A difference amplifier, also known as a differential amplifier, is an electronic circuit that amplifies the difference between two input voltages while rejecting any common-mode signals that are present on both inputs. The primary purpose of a difference amplifier is to amplify the voltage difference between the two inputs while rejecting noise and interference that affects both inputs equally.
The basic configuration of a difference amplifier typically consists of two input terminals, labeled as Vā and Vā, and two output terminals. The output voltage is proportional to the difference between the voltages applied to the input terminals. The equation for the output voltage (V_out) of a difference amplifier is as follows:
V_out = (Vā - Vā) * A_d
Where:
V_out is the output voltage.
Vā is the voltage applied to the first input terminal.
Vā is the voltage applied to the second input terminal.
A_d is the differential gain, which represents the amplification factor for the voltage difference between Vā and Vā.
The differential gain (A_d) is a key parameter of the difference amplifier and determines the level of amplification applied to the voltage difference between the inputs. The common-mode rejection ratio (CMRR) is another essential parameter that quantifies how well the difference amplifier suppresses common-mode signals.
Use of a Difference Amplifier:
Difference amplifiers are widely used in various applications, including:
Instrumentation: They are used in measurement systems to amplify small voltage differences from sensors and transducers, ensuring accurate readings in noisy environments.
Audio Processing: In audio circuits, difference amplifiers are used for balanced audio signal transmission, which helps reduce noise and interference.
Signal Conditioning: They play a vital role in conditioning signals for further processing in analog-to-digital converters (ADCs) and other electronic circuits.
Communication Systems: Difference amplifiers are used in communication systems for receiving and transmitting signals while rejecting common-mode noise.
Biomedical Applications: In biomedical devices, difference amplifiers are used to amplify weak biopotentials from electrodes attached to the body, allowing for precise measurement of physiological signals.
Overall, the difference amplifier's ability to amplify the voltage difference between inputs while rejecting common-mode noise makes it a versatile and essential component in various electronic circuits and systems.