A difference amplifier circuit, also known as a differential amplifier, is an electronic circuit designed to amplify the difference between two input signals while rejecting common-mode signals. Common-mode signals are those that appear equally on both inputs and are often unwanted noise or interference. The primary function of a difference amplifier is to provide a high gain to the difference between the two input signals while minimizing the amplification of the common-mode component.
Difference amplifiers are commonly used in various applications, including:
Signal Conditioning: In measurement and sensor applications, where small signals need to be accurately amplified, a difference amplifier can help extract the relevant signal from noise and interference.
Instrumentation Amplifiers: Difference amplifiers are a crucial part of instrumentation amplifier circuits, which are widely used in instrumentation and measurement systems to provide high input impedance, high gain, and good common-mode rejection.
Audio Amplification: In audio circuits, difference amplifiers can be used to amplify differential audio signals (e.g., balanced audio signals from microphones) while rejecting common-mode noise.
Communication Systems: In radio frequency (RF) and communication systems, difference amplifiers are used to amplify modulated signals while rejecting unwanted common-mode noise and interference.
Biomedical Applications: In medical electronics, difference amplifiers are employed in bioelectric signal measurement and processing, such as electrocardiography (ECG) and electromyography (EMG).
Control Systems: In control applications, difference amplifiers can be used for error amplification and feedback signal processing.
The key advantage of a difference amplifier is its ability to provide accurate amplification of the desired signal while rejecting unwanted noise and interference. This is especially important in scenarios where the signal of interest is relatively small compared to the surrounding noise. The common-mode rejection ratio (CMRR) is a parameter that quantifies how well a difference amplifier rejects common-mode signals, and higher CMRR values indicate better noise rejection.