A summing amplifier is a type of operational amplifier (op-amp) circuit that is designed to combine multiple input signals and produce a single output signal, which is the algebraic sum of the input signals multiplied by their corresponding gain factors. This circuit is commonly used in various applications such as audio mixers, signal processing, and instrumentation.
The basic configuration of a summing amplifier consists of an operational amplifier (op-amp) with multiple input resistors connected to its inverting (-) input terminal. Each input signal is connected through a separate input resistor, and the other end of each resistor is connected to a common node, often referred to as the "summing junction."
The output of the summing amplifier is taken from the op-amp's output terminal, and its value is determined by the weighted sum of the input signals. The gain of each input signal is determined by the ratio of the feedback resistor (connected between the output and inverting input of the op-amp) to the corresponding input resistor. Mathematically, the output voltage (Vout) of a summing amplifier can be calculated as:
Vout = - (Rf1/Rin1) * Vin1 - (Rf2/Rin2) * Vin2 - ... - (Rfn/Rinn) * Vinn
Where:
Rf1, Rf2, ..., Rfn are the feedback resistors for each input signal.
Rin1, Rin2, ..., Rinn are the input resistors for each input signal.
Vin1, Vin2, ..., Vinn are the respective input voltages.
By properly choosing the values of the feedback and input resistors, you can control the contribution of each input signal to the output. If the feedback resistor for an input is larger compared to the input resistor, the corresponding input signal will have a higher gain and therefore a stronger impact on the output. Conversely, if the feedback resistor is smaller, the input signal's contribution will be diminished.
In essence, a summing amplifier combines the input signals in a way that their amplitudes are scaled according to the ratios of the feedback and input resistors, and then these scaled signals are summed algebraically at the output. This allows you to create complex signal combinations and mix different inputs together in various applications.