A difference amplifier, also known as a subtractor circuit, is an electronic circuit used to compute the difference between two input voltage signals. It performs subtraction by amplifying the voltage difference between its two input terminals while rejecting common-mode signals (signals that are present on both inputs with the same magnitude and phase).
The basic configuration of a difference amplifier circuit consists of an operational amplifier (op-amp) with two input resistors, labeled as R1 and R2, connected to the inverting (-) input terminal, and two input voltage signals, Vā and Vā, connected to the non-inverting (+) input terminal and the inverting input terminal, respectively. The output voltage, Vout, is proportional to the voltage difference between Vā and Vā, scaled by the resistor values:
Vout = - (R2 / R1) * (Vā - Vā)
In this configuration, the output voltage is the amplified difference between the two input voltages, and the minus sign arises from the inverting nature of the op-amp configuration. The resistor values R1 and R2 determine the gain of the amplifier.
Uses of a difference amplifier (subtractor) circuit:
Signal Processing: Difference amplifiers are commonly used in signal processing applications to extract the difference between two input signals. This is useful in scenarios where you want to eliminate a common-mode signal (such as noise or interference) that is present on both input signals.
Instrumentation: Difference amplifiers play a crucial role in instrumentation circuits, such as bridge circuits used in sensors and transducers. For instance, in a strain gauge bridge, a difference amplifier can be used to amplify and extract the small voltage difference caused by strain on the gauge.
Biomedical Applications: In biomedical devices, difference amplifiers can be used to measure bioelectric signals, such as the difference in potential between two points on the body. This is common in electrocardiogram (ECG) and electroencephalogram (EEG) measurements.
Audio and Music: Difference amplifiers can be used in audio applications, such as audio mixers, where you might need to subtract or mix different audio signals.
Voltage Offset Compensation: Difference amplifiers are also used to compensate for voltage offsets in certain circuits. By amplifying the difference between two signals, the effect of a constant voltage offset can be minimized.
Communication Systems: In some communication systems, difference amplifiers can be used to remove common-mode noise from signals.
Overall, difference amplifiers are versatile circuits that find applications in various fields where precise subtraction and common-mode rejection are required.