A summing amplifier, also known as an inverting summing amplifier, is an electronic circuit configuration commonly used in analog signal processing. Its primary function is to combine multiple input voltages (analog signals) and produce an output voltage that is a weighted sum of those inputs. The summing amplifier is based on the operational amplifier (op-amp) and is typically designed to perform mathematical operations like addition and subtraction of input signals.
The basic configuration of a summing amplifier consists of an op-amp with multiple input resistors connected to its inverting (-) input terminal. Each input signal is applied through a separate input resistor, and these input resistors determine the scaling or weighting factor for each input.
The general formula for the output voltage (Vout) of a summing amplifier is:
Vout = - (Rf / Rin1) * Vin1 - (Rf / Rin2) * Vin2 - ... - (Rf / Rinn) * Vinn
Where:
Vout is the output voltage.
Rf is the feedback resistor connected between the op-amp's output and inverting input.
Rin1, Rin2, ..., Rinn are the input resistors associated with each input voltage Vin1, Vin2, ..., Vinn.
Vin1, Vin2, ..., Vinn are the input voltages.
By properly selecting the values of the feedback resistor and the input resistors, you can control the contribution of each input signal to the output voltage. This allows you to create custom combinations of input signals according to the desired mathematical relationship. For example, you can use a summing amplifier to:
Add or subtract multiple input signals.
Implement weighted summing of signals, where some inputs have a stronger influence on the output than others.
Create voltage offsets or references by connecting a fixed voltage source to one of the input resistors.
The ability to combine inputs in various ways makes the summing amplifier a versatile component in analog signal processing circuits, commonly used in applications like audio mixers, instrumentation amplifiers, and control systems.