Analogue adder

An adder circuit is an electronic circuit that performs the algebraic addition of signals, either of voltage or of current. Circuits involving op amps are used to fulfil this purpose, with multiple independent voltage sources.

The circuit below is an inverting adder: By KCL, $v_o$ is given by:

$$v_o=-(\frac{R_F}{R_1}{v}_1+\frac{R_F}{R_2}{v}_2)$$

We can also take a special case where the $R_1=R_2=R$ when the weights are equal:

$$v_o=-\frac{R_F}{R}(v_1+v_2)$$

which can be generalised to the sum of all inputs connected to the op amp.

We can also build a non-inverting adder: If the input resistors are equal, where $R_1=R_2=\cdots =R_N$, then the output voltage is:

$$v_o=\frac{K}{N}\sum _{k=1}^N{v}_k$$

See also

• Digital adder