What is a common-emitter amplifier?
1 Answer
A common-emitter amplifier is a type of electronic amplifier used to amplify small AC signals or voltages. It is one of the most widely used configurations for bipolar junction transistor (BJT) amplifiers. The common-emitter configuration provides a relatively high voltage gain and is commonly used in audio and radio frequency (RF) applications.
The term "common-emitter" refers to the transistor's emitter terminal being connected to a common ground or reference point in the circuit. In this configuration, the input signal is applied between the base and emitter terminals, and the output is taken from the collector and emitter terminals. The collector is usually connected to a supply voltage through a resistor known as the collector load resistor.
The key characteristics of a common-emitter amplifier are as follows:
Voltage amplification: The input voltage applied between the base and emitter causes a proportional current to flow through the base-emitter junction. This current is amplified by the transistor, resulting in a larger voltage variation across the collector load resistor, producing an amplified output voltage.
Inverting amplifier: The common-emitter amplifier is an inverting amplifier, meaning that the output signal is 180 degrees out of phase with the input signal. When the input signal increases, the output signal decreases, and vice versa.
Moderate input impedance and relatively high output impedance: The input impedance is determined primarily by the base-emitter junction, while the output impedance is influenced by the collector load resistor.
Current gain: The common-emitter configuration exhibits current gain (β), which is the ratio of collector current (Ic) to base current (Ib). The current gain is an essential parameter to consider when designing and analyzing these amplifiers.
The common-emitter amplifier is widely used due to its versatility and ability to provide relatively high voltage gain, making it suitable for various applications such as audio amplification, signal conditioning, and interfacing between different stages of a circuit.
However, it also has some drawbacks, such as its sensitivity to temperature variations and its relatively low input impedance compared to other configurations like common-base or common-collector amplifiers. Despite these limitations, it remains a fundamental and commonly used circuit in electronics.
The term "common-emitter" refers to the transistor's emitter terminal being connected to a common ground or reference point in the circuit. In this configuration, the input signal is applied between the base and emitter terminals, and the output is taken from the collector and emitter terminals. The collector is usually connected to a supply voltage through a resistor known as the collector load resistor.
The key characteristics of a common-emitter amplifier are as follows:
Voltage amplification: The input voltage applied between the base and emitter causes a proportional current to flow through the base-emitter junction. This current is amplified by the transistor, resulting in a larger voltage variation across the collector load resistor, producing an amplified output voltage.
Inverting amplifier: The common-emitter amplifier is an inverting amplifier, meaning that the output signal is 180 degrees out of phase with the input signal. When the input signal increases, the output signal decreases, and vice versa.
Moderate input impedance and relatively high output impedance: The input impedance is determined primarily by the base-emitter junction, while the output impedance is influenced by the collector load resistor.
Current gain: The common-emitter configuration exhibits current gain (β), which is the ratio of collector current (Ic) to base current (Ib). The current gain is an essential parameter to consider when designing and analyzing these amplifiers.
The common-emitter amplifier is widely used due to its versatility and ability to provide relatively high voltage gain, making it suitable for various applications such as audio amplification, signal conditioning, and interfacing between different stages of a circuit.
However, it also has some drawbacks, such as its sensitivity to temperature variations and its relatively low input impedance compared to other configurations like common-base or common-collector amplifiers. Despite these limitations, it remains a fundamental and commonly used circuit in electronics.