Low-power substrate bias generator disabled by comparators for supply over-voltage protection and bias target voltage

Abstract

A substrate bias generator has a ring oscillator disabled when a supply over-voltage condition is detected by a supply comparator, or when a target substrate voltage is reached. A substrate comparator compares the substrate voltage to a reference generated by a p-channel sense transistor that is independent of the substrate voltage. The substrate is sensed by an n-channel sense transistor with only its bulk connected to the substrate voltage. Current sources for the sense transistors and comparator are controlled by bias voltages generated by a voltage divider that switches from a high-power state to a low-power state once the substrate target is reached. Feedback turns off a high-current resistor, limiting current to that passing through a low-current resistor. The bias voltages are adjusted to reduce current to the sense transistors and comparator, reducing power. High current and power are used for fast sensing before the substrate target is reached.