This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Colpitts Oscillator-1”.
1. Which type of feedback is used by Colpitts oscillator?
a) Voltage series feedback
b) Current series feedback
c) Voltage shunt feedback
d) Current shunt feedback
View Answer
Explanation: Voltage series feedback is used in Colpitts oscillator. In voltage series feedback a part of output voltage is fed back to input.
2. Which component of Colpitts oscillator is used in feedback system?
a) Inductor
b) Resistor
c) Capacitor
d) Transistor
View Answer
Explanation: A capacitor with a center tap or simply two capacitors in parallel to an inductor, acting as a voltage divider, acts as the feedback system, providing feedback to the base of the amplifying transistor. Oscillations across the capacitor are applied at the base-emitter junction and appear across the collector as an amplified output.
3. Which of the following network is used to give feedback to transistor?
a) Inductive fixed bias
b) Capacitive fixed bias
c) Inductive voltage divider
d) Capacitive voltage divider
View Answer
Explanation: Capacitive voltage divider network is used for giving positive feedback in Colpitts oscillator. Oscillations across the capacitor are applied at the base-emitter junction and appear across the collector as an amplified output. The amount of feedback depends on the ratio of the two capacitors being used.
4. How many capacitors are there in the tank circuit of Colpitts oscillator?
a) 1
b) 2
c) 3
d) 0
View Answer
Explanation: There are two capacitors in the tank circuit of Colpitts oscillator and it is given for voltage division.
5. How many inductors are there in the tank circuit?
a) 1
b) 2
c) 3
d) 0
View Answer
Explanation: There are one inductor in the tank circuit of Colpitts oscillator and it is given for oscillation.
6. Capacitive circuit configuration in Colpitts oscillator improves _____________
a) Bulkiness
b) Frequency stability
c) Impedance
d) Appearance
View Answer
Explanation: Capacitive circuit in the colpitt oscillator improves frequency stability. An additional 180° phase shift is provided by the capacitive tank circuit, providing no phase shift to the output. By changing tap position or the value of capacitors in the tank circuit, we can change feedback amount.
7. Active element used in Colpitts oscillator is _________
a) Cell
b) Voltage regulator
c) Diode
d) Transistor
View Answer
Explanation: The active element used in Colpitts oscillator is transistor and it is used for amplification of weak oscillator signals.
8. RFC choke present in Collpitts oscillatory circuit is for _________
a) High reactance to oscillation
b) Low reactance to oscillation
c) Variable reactance to oscillation
d) Biasing to oscillation
View Answer
Explanation: RFC choke present in Colpitts oscillator is to provide high reactance to AC oscillation and low reactance to DC supply to improve performance.
9. RFC choke is placed in Colpitts oscillator instead of resistor is to provide _________
a) High impedance to DC
b) High resistance to DC
c) Low resistance to DC
d) Less bulkiness
View Answer
Explanation: RFC choke present in Colpitts oscillator is to provide high reactance to AC oscillation and low reactance to DC supply to improve performance. If resistor is used there will be some power loss in DC biasing which is unnecessary.
10. Resistors are provided in Colpitts circuit is to __________
a) Provide high impedance to oscillation
b) Bias transistor
c) Provide stability for tank circuit
d) increase impedance for oscillation
View Answer
Explanation: Resistors are used to bias transistor to its DC operating point. Capacitor divider circuit provides input bias to the amplifying element.
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