Switchable, uninterruptible reference generator with low bias current

Abstract

A switchable, uninterruptible, low-current reference generator with zero off-state current includes a cross-coupled, cascodeal .increment.V.sub.be current reference (70,72,74,76,78) for providing an output current, a current mirror (66,68) coupled in a cascode configuration with the current reference, and a start-up circuit (12) responsive to the absence of the output current for generating a start-up current (I.sub.58) to the current mirror. Start-up current is disabled when output current is restored, and the current mirror bootstraps the output current into regulation. Standby logic (10), comprising FET's configured as CMOS inverters, provides a TTL-compatible, active-low input, and switching FET's (60,80,90,92,94) responsive to the standby logic ensure that the reference generator draws no current in its off state. When the reference generator is turned on, a hysteresis circuit (98,52) coupled to the standby logic (10) increases the input voltage required for turn-off. The disclosed reference generator provides a bias current with a very low temperature coefficient and very little supply dependence. It has an active-low logic implementation with switching near the TTL range. It uses very little overhead current, and it cannot be forced permanently out of regulation by system transients. Because the start-up scheme uses actual detection of the absence of a bias current as its trigger, the reference generator will restart without the need for power supply ramping in the event of loss of bias during operation.