 and ad ≠ 1
ac ≠ 0 and ad ≠ 1

Answer: ac = 0 and ad = 1

Explaination:
consider the fact that the potential at the input terminals are identical and obtain the values of v1 and v2. thus obtain the value of vd and vc.

Q6 | Determine the voltage gain for the given circuit known that R1 = R3 = 10kΩ abd R2 = R4 = 100kΩ.

1
10 c) 100 d) 1000

Answer: 10 c) 100 d) 1000

Explaination:
voltage gain is 100/10.

Q7 | What is trans-conductance?

ratio of change in drain current to change in collector current
ratio of change in drain current to change in gate to source voltage
ratio of change in collector current to change in drain current
ratio of change in collector current to change in gate to source voltage

Answer: ratio of change in drain current to change in gate to source voltage

Explaination:
the change in drain current which is resulted due to change in gate to source voltage in a fet is measured by trans- conductance. this is termed as trans because it provides relationship between input and output quantity.

Q8 | What is the value of trans conductance?

1
2 c) 0.1
d) 0.01

Answer: d) 0.01

Explaination:
trans-conductance= change in drain current/ change in gate to source voltage

Q9 | 002. What is the value ofgm?

1
2
0.002

Answer: 0.002

Explaination:
gm = change in drain current/ change in gate to source voltage gm = slope of vgs vs id gm = 0.002.

Q10 | Find the maximum value of gm for FET with IDSS=10mA, Vp=-2V, VGS=5V?

10ms
20ms
1ms

Answer: 10ms

Explaination:
gm0=2idss/

Q11 | A FET has IDSS=4ID and gm0 = 10mS then gm =

10ms
20ms
5ms
14ms

Answer: 5ms

Q12 | Determine the value of output impedance for JFET, if the value of gm =1mS?

1kohm
0
100kohm
5kohm

Answer: 1kohm

Explaination:
output impedance=inverse of trans conductance

Q13 | In a small signal equivalent model of an FET, What does gm VGS stand for?

a pure resistor
voltage controlled current source
current controlled current source
voltage controlled voltage source

Answer: voltage controlled current source

Explaination:
for fet, the voltage is applied across the gate and source to control the drain current, hence while writing small signal model of an fet, on the output side gm vgs represents a current source which can be controlled by the input voltage vgs.

Q14 | Given yfs = 3.6mS and yos = 0.02mS, determine r0?

100kohm
50mohm
50kohm
20kohm

Answer: 50kohm

Explaination:
r0=1/yos

Q15 | Which of the following statement is incorrect?

output of ce amplifier is out of phase with respect to its input
cc amplifier is a voltage buffer
cb amplifier is a voltage buffer
ce amplifier is used as an audio (low frequency) amplifier

Answer: cb amplifier is a voltage buffer

Explaination:
the output of the ce amplifier has a phase shift of 180o with respect to the input. the cc amplifier has av≅1, thus it is a voltage buffer. however, the cb amplifier has a large voltage gain, and its current gain ai≅1, thus it is a current buffer. ce amplifier has an application has an audio amplifier.

Q16 | Given hfe = 60, hie=1000Ω, hoe = 20μ Ω–, hre = 2 * 10-4. Find the current gain of the BJT, correct up to two decimal points.

– 58.44
-59.21
– 60.10
– 60.00

Answer: – 58.44

Explaination:
current gain, ai = – hf / (1 +

Q17 | Consider the circuit. Given hfe = 50, hie = 1200Ω. Find voltage gain.

– 278
-277.9
– 300
– 280

Answer: – 278

Explaination:
voltage gain = av = - hferl’/hie

Q18 | Given that IB = 5mA and hfe = 55, find load current.

28ma
280ma
2.5a
2a

Answer: 280ma

Explaination:
in given circuit, which is an emitter follower, current gain = 1 + hfe

Q19 | Consider the following circuit, where source current = 10mA, hfe = 50, hie = 1100Ω, then for the transistor circuit, find output resistance RO and input resistance RI.

ro = 0, ri = 21Ω
ro = ∞, ri = 0Ω
ro = ∞, ri = 21Ω
ro = 10, ri = 21Ω

Answer: ro = ∞, ri = 21Ω

Explaination:
since hoe is not given, we can consider it to be small; i.e 1/hoe is neglected, open circuited. hence output resistance ro =

Q20 | For the given circuit, input resistance RI = 20Ω, hfe = 50. Output resistance = ∞. Find the new values of input and output resistance, if a base resistance of 2kΩ is added to the circuit.

ri = 20Ω, ro = ∞
ri = 20Ω, ro = 2kΩ
ri = 59Ω, ro = ∞
ri = 59Ω, ro = 2kΩ

Answer: ri = 59Ω, ro = ∞

Explaination:
ri = 20k = hie/(1+hfe) = hie/51 hie =1020 Ω

Q21 | If source resistance in an amplifier circuit is zero, then voltage gain (output to input voltage ratio) and source voltage gain (output to source voltage ratio) are the same.

true
false

Answer: true

Explaination:
when a source resistance rs is present, the voltage gain with respect to source becomes

Q22 | The Differential output of the difference amplifier is the amplification of

difference between the voltages of input signals
difference between the output of the each transistor
difference between the supply and the output of the each transistor
all of the mentioned

Answer: difference between the voltages of input signals

Explaination:
none.

Q23 | The inputs to the differential amplifier are applied at

at x and y
at the gates of m1 and m2
all of the mentioned
none of the mentioned

Answer: at the gates of m1 and m2

Explaination:
none.

Q24 | In Common Mode Differential Amplifier, the outputs Vout1 and Vout2 are related as:

vout2 is in out of phase with vout1 with same amplitude
vout2 and vout1 have same amplitude but the phase difference is 90 degrees
vout1 and vout2 have same amplitude and are in phase with each other and their respective inputs
vout1 and vout2 have same amplitude and are in phase with each other but out of phase with their respective inputs

Answer: vout1 and vout2 have same amplitude and are in phase with each other but out of phase with their respective inputs

Explaination:
none.

Q25 | In a small signal differential gain vs input CM level graph, the gain decreases after V2 due to:

as the input voltage increases, the output will be clipped
when the input voltage to the transistors are high, the transistor enters saturation region and increases the current, which inturn decreases the output voltage = vdd – rd.iss
when common mode voltage is greater than or equal to v2, the input transistors enter triode region, the gain begins to fall
increasing the input voltage beyond v2 causes the gate oxide to conduct and the gain is reduced

Answer: when common mode voltage is greater than or equal to v2, the input transistors enter triode region, the gain begins to fall

Explaination:
none.