A difference amplifier circuit, also known as a differential amplifier or subtractor circuit, is an electronic circuit designed to amplify the difference between two input signals while rejecting common-mode signals that are present on both inputs. The primary purpose of a difference amplifier is to extract the difference between two input voltages and amplify it, while canceling out any unwanted common components.
The basic configuration of a difference amplifier involves using operational amplifiers (op-amps) and resistors. An op-amp is a high-gain voltage amplifier with two input terminals (inverting and non-inverting) and an output terminal. The inputs of the op-amp are connected to the input signals, and the output is taken from the output terminal of the op-amp.
In a simple difference amplifier circuit, there are two input signals, usually referred to as
1
V
1
and
2
V
2
, and two resistors,
1
R
1
and
2
R
2
, which form a voltage divider network. The circuit diagram can be represented as:
scss
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+Vin (V1) +Vcc
| |
R1 R2
| |
+--------(O)-----------+---- Vout
| |
-Vin (V2) GND
In this configuration, the op-amp amplifies the voltage difference
diff
=
1
−
2
V
diff
=V
1
−V
2
across the input terminals. The output voltage (
out
V
out
) is given by:
out
=
2
1
⋅
(
1
−
2
)
V
out
=
R
1
R
2
⋅(V
1
−V
2
)
The gain of the difference amplifier can be adjusted by selecting appropriate resistor values for
1
R
1
and
2
R
2
.
Usage in subtracting signals:
The primary application of a difference amplifier is to subtract one voltage signal from another. This is particularly useful in scenarios where you have a desired signal riding on a common-mode noise or interference signal. By using a difference amplifier, you can effectively remove or attenuate the common-mode signal while retaining the difference signal of interest.
For example, in instrumentation and sensor circuits, where a sensor signal might be affected by noise or offset, a difference amplifier can help extract the actual measurement signal by subtracting out the noise or offset voltage.
In audio applications, difference amplifiers can be used to remove common-mode noise, such as ground loops, from audio signals to improve audio quality.
In summary, a difference amplifier circuit is a versatile tool for subtracting signals, allowing you to obtain the meaningful difference between two input voltages while rejecting common-mode interference.