A difference amplifier, also known as a differential amplifier, is an electronic circuit designed to amplify the voltage difference between two input signals while rejecting any common-mode voltage. In other words, it amplifies the voltage that exists between its two input terminals while minimizing the influence of any voltage that is present on both input terminals.
The primary purpose of a difference amplifier is to extract the useful information contained in the voltage difference between two signals, while eliminating or minimizing any unwanted noise or interference that might be common to both signals. This makes it particularly useful in scenarios where the signal of interest is relatively weak and buried within a larger common-mode voltage or noise component.
The basic configuration of a difference amplifier typically consists of two input terminals, each connected to an input signal, and an output terminal that provides the amplified voltage difference as the output signal. The circuit may utilize operational amplifiers (op-amps) to achieve the desired amplification and rejection of common-mode signals.
Use cases of difference amplifiers include:
Signal Conditioning: In sensor applications, where small signals from sensors (e.g., temperature, pressure, strain) need to be amplified and accurately extracted from background noise or common-mode signals.
Instrumentation Amplification: In scientific and engineering instrumentation, where accurate measurements are required. Difference amplifiers help amplify the difference in sensor readings while rejecting noise.
Biomedical Applications: In electrocardiogram (ECG) or electromyogram (EMG) measurements, where the desired bioelectric signals are small compared to the common-mode noise caused by muscle activity or other interference.
Audio Signal Processing: In audio equipment, to amplify the difference between stereo signals while canceling out any common-mode noise, resulting in clearer audio output.
Communication Systems: In differential signaling, where data is transmitted using the voltage difference between two wires (e.g., USB, Ethernet). Difference amplifiers help in decoding the transmitted data.
Bridge Circuits: In strain gauge bridges and other similar applications, where tiny changes in resistance need to be measured accurately by amplifying the voltage difference across the bridge.
Overall, the difference amplifier's ability to amplify the meaningful signal component while rejecting unwanted common-mode noise makes it a versatile circuit for a wide range of applications requiring accurate signal extraction and noise rejection.