Explain the concept of common-base configuration in transistor amplifiers.
1 Answer
The common-base configuration is one of the three basic transistor amplifier configurations, the other two being common-emitter and common-collector. In the common-base configuration, a transistor is connected such that the base terminal is the common terminal between the input and output sides of the circuit. This means that the input is applied to the emitter terminal, and the output is taken from the collector terminal.
Key characteristics and features of the common-base configuration include:
Input and Output Relationships: In this configuration, the input current is the emitter current (Ie), and the output current is the collector current (Ic). The input voltage is applied across the emitter-base junction, while the output voltage is measured across the collector-base junction.
Current Amplification: The common-base configuration offers current amplification. A small change in the input current (Ie) leads to a larger change in the output current (Ic). However, voltage gain in this configuration is less than in the common-emitter configuration.
Phase Relationship: The phase relationship between the input and output voltages is inverted. This means that when the input voltage increases, the output voltage decreases, and vice versa.
Low Input Impedance, High Output Impedance: The input impedance of the common-base amplifier is relatively low, which means it can handle low impedance sources. The output impedance, on the other hand, is high, making it suitable for driving high impedance loads.
Voltage Gain: The voltage gain in the common-base configuration is typically less than 1. It is defined as the ratio of the change in output voltage (ΔVc) to the change in input voltage (ΔVe), and is given by the formula: Voltage Gain (Av) = -ΔVc / ΔVe.
Application: Common-base amplifiers are not as commonly used for voltage amplification as common-emitter amplifiers due to their lower voltage gain. However, they find applications in RF (Radio Frequency) amplification and impedance matching due to their unique characteristics.
In summary, the common-base configuration provides current amplification with an inverted phase relationship between input and output voltages. It has a lower voltage gain compared to the common-emitter configuration but is useful in specific applications where impedance matching and RF amplification are important.
Key characteristics and features of the common-base configuration include:
Input and Output Relationships: In this configuration, the input current is the emitter current (Ie), and the output current is the collector current (Ic). The input voltage is applied across the emitter-base junction, while the output voltage is measured across the collector-base junction.
Current Amplification: The common-base configuration offers current amplification. A small change in the input current (Ie) leads to a larger change in the output current (Ic). However, voltage gain in this configuration is less than in the common-emitter configuration.
Phase Relationship: The phase relationship between the input and output voltages is inverted. This means that when the input voltage increases, the output voltage decreases, and vice versa.
Low Input Impedance, High Output Impedance: The input impedance of the common-base amplifier is relatively low, which means it can handle low impedance sources. The output impedance, on the other hand, is high, making it suitable for driving high impedance loads.
Voltage Gain: The voltage gain in the common-base configuration is typically less than 1. It is defined as the ratio of the change in output voltage (ΔVc) to the change in input voltage (ΔVe), and is given by the formula: Voltage Gain (Av) = -ΔVc / ΔVe.
Application: Common-base amplifiers are not as commonly used for voltage amplification as common-emitter amplifiers due to their lower voltage gain. However, they find applications in RF (Radio Frequency) amplification and impedance matching due to their unique characteristics.
In summary, the common-base configuration provides current amplification with an inverted phase relationship between input and output voltages. It has a lower voltage gain compared to the common-emitter configuration but is useful in specific applications where impedance matching and RF amplification are important.