Subject: Logic Design

Topic: Biasing of BJT

Difficulty: Hard

Differential Amplifier

The electronic amplifier used for amplifying the difference between two input signals can be called as a differential amplifier. In general, these differential amplifiers consist of two terminals namely inverting terminal and non-inverting terminal. These inverting and non-inverting terminals are represented with – and + respectively.

Differential Amplifier Circuit

The differential amplifier can be considered as an analog circuit which consists of two inputs and one output. The differential amplifier circuit can be represented as shown in the figure below.

Differential Amplifier

The output voltage of a differential amplifier is proportional to the difference between the two input voltages. This can be represented in equation form as follows:

$V_{out} = A (V^+_{in} - V^-_{in})$

Where, A= gain of the amplifier.

The differential amplifier circuit using transistors can be designed as shown in the figure below which consists of two transistors T1 and T2. These transistors and resistors are connected as shown in the circuit diagram.