Adder

A circuit diagram of an opamp in a adder configuration is shown in Figure 16.

**Figure 16:** Adder or summing amplifier.
$\begin{figure} \begin{center} \epsfig{file=images/opampimg4.eps}\end{center}\end{figure}$

This circuit has two inputs, and the basic input-output relation is

$\begin{displaymath}v_{out} = -\frac{R_2}{R_{1a}} v_{ina} -\frac{R_2}{R_{1b}} v_{inb} . \end{displaymath}$

(15)

Exercise. Derive formula (15). Hint: It is similar to the inverting amplifier.

PSPICE file: suma1.sch.

ANU Engineering - ENGN2211