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 any common-mode signals that are present in both inputs. Its primary purpose is to amplify the "difference" between the voltages of two input signals while attenuating or rejecting any common voltage components that appear in both signals. This makes it particularly useful in applications where you want to measure or amplify the difference between two signals while ignoring any common noise or interference that might affect both signals equally.
The basic concept of a difference amplifier involves using multiple amplifying components, such as operational amplifiers (op-amps), transistors, or integrated circuits, to achieve the desired amplification and subtraction of the input signals.
Here's a simplified example of a difference amplifier circuit using an operational amplifier (op-amp):
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V1
│
│
──────┼──────
+ │ │
│ │ │
│ ▼ ▼
│ R1 R2
│ ▲ │
│ │ │
──────┼──────
│
│
V2
In this circuit:
V1 and V2 are the input voltages.
R1 and R2 are resistors.
The op-amp amplifies the voltage difference (V1 - V2) and provides the output.
The amplified output, Vo, can be calculated as:
Vo = (R2 / R1) * (V1 - V2)
The use of a difference amplifier becomes especially significant when subtracting signals. Imagine you have two signals, A and B, and you want to measure the difference between them while ignoring any common noise or interference. By connecting A to one input and B to the other input of the difference amplifier, the circuit will output the amplified difference between A and B, effectively subtracting one from the other.
Applications of difference amplifier circuits include instrumentation, audio processing, signal conditioning, and data acquisition systems, where accurate measurement of signal differences is crucial while minimizing the impact of common noise or disturbances.