Feedback controlled substrate bias generator

Abstract

A feedback controlled substrate bias generator having a substrate bias level sensing circuit, a charge pump circuit and an improved oscillator is disclosed. The substrate bias level sensing circuit is coupled to a semiconductor substrate for sensing a bias voltage of the semiconductor substrate and outputting a control signal in response to the sensed bias voltage. The charge pump circuit is coupled to the semiconductor substrate and the substrate bias level sensing circuit for receiving a clock pulse and the control signal and supplying the bias voltage to the semiconductor substrate in response to the received signals. The improved oscillator is coupled to the charge pump circuit for generating the clock pulse. The improved oscillator has a loop circuit having a plurality of serially and circularly coupled inverters each of which has a source terminal applied to voltage from a voltage source, an input terminal for receiving an input signal and an output terminal for outputting an output signal. The improved oscillator further has a plurality of switches each of which has a control terminal, a first terminal coupled to the source terminal of a corresponding inverter of the loop circuit and a second terminal coupled to the voltage source. Each of the switches electrically cuts the first and second terminals when the input signal of the one of the inverters except for the corresponding inverter changes from one level to another.