Patent ID: 6486727
Filing Date: 2002-11-26
Classification: H02M

Abstract:
A low-power substrate bias generator comprising:an oscillator for generating pumping signals when activated, but being in a low-power state when disabled; a charge pump, receiving the pumping signals from the oscillator, for pumping charge from a substrate to reduce a substrate voltage to a target; a substrate comparator, sensing the substrate voltage and comparing the substrate voltage to a target, for disabling the oscillator when the substrate voltage has reached the target; wherein the substrate comparator further comprises: a reference-voltage generator for generating a current-reference voltage; a current switch, coupled to the reference-voltage generator, for switching a large current through the reference-voltage generator when the substrate comparator is in the higher-power state, but for switching a smaller current through the reference-voltage generator when the substrate comparator is in the lower-power state; wherein the reference-voltage generator switches the current-reference voltage between a first level for the higher-power state, and a second level for the lower-power state; a sensing transistor, receiving the substrate voltage, for modulating a larger current when the current-reference voltage is at the first level, but for modulating a smaller current when the current-reference voltage is at the second level, the sensing transistor modulating a current in response to changes in the substrate voltage; wherein the substrate comparator senses the substrate voltage more quickly when in the higher-power state than when in the lower-power state, and a supply comparator, sensing a supply voltage and comparing a supply-independent reference voltage, for disabling the oscillator when the supply voltage is above a limit determined by the supply-independent reference voltage, whereby the oscillator is disabled, entering the low-power state, when the substrate reaches the target or when the supply voltage is above the limit and whereby rapid substrate sensing is provided before the substrate voltage reaches the target, but the lower-power state is entered after the target is reached.