A summing amplifier, also known as an op-amp (operational amplifier) summer, is an electronic circuit that combines multiple input signals and produces an output voltage that is proportional to the sum of these input voltages. It is a common application of operational amplifiers used in various electronic systems, including audio mixers, signal processing circuits, and control systems.
The basic configuration of a summing amplifier consists of an operational amplifier with multiple input resistors connected to its inverting input terminal (usually marked with a negative sign "-"). The non-inverting input terminal is typically connected to a reference voltage (ground or any other desired reference level).
The general circuit diagram of a summing amplifier with two inputs (V1 and V2) looks like this:
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V1 --- R1 ---
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V2 --- R2 ---|--- Output (Vout)
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... ... ...
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Vn --- Rn ---
Here's how it works:
Inverting Input: The inverting input terminal (-) of the operational amplifier is a virtual ground in this configuration. It means that the voltage at the inverting input is assumed to be the same as the non-inverting input voltage (which is usually the reference voltage).
Input Resistors: Each input voltage (V1, V2, ..., Vn) is connected to the inverting input through an input resistor (R1, R2, ..., Rn). The resistors serve as a current-to-voltage converter, converting the input currents into voltages.
Superposition Principle: According to the superposition principle, the output voltage (Vout) is the sum of the individual contributions from each input. The output voltage can be calculated using the following formula:
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Vout = - (V1/R1 + V2/R2 + ... + Vn/Rn)
The negative sign appears in the formula because the output of the operational amplifier is inverted in a typical configuration. If you need a non-inverting summing amplifier, you can rearrange the inputs and use a non-inverting amplifier configuration.
By adjusting the values of the resistors, you can control the gain of each input, allowing you to scale the contributions of individual input signals in the final output. This makes the summing amplifier a versatile circuit for combining multiple signals in various applications.