Ultra-low constant-current generation with MOS interface-trap charge pump

We explore the MOS interface-trap charge-pump (ITCP) as an ultra-low constant-current generator for analog CMOS applications. Switched-capacitor (SC) techniques are generally suitable for ultra-low current generation because the current can be linearly controlled by frequency regardless of the level of current. ITCP has the same property but the minimum charge it puts out per cycle is at least two orders of magnitude smaller than that of an SC core. This helps generate the same current more accurately at a much higher frequency with a much smaller filter capacitance. The paper presents an optimized current generator configuration of rail-to-rail output range, zero temperature coefficient and very high output resistance. Transconductor circuits built with the charge pump are presented and experimentally evaluated.