A difference amplifier, also known as a differential amplifier, is an electronic circuit designed to amplify the difference between two input signals while rejecting any common-mode signals (signals that are present in both inputs with the same amplitude and phase). Its primary use is to amplify the voltage difference between two input signals, while minimizing the impact of any noise or interference that is common to both inputs.
The basic operation of a difference amplifier relies on the fact that it amplifies the voltage difference between its two input terminals (often referred to as the inverting input and the non-inverting input) and produces an output voltage proportional to this difference. The common-mode rejection ratio (CMRR) is a key parameter used to quantify the ability of a difference amplifier to reject common-mode signals. A higher CMRR value indicates better rejection of common-mode signals.
In the context of subtracting signals, a difference amplifier can be utilized to compute the voltage difference between two signals. One signal is usually applied to the inverting input terminal, and the other signal is applied to the non-inverting input terminal. The output voltage of the difference amplifier will then be proportional to the difference between these input voltages.
For example, let's say you have two sensors measuring temperature: one in a controlled environment and another in an experimental setup. You want to measure the temperature difference between the controlled environment and the experimental setup, while minimizing the impact of any common-mode noise, such as electrical interference or temperature fluctuations in the surroundings. By connecting the sensors to a difference amplifier, you can subtract the temperature signals and obtain a cleaner output that primarily reflects the temperature difference between the two environments, disregarding common-mode noise.
Overall, a difference amplifier is a fundamental circuit component in various applications where accurate signal subtraction is necessary, such as instrumentation, measurement systems, audio equipment, and biomedical devices. It allows for precise extraction of the difference between two input signals while minimizing the influence of unwanted common-mode components.