Floating gate current mirror for gain correction in CMOS translinear circuits

The exponential behavior of MOSFETs in subthreshold operation has recently been exploited to build CMOS translinear circuits such as multipliers and log-domain filters. A major obstacle in developing a practical CMOS implementation is the variation in threshold voltage between devices. In translinear circuits, these voltage offsets manifest themselves as gain errors in the current-mode outputs. We have designed a floating-gate CMOS current mirror that can adapt its gain to compensate for these errors. The adaptation process uses only hot-electron injection, so the high voltages typically associated with tunneling are not needed. A small array of these circuits were fabricated in a standard 1.2 pm double-poly CMOS process. We demonstrate gain adaptation and discuss the nonlinearity introduced by the adaptive mirror.