A difference amplifier, also known as a differential amplifier, is a fundamental electronic circuit designed to amplify the difference between two input voltages while rejecting common-mode signals. Its primary purpose is to extract the useful signal (the difference) from two input signals while eliminating any noise or interference that may be present in both signals simultaneously.
The difference amplifier is particularly useful in various applications, including:
Signal Amplification: In some cases, the voltage levels of the input signals may be too low for further processing. The difference amplifier amplifies the voltage difference, allowing the signal to reach a suitable level for subsequent stages of the circuit.
Noise Rejection: When signals are transmitted over long distances or picked up from external sources, they can be contaminated by unwanted noise or interference. Since the difference amplifier only amplifies the difference between the inputs, any noise that is common to both inputs (common-mode noise) is canceled out. This greatly enhances the signal-to-noise ratio, making the desired signal more distinguishable.
Instrumentation Amplification: In measurement and sensing applications, where the difference in voltage levels represents the physical parameter being measured (e.g., temperature, pressure, strain), a difference amplifier can be used to amplify and accurately measure this difference.
Balanced Communication Systems: In communication systems, such as differential signaling used in modern high-speed data transmission (e.g., USB, Ethernet), difference amplifiers help reduce noise and increase noise immunity.
The basic configuration of a difference amplifier consists of two inputs (inverting and non-inverting) and an output. The output voltage is proportional to the difference between the two input voltages, as well as the gain set by external resistors in the circuit. It is represented by the equation:
Vout = Gain × (V2 - V1)
where Vout is the output voltage, V1 is the voltage at the inverting input, V2 is the voltage at the non-inverting input, and Gain is the amplification factor determined by the circuit's resistors.
Overall, the difference amplifier is a versatile circuit used in a wide range of applications where the extraction of the difference between two input signals is crucial, and common-mode noise rejection is necessary.