The summing amplifier adds the input voltages together after scaling them according to the input resistor values.
Summing Amplifier in the Lushprojects Simulator
Vout = - Rf ( V1/R1 + V2/R2 + V3/R3 )
The gain of each input depends on Rf and the input resistor.
Rf provides negative feedback.
The inverting input labelled "P" is a Virtual Earth.
The virtual earth comes about as follows ...
The op' amp' has a very high open loop gain.
If the op' amp' is not saturated and the output is a few volts, it follows that the potential at P is a few microvolts.
This is a very small voltage (close to zero) so it's called a virtual earth.
The Summing Circuit
Applications include ...
mixing audio signals
adding input voltages
digital to analogue conversion Summing DAC
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