by Tim Green, Linear Applications Engineering Manager, Burr-Brown Products from Texas Instruments
Part 10 of this series is the sixth and final verse of our familiar electrical engineering tune, “There must be six ways to leave your capacitive load stable.” The six ways are Riso, High Gain & CF, Noise Gain, Noise Gain & CF, Output Pin Compensation, and, what we cover here: Riso w/Dual Feedback.
This topology is very often used to buffer a precision reference integrated circuit. As a voltage buffer, the op amp circuit provides higher source and sink currents than can be originally driven from the precision reference. Although we will look specifically at the gain of one, voltage follower configuration, the Riso w/Dual Feedback can be used with gains greater than one with slight modifications to the formulae provided. We will look at the two dominant types of op amp topologies, bipolar emitter-follower and CMOS RRO. The analytical and synthesis steps and techniques will be similar, but there are subtle differences -- enough to warrant looking at each respective output topology. As an added bonus we will purposely violate our rule-of-thumb guide and create the BIG NOT to see the effects of improper stability compensation.