Define common emitter configuration in transistor amplifiers.
1 Answer
The common emitter configuration is one of the basic and widely used configurations in bipolar junction transistor (BJT) amplifiers. It is commonly employed to amplify weak AC signals, such as audio or radio frequency signals, and provides both voltage and current amplification. In this configuration, the emitter terminal of the BJT is the common terminal for both the input and output signals.
Here's a breakdown of the key characteristics and operation of the common emitter configuration:
BJT Type: NPN or PNP transistor can be used, but for illustration purposes, let's consider an NPN transistor.
Biasing: The base-emitter junction is forward-biased, while the base-collector junction is reverse-biased. This ensures the transistor operates in the active region, where it can amplify signals.
Input Signal: The input AC signal is coupled to the base-emitter junction through a coupling capacitor (Cin) to block the DC bias. This prevents the input DC bias from affecting the AC signal.
Output Signal: The output is taken from the collector-emitter junction through a load resistor (Rc). The load resistor converts the collector current variations into an output voltage signal.
Amplification: As the input AC signal changes the base current, it leads to corresponding changes in the collector current, which results in voltage variations across the load resistor. This voltage variation amplifies the input signal.
Phase Relationship: The common emitter configuration provides a 180-degree phase shift between the input and output signals. This means that the output signal is inverted relative to the input signal.
Voltage Gain: The common emitter configuration typically offers moderate to high voltage gain. The voltage gain (Av) is given by the ratio of the change in output voltage (ΔVout) to the change in input voltage (ΔVin): Av = -ΔVout / ΔVin.
Current Gain: The configuration also provides a significant current gain. The current gain (β) of the transistor refers to the ratio of collector current (Ic) to base current (Ib).
Applications: Common emitter amplifiers find applications in various electronic devices, including audio amplifiers, RF amplifiers, and signal processing circuits.
Drawbacks: While the common emitter configuration provides amplification, it introduces signal inversion, and the output is taken with respect to the supply voltage, making it more sensitive to changes in power supply voltage. It also has limited input and output impedance matching, which can affect its overall performance.
In summary, the common emitter configuration is a fundamental building block in transistor amplifier design, offering voltage and current amplification with an inverted output and moderate to high gain.
Here's a breakdown of the key characteristics and operation of the common emitter configuration:
BJT Type: NPN or PNP transistor can be used, but for illustration purposes, let's consider an NPN transistor.
Biasing: The base-emitter junction is forward-biased, while the base-collector junction is reverse-biased. This ensures the transistor operates in the active region, where it can amplify signals.
Input Signal: The input AC signal is coupled to the base-emitter junction through a coupling capacitor (Cin) to block the DC bias. This prevents the input DC bias from affecting the AC signal.
Output Signal: The output is taken from the collector-emitter junction through a load resistor (Rc). The load resistor converts the collector current variations into an output voltage signal.
Amplification: As the input AC signal changes the base current, it leads to corresponding changes in the collector current, which results in voltage variations across the load resistor. This voltage variation amplifies the input signal.
Phase Relationship: The common emitter configuration provides a 180-degree phase shift between the input and output signals. This means that the output signal is inverted relative to the input signal.
Voltage Gain: The common emitter configuration typically offers moderate to high voltage gain. The voltage gain (Av) is given by the ratio of the change in output voltage (ΔVout) to the change in input voltage (ΔVin): Av = -ΔVout / ΔVin.
Current Gain: The configuration also provides a significant current gain. The current gain (β) of the transistor refers to the ratio of collector current (Ic) to base current (Ib).
Applications: Common emitter amplifiers find applications in various electronic devices, including audio amplifiers, RF amplifiers, and signal processing circuits.
Drawbacks: While the common emitter configuration provides amplification, it introduces signal inversion, and the output is taken with respect to the supply voltage, making it more sensitive to changes in power supply voltage. It also has limited input and output impedance matching, which can affect its overall performance.
In summary, the common emitter configuration is a fundamental building block in transistor amplifier design, offering voltage and current amplification with an inverted output and moderate to high gain.