A difference amplifier circuit, also known as a differential amplifier, is a fundamental electronic circuit designed to measure the voltage difference between two input signals. Its primary purpose is to amplify the voltage difference while rejecting or minimizing any common-mode voltage that appears on both inputs simultaneously. This makes it particularly useful in applications where the actual signal of interest is the voltage difference between two signals, rather than their individual magnitudes.
Here's a breakdown of the key features and purposes of a difference amplifier circuit:
Voltage Difference Amplification: The primary function of a difference amplifier is to amplify the voltage difference between its two input terminals. This amplified output voltage can be used to extract the relevant information from the input signals, especially when the signal of interest is the difference between the two input voltages.
Common-Mode Rejection: Common-mode voltage refers to any voltage that appears equally on both input terminals of the amplifier. This can be caused by external noise, interference, or any other factors affecting both inputs equally. One of the key advantages of a difference amplifier is its ability to reject or cancel out common-mode voltages. The differential gain amplifies only the voltage difference between the inputs, while any common-mode voltage gets suppressed in the output.
Precision Signal Acquisition: Difference amplifiers are commonly used in measurement and instrumentation systems where accurate and precise acquisition of differential signals is essential. For example, in medical devices like ECG (electrocardiogram) machines, the voltage difference between electrodes placed on different parts of the body needs to be measured accurately.
Noise Reduction: By rejecting common-mode voltages and focusing only on the differential voltage, a difference amplifier helps reduce the impact of noise and interference on the measured signal. This is particularly important in sensitive applications where maintaining signal integrity is crucial.
Operational Amplifier Configuration: Difference amplifiers are often built using operational amplifiers (op-amps) as the core active components. Op-amps are versatile and can be configured to provide high gain, high input impedance, and low output impedance, which are desirable qualities in difference amplifier applications.
Instrumentation Amplifiers: In some cases, a difference amplifier is combined with additional amplifier stages to create an instrumentation amplifier. An instrumentation amplifier provides even higher common-mode rejection and differential gain while offering better overall performance in terms of accuracy and noise immunity.
In summary, the purpose of a difference amplifier circuit is to amplify the voltage difference between two input signals while effectively rejecting any common-mode voltage that might be present. This makes it a valuable tool in various applications such as measurement, signal processing, medical equipment, and any situation where accurate extraction of differential signals is essential.