This set of Electronic Devices and Circuits Puzzles focuses on “CE Amplifier with an Emitter Resistance”.
1. For a common-emitter amplifier, the purpose of swamping is ________
a) to minimize gain
b) to reduce the effects of r’e
c) to maximize gain
d) no purpose
Explanation: A swamping resistor is an unbiased resistance in the emitter (re) circuit of a common-emitter amplifier. The swamping resistor stabilizes the voltage gain and reduces distortion.
2. What is the use of coupling capacitors in CE amplifier?
a) blocks dc
b) pass ac
c) reduce distortion
d) pass ac & blocks dc
Explanation: In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked. This technique helps to isolate the DC bias settings of the two coupled circuits.
3. CE amplifier is mostly preferred in amplifier circuits because _________
a) it provides better voltage and current gain
b) of low output impedance
c) of high output impedance
d) it has better Q-point
Explanation: The common emitter configuration(CE) provides maximum voltage and current gain. The other configurations provide either high current gain or voltage gain but not both for a BJT. That’s why CE amplifier is always preferred and hence does the choice of CE becomes obvious.
4. Which type of biasing is used in CE amplifier?
a) Fixed bias
b) Collector to base bias
c) Voltage divider bias
d) Emitter bias
Explanation: The single stage common emitter amplifier uses biasing commonly called “Voltage Divider Biasing”. This type of biasing arrangement uses two resistors as a potential divider network across the supply with their center point supplying the required Base bias voltage to the transistor.
5. What is the correct phase shift in CE amplifier?
a) 45 degrees
b) 180 degrees
c) 60 degrees
d) 120 degrees
Explanation: The negative alternation of an AC signal will cause a decrease in the base current. This action then causes a corresponding decrease in emitter current through RL(load). The output signal of a common- emitter amplifier is therefore 180 degrees out of phase with the input signal.
6. The use of by-pass capacitor in CE amplifier is _________
a) to increase voltage gain
b) to increase negative feedback
c) for decreasing the frequency
d) to block dc
Explanation: When an emitter resistance is added in a CE amplifier, its voltage gain is reduced, but the input impedance increases. Whenever bypass capacitor is linked in parallel with an emitter resistance, the voltage gain of CE amplifier increases.
7. In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked.
Explanation: A coupling capacitor allows ac signal to pass from one circuit to the other. This technique helps to isolate the DC bias settings of the two coupled circuits.
8. When the signal is applied, the ratio of change of collector current to the ratio of change of base current is called_________
a) dc current gain
b) ac current gain
c) base current amplification factor
d) emitter current amplification factor
Explanation: The ac current gain is given by β=∆IC/∆IB. When the signal is applied, the ratio of change of collector current to the ratio of change of base current is called ac current gain.
9. In CE configuration, if the voltage drop across 6kΩ resistor connected in the collector circuit is 6V. Find the value of IB when β=50.
Explanation: IC=V across RL/RL=5V/5KΩ=1mA
10. The___________ configuration is used frequently for impedance matching.
a) fixed bias
b) voltage- divider
c) emitter follower
d) collector feedback
Explanation: The emitter follower configuration is mostly used as a voltage buffer. These configurations are extensively used in impedance matching applications because of their high input impedance.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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