A summing amplifier, also known as an op-amp (operational amplifier) adder or an inverting adder, is a type of electronic circuit that combines multiple input signals and produces an output voltage that is the sum of those inputs. It is a fundamental building block in analog electronic circuits and is widely used in various applications, such as audio mixing, signal processing, 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. Each input signal is connected to a separate input resistor, and the other end of all the resistors is connected to a common junction point. The non-inverting (+) input terminal of the op-amp is typically connected to a virtual ground, which means the voltage at this terminal is considered to be zero.
Here's a simplified representation of a summing amplifier with two input signals (V1 and V2):
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+Vcc
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Rf
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Vin1 ---/\/\/\-----> Output (Vout)
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Vin2 ---/ |
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---- |
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GND GND
The output voltage (Vout) of the summing amplifier is given by the formula:
Vout = - ( Rf / Rin1 ) * Vin1 - ( Rf / Rin2 ) * Vin2
where:
Vout is the output voltage of the summing amplifier.
Rf is the feedback resistor, connected between the output and the inverting input terminal of the op-amp.
Rin1 and Rin2 are the input resistors for the respective input signals Vin1 and Vin2.
The negative sign in the formula indicates that the output voltage is an inverted sum of the input voltages. This means that if Vin1 and Vin2 are both positive, the output voltage will be negative, and vice versa. The gain of each input (Rf / Rin) determines the contribution of that input to the output. By adjusting the values of the input resistors, you can set the relative weights of the input signals, enabling you to sum them in various proportions.
Summing amplifiers are not limited to two inputs; they can be designed to handle more inputs by adding more input resistors and appropriately calculating the feedback resistor and resistor ratios for each input.
In summary, a summing amplifier can combine multiple input signals and produce an output voltage that represents their sum, with each input signal weighted by the ratio of its input resistor to the feedback resistor.