A summing amplifier, also known as an inverting summing amplifier, is a type of operational amplifier (op-amp) circuit that is designed to combine multiple input voltages and produce an output voltage that is the sum of the weighted input voltages. This circuit is commonly used in analog electronics and signal processing applications.
The basic configuration of a summing amplifier involves an operational amplifier (op-amp) with multiple input resistors connected to its inverting (-) input terminal. Each input voltage is fed through a separate resistor to the inverting input of the op-amp. The output of the op-amp is taken from its output terminal.
The ability of a summing amplifier to combine inputs lies in its operation principle. The op-amp strives to maintain its inverting and non-inverting inputs at the same voltage level (virtual short-circuit). In a summing amplifier, the inverting input is used, and the op-amp's high input impedance prevents significant current from flowing into the inverting input terminal. Therefore, the current flowing through each input resistor is proportional to the input voltage applied to it.
The output voltage of the summing amplifier is determined by the sum of the weighted voltages at its inputs. The weight of each input voltage is determined by the ratio of the input resistor to the feedback resistor connected between the op-amp's output and inverting input. Mathematically, the output voltage (
out
V
out
) of the summing amplifier can be expressed as:
out
=
−
(
/
1
)
⋅
1
−
(
/
2
)
⋅
2
−
…
−
(
/
)
⋅
V
out
=−(R
f
/R
1
)⋅V
1
−(R
f
/R
2
)⋅V
2
−…−(R
f
/R
n
)⋅V
n
Where:
R
f
is the feedback resistor's resistance.
1
,
2
,
…
,
R
1
,R
2
,…,R
n
are the resistances of the input resistors.
1
,
2
,
…
,
V
1
,V
2
,…,V
n
are the input voltages.
By adjusting the values of the feedback resistor and the input resistors, you can control the scaling and polarity of each input voltage in the summing amplifier's output.
Summing amplifiers are widely used in applications like audio mixers, signal processing, and control systems where the combination of multiple input signals is required to create a desired output response.