One of the most important specifications of an op amp is its input-offset voltage. You can null out this voltage on many op amps, but the problem with determining the input-offset voltage is that the offset voltage varies with temperature, flicker noise, and long-term drift. Chopping and au-tozeroing techniques have been around for several years, reducing achievable input offset to microvolts or less. The accuracy is so good that other minuscule effects, such as copper-solder thermocouple junctions, dominate the errors, until, with some effort, you can overcome them, as well. This Design Idea introduces a new type of chopping. "Chopping the noise gain" is a simple way to measure the offset voltage in real time, so that you can subtract it and enhance dc precision.
展开▼
