A difference amplifier, also known as a differential amplifier, is an electronic circuit that amplifies the voltage difference between two input signals while rejecting any common-mode signals that appear on both inputs. The main purpose of a difference amplifier is to subtract two input signals and amplify the resulting difference.
The general configuration of a difference amplifier includes two input terminals (Vā and Vā) and two output terminals (Vo and ground). The output voltage (Vo) is proportional to the voltage difference between the two inputs (Vā - Vā) and is expressed as follows:
Vo = A(Vā - Vā)
Where:
Vo is the output voltage,
Vā is the voltage at the non-inverting input terminal,
Vā is the voltage at the inverting input terminal, and
A is the voltage gain of the amplifier.
Ideally, the difference amplifier amplifies only the voltage difference between Vā and Vā while rejecting any common-mode voltage that is present at both inputs. Common-mode voltage refers to any signal that is present on both inputs with the same amplitude and phase. By rejecting the common-mode signal, the difference amplifier provides better noise immunity and can accurately extract the difference between the two input signals.
The difference amplifier finds numerous applications, with one of its primary uses being signal subtraction. For instance, in instrumentation and control systems, the difference amplifier is used to measure the difference between two sensor outputs. If two sensors are measuring the same physical quantity (e.g., temperature, pressure) but are subjected to different environmental conditions, the difference amplifier can help identify the actual change in the measured quantity by subtracting the common-mode noise or interference. This results in a more precise and accurate measurement.
Overall, the difference amplifier is a crucial component in various circuits where the subtraction of signals is required while maintaining high common-mode rejection and accuracy.