A summing amplifier, also known as an op-amp (operational amplifier) summing circuit, is an electronic circuit used to combine multiple input signals and produce a single output signal that is the algebraic sum of all the inputs. It is a type of inverting amplifier that provides an inverted output relative to the input voltages.
The basic configuration of a summing amplifier consists of an operational amplifier (op-amp) with multiple input resistors connected to the inverting terminal (often labeled as the "-" input) of the op-amp. Each input signal is connected through a separate resistor, and the other ends of all resistors are joined together at a single point called the virtual summing point. The non-inverting terminal (often labeled as the "+" input) is typically connected to a reference voltage, such as ground.
The concept behind the summing amplifier is based on the principle that the current into the op-amp's inverting input is nearly zero, which means that the virtual summing point is at the same voltage as the inverting input. This causes a virtual ground at the inverting terminal of the op-amp.
The formula to calculate the output voltage (Vout) of a summing amplifier is:
Vout = - (Rf/R1 * V1 + Rf/R2 * V2 + ... + Rf/Rn * Vn)
Where:
Rf is the feedback resistor connected from the output to the inverting input of the op-amp.
R1, R2, ..., Rn are the input resistors connected to the inverting input.
V1, V2, ..., Vn are the input voltages.
As the name suggests, the summing amplifier adds all the input voltages together, with each input voltage multiplied by a scaling factor of (Rf/Ri) due to the configuration of the resistors. The negative sign in the formula indicates that the output signal is inverted relative to the input voltages.
It's worth noting that for precise summing operations, it is important to use precision resistors to ensure accurate scaling and minimize errors. Summing amplifiers are commonly used in various applications, such as audio mixers, analog signal processing, and analog computation tasks that require adding multiple signals together.