Self-Correcting Op-Amp Input Offset Using Analog Floating Gates

Abstract

Low input offset is important in high precision Op-Amps. However, input offset errors caused by mismatch in differential signal paths as a result of random variations are unavoidable even with optimum layout techniques. A relatively new method, the use of Analog Floating Gate (AFG) devices, to enable correction is studied. AFG devices act as analog storage and allow precise trimming of input offset. The proposed methodology results in offset correction for continuous time operation, provides low power operation, does not limit bandwidth and avoids discrete errors seen with some correction methods. Unlike some other analog memories, AFG devices tend to lose charge over time, typically a few mV per year. As a result, we have developed circuitry that automatically recalibrates the AFG charge and retains the Op-amp offset target throughout the product lifetime.