Common Base Amplifier Circuit Working And Its Applications

An Amplifier circuit is used to increase the strength of the signal. The amplifier circuit uses the power supply to increase the signal strength. The amplification provided by the amplifier circuit is measured in terms of Gain of an amplifier. The gain of the amplifier is the ratio of output to input, which is always greater than one. Amplification does not alter frequency and waveform shape. In this article, we discuss on Common Base Amplifier circuit.

Gain of the Amplifier (A) = Output/(Input)


Below illustration gives the amplifier symbol.

Symbol of Amplifier
Symbol of Amplifier

Amplifier Module

Amplifier Module
Amplifier Module

The ideal amplifier module has three important properties, namely, input impedance (Rin), output impedance (Rout) and of course amplification called as Gain(A). The amplifier module explains the general system of amplification with input and output signal. The impedance Rin increases the signal strength at gain A to produce the desired signal strength. Rin should be infinite and Rout should be zero.

Types of Amplifiers

The below table explains the configuration, classification, and frequency of operation for different signals.

Type of Signal Configuration Classification Operational Frequency
Small Signals Common Emitter (CE) Class A Amplifier Direct Current (DC)
Large Signals Common Base (CB) Class B Amplifier Audio Frequency (AF)
Common Collector (CC) Class AB Amplifier Radio Frequency (RF)
Class C Amplifier VHF, UHF and SHF Frequencies

Different Amplifier Configurations

Transistors are used in amplifiers in three different configurations, namely,

  • Common Base (CB)
  • Common Collector (CC)
  • Common Emitter (CE).

The Common Emitter circuit is most widely used configuration. This circuit has grounded emitter. This circuit gives a medium level input impedance and output impedance. Voltage gain and current gain are medium, and the output reverses the input.

The Common collector circuit is widely used as a buffer. It is called as Emitter-follower. The emitter voltage follows that of the base. This gives a high input impedance and low output impedance. It has grounded collector.

The Common base circuit provides low input impedance and high output impedance. The base of the transistor in this configuration is grounded. Input and output are in phase.

Common Base Amplifier Circuit

NPN and PNP transistors are used in Amplifier circuits. Both NPN and PNP have input provided at the emitter of the transistor and the output is taken at the collector of the transistor.

Common Base Amplifier Configuration
Common Base Amplifier Configuration

The below diagram shows how common base amplifier circuit is implemented.

Common Base Amplifier Circuit
Common Base Amplifier Circuit

The biasing constraints are same, but the applications of the signals are different. In this circuit, care has to be taken such that correct impedance match is provided to the input signal.

Characteristics of Common Base Amplifier Circuit

The following are the characteristics of the Common Base amplifier circuit.

  • High voltage gain
  • Low current gain
  • Low power gain
  • Input and output phase relation is 0o
  • It has low input impedance
  • It has high output impedance


The common base amplifier circuit is used, where the low input impedance is required. The following are the applications of the common base amplifier circuit.

  • It is used in moving coil microphones Preamplifiers.
  • It is used in UHF and VHF RF amplifiers.

Furthermore, any queries regarding this article or if you want to implement Electrical and Electronics projects for engineering students, please feel free to comment in the below section. Here is the question for you, what is the voltage gain of the common base amplifier?