Define common-base configuration in bipolar transistors.
1 Answer
In electronics, a common-base configuration is one of the three basic transistor amplifier configurations, the other two being common-emitter and common-collector. Transistors are semiconductor devices that can amplify electrical signals. The common-base configuration is designed around a bipolar junction transistor (BJT) and is characterized by the way the input and output signals are connected to the transistor's terminals.
In a common-base configuration:
Emitter Terminal (E): The emitter terminal is the input terminal, where the input signal is applied. It is also the terminal through which the emitter current flows into the transistor.
Base Terminal (B): The base terminal is the common terminal between the input and output sides of the configuration. It is the terminal that controls the transistor's operation. The base current controls the collector current.
Collector Terminal (C): The collector terminal is the output terminal, where the amplified output signal is taken. The collector current flows out of the transistor through this terminal.
Key characteristics of the common-base configuration:
Voltage Gain: The common-base configuration provides voltage gain, which means it can amplify input voltage signals. The voltage gain is typically lower than that of the common-emitter configuration, but it has a wider bandwidth.
Current Gain: The common-base configuration has a current gain, which is the ratio of the change in collector current to the change in base current. However, the current gain is usually less than unity (less than 1), making this configuration less suitable for current amplification.
Phase Relationship: The output signal in a common-base configuration is 180 degrees out of phase with the input signal. This phase inversion can be useful in specific applications.
Input and Output Impedances: The input impedance of the common-base configuration is relatively low, while the output impedance is relatively high. This can make it useful for impedance matching between stages of a larger circuit.
The common-base configuration is less commonly used than the common-emitter and common-collector configurations due to its lower gain and unique characteristics. It is often employed in high-frequency amplifier circuits and applications where phase inversion is required.
In a common-base configuration:
Emitter Terminal (E): The emitter terminal is the input terminal, where the input signal is applied. It is also the terminal through which the emitter current flows into the transistor.
Base Terminal (B): The base terminal is the common terminal between the input and output sides of the configuration. It is the terminal that controls the transistor's operation. The base current controls the collector current.
Collector Terminal (C): The collector terminal is the output terminal, where the amplified output signal is taken. The collector current flows out of the transistor through this terminal.
Key characteristics of the common-base configuration:
Voltage Gain: The common-base configuration provides voltage gain, which means it can amplify input voltage signals. The voltage gain is typically lower than that of the common-emitter configuration, but it has a wider bandwidth.
Current Gain: The common-base configuration has a current gain, which is the ratio of the change in collector current to the change in base current. However, the current gain is usually less than unity (less than 1), making this configuration less suitable for current amplification.
Phase Relationship: The output signal in a common-base configuration is 180 degrees out of phase with the input signal. This phase inversion can be useful in specific applications.
Input and Output Impedances: The input impedance of the common-base configuration is relatively low, while the output impedance is relatively high. This can make it useful for impedance matching between stages of a larger circuit.
The common-base configuration is less commonly used than the common-emitter and common-collector configurations due to its lower gain and unique characteristics. It is often employed in high-frequency amplifier circuits and applications where phase inversion is required.