Simple Rules for Choosing Resistor Values in Adder-Subtractor Circuits

I want to take a linear combination of analog voltages with both positive and negative coefficients, using a single operational amplifier. In Figure 1, for example:

Z = 3 x 1 + 0.15 x 2 - 2.9 y 1               (1)

To minimize offset-current error, I want to keep the equivalent parallel resistance on both sides equal. Read full article


Dan Sheingold

Dan Sheingold

Dan Sheingold, editor of Analog Dialogue since 1969 (Vol. 3), received a BSEE “with distinction” from WPI in 1948 and an MSEE from Columbia University in 1949. After 19 years with George A. Philbrick Researches, Inc., working with and writing about applications of analog computers and operational amplifiers—including the editing of the widely distributed Applications Manual–Computing Amplifiers—he joined Analog Devices. At ADI, besides Analog Dialogue, he has edited books on data converters (several editions), nonlinear circuits, and transducer interfacing, as well as Richard Higgins’s Digital Signal Processing in VLSI. In 1990 he was elected a Fellow of the IEEE, “for contributions to the understanding and use of analog devices and data converters.”