Test: Common Collector Configuration - Electronics and Communication Engineering (ECE) MCQ

• The common collector transistor circuit configuration gains its name from the fact that the collector circuit is common to both input and output circuits, the base is associated with only the input, and then the emitter with the output only.
• The other name for the common collector is emitter follower. This name is derived from the fact that the emitter voltage "follows" that of the base circuit - the circuit has unit voltage gain.
• The emitter follower transistor amplifier has a very straightforward circuit. The base is connected to the previous stage, and often this may be directly connected as this can save on additional bias resistors which lower the input impedance and hence increase the loading to the previous stage.

• The common collector transistor circuit configuration gains its name from the fact that the collector circuit is common to both input and output circuits, the base is associated with only the input, and then the emitter with the output only.
• The other name for the common collector is emitter follower. This name is derived from the fact that the emitter voltage "follows" that of the base circuit - the circuit has unit voltage gain.
• The emitter follower transistor amplifier has a very straightforward circuit. The base is connected to the previous stage, and often this may be directly connected as this can save on additional bias resistors which lower the input impedance and hence increase the loading to the previous stage.
• The power gain of a common emitter (CE) amplifier is higher than the power gain of a common collector (CC) amplifier or a common base (CB) amplifier

• Common collector configuration, also known as emitter follower provides high input impedance and low output impedance. So they are used for the purpose of impedance matching.
• In common collector configuration, the collector terminal is common to both input and output terminals. The current gain in the common-collector configuration is therefore the ratio of the emitter current to the base current.
• Since the emitter current is very high as compared to the base current, we get current amplification.
• It provides a voltage gain of less than unity.

Important Differences between different transistor configuration is as shown:

• The input impedance is high in the common collector because this is calculated by the Beta (gain) of the transistor, multiplied by the emitter resistance, whereas the current gain is due to the output impedance being inversely proportional to the current gain of the transistor in parallel to Re
• Common collector configuration, also known as emitter follower provides high input impedance and low output impedance. So they are used for the purpose of impedance matching.
• In common collector configuration, the collector terminal is common to both input and output terminals. The current gain in the common-collector configuration is therefore the ratio of the emitter current to the base current. Since the emitter current is very high as compared to the base current, we get current amplification. It provides a voltage gain of less than unity.

common collector configuration has low voltage gain and high current gain. The power gain of the common collector amplifier is medium. so option 4 is wrong

All the configurations are used in different circuits based on their applications:

The phase shift between the input and output of an emitter follower is 0º.
Emitter follower:

• The Emitter-follower circuit is also known as a common collector configuration.
• It is called the emitter follower configuration because the emitter voltage follows the base voltage.
• It is mostly used as a voltage buffer.
• The small-signal model & hybrid model is shown below:

The phase shift between the input and output of an emitter follower is 0º.
Emitter follower:

• The Emitter-follower circuit is also known as a common collector configuration.
• It is called the emitter follower configuration because the emitter voltage follows the base voltage.
• It is mostly used as a voltage buffer.
• The small-signal model & hybrid model is shown below:

Buffer:

• A Buffer is an op-amp circuit whose output voltage straight away follows the input voltage. i.e. output voltage equivalent to the input voltage.
• The Op-amp circuit does not provide any amplification thus, its voltage gain is unity.
• The voltage follower is used as a buffer amplifier, isolation amplifier, unity gain amplifier as the output follows the input.
• The voltage follower provides no alternation or amplification but only buffering.

Non-Inverting Buffer:
1. The buffer is a single-input device that has a gain of 1and provides the input at the output.
2. It has value for impedance matching and for isolation of the input and output.

Inverting Buffer:
1. The inverting buffer is a single-input device that produces the state opposite the input.
2. If the input is high, the output is low and vice versa.

Hence option (2) is the correct answer.
Characteristics:

• High input impedance
• Low output impedance
• Current Gain & power gain high
• Voltage gain unity

Common Collector configuration is also known as voltage buffer and emitter follower as it has unity voltage gain.

• CB configuration: Low Input impedance and High output impedance
• CC configuration: (Emitter follower): High Input impedance and low output impedance
• CE configuration: Moderate Input impedance and Moderate output impedance

• Common collector configuration, also known as emitter follower provides high input impedance and low output impedance. So they are used for the purpose of impedance matching.
• In common collector configuration, the collector terminal is common to both input and output terminals.

Important Differences between different transistor configuration is as shown: