Page 398 - Op Amps Design, Applications, and Troubleshooting

374 ARITHMETIC FUNCTION CIRCUITS

Ohm's Law can be used to substitute resistance and voltage values.

Since all resistor values are equal (R), we can further simplify this latter expression
as follows:

We will come back to this equation momentarily. For now, though, let us deter-
mine the output voltage in terms of V x. Amplifier A 2 is a basic noninverting
amplifier with respect to V Xf since the left end of R 2 connects to ground (virtual
ground provided by the inverting input of AI). Therefore, the output voltage can
be expressed using our basic gain equation for noninverting amplifiers.

Since the resistors are all equal, we will substitute R for each resistor and solve the
equation for V x.

If we now substitute this last expression for V x into our earlier expression, we can
determine the output voltage in terms of input voltage. That is,