# Electronic Devices and Circuits Questions and Answers – BJT in Amplifier Design

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “BJT in Amplifier Design”.

1. Find the maximum allowed output negative swing without the transistor entering saturation, and
a) 1.27 mV
b) 1.47 mV
c) 1.67 mV
d) 1.87 mV

2. The corresponding maximum input signal permitted is
a) 1.64 mV
b) 1.74 mV
c) 1.84 mV
d) 1.94 mV

Explanation: If we assume linear operation right to saturation we can use the gain Av to calculate the maximum input signal. Thus for an output swing ∆ Vo = 0.8 we have
∆ Vi = ∆ Vo / Av = -0.7 / -360 = 1.94 mV.

3. For the amplifier circuit in the below figure with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to Ic. Find the voltage gain.
a) 100 Ic
b) 200 Ic
c) 400 Ic
d) 800 Ic

4. For the amplifier circuit in the below figure with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to Ic. The maximum possible positive output signal swing as determined by the need to keep the transistor in the active region.
a) 9.7 + Ic
b) 9.7 – Ic
c) 10.3 + Ic
d) 10.3 – Ic

Explanation: Assuming the output voltage Vo = 0.3v is the lowest Vce to stay out of saturation.
Vo = 0.3 = 10 – IcRc
= 10 – IcRc + ∆Vo
∆ Vo = -10 + 0.3 + Ic*1.

5. For the amplifier circuit in the below figure with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to Ic. The maximum possible negative output signal swing as determined by the need to keep the transistor in the active region.
a) 0.1 Ic
b) Ic
c) 10 Ic
d) 100 Ic

Explanation: Maximum output voltage before the Transistor is cutoff.
Vce + ∆Vo = Vcc
∆Vo = Vcc – Vce
= 10 – 10 + 10 Ic
= 10 Ic.
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6. The transistor in the circuit below is biased at a dc collector current of 0.5 mA. What is the voltage gain? a) -1 V/V
b) -10 V/V
c) -100 V/V
d) -1000 V/V

7. For a BJt Vt is 5 V, Rc = 1000 ohm and bias current Ic is 12 mA. The value of the voltage gain is __________
a) -1.2 V/V
b) -2.4 V/V
c) -3.6 V/V
d) -4.8 V/V

Explanation: Voltage gain is (Ic X Rc) / Vt.

8. For the BJT amplifier circuit with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to 5 mA. The value of the voltage gain is _______________
a) -2 V/V
b) -4 V/V
c) -10 V/V
d) -20 V/V

Explanation: The voltage is 400 X Ic where Ic is 5 mA.

9. For the BJT amplifier circuit with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to 5 mA. The maximum possible positive output signal swing as determined by the need to keep the transistor in the active region.
a) -1.7 V
b) -2.7 V
c) -3.7 V
d) -4.7 V

Explanation: The maximum voltage swing is given by -10 + 0.3 + (Ic X Rc). Putting Ic as 5 mA, we get -4.7 mV.

10. For the BJT amplifier circuit with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to 5 mA. The maximum possible negative output signal swing as determined by the need to keep the transistor in the active region.
a) 0.5 V
b) 1 V
c) 5 V
d) 10 V

Explanation: It is given by -10 + 10 + (Ic X Rc). Putting Ic as 5 mA we get 5V.

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