Supply voltage independent Schmitt trigger inverter

摘要

A Schmitt trigger inverter circuit can include a first inverter. The first inverter can include a first pull-up device, a first pull-down device and a second pull-down device. The first inverter can receive an input signal. The Schmitt trigger inverter circuit can include a second inverter coupled in series with the first inverter and including an output that generates an output signal. The Schmitt trigger inverter circuit further can include a switch coupled to the output of the second inverter circuit and that is selectively enabled by the output signal. The switch can couple a predetermined reference voltage to a source terminal of the first pull-down device when in an enabled state. Coupling the predetermined reference voltage to the source terminal of the first pull-down device can alter a threshold voltage of the Schmitt trigger inverter circuit.

主权项

1. A Schmitt trigger inverter circuit for use within an integrated circuit (IC), the circuit comprising:
a first inverter comprising a first pull-up device, a first pull-down device, and a second pull-down device, wherein the first inverter is configured to receive an input signal; a second inverter coupled in series with the first inverter and comprising an output configured to generate an output signal; a switch coupled to the output of the second inverter that is selectively enabled responsive to the output signal; wherein a source terminal of the second pull-down device is connected to a ground potential, and the switch is configured to couple a predetermined reference voltage to a source terminal of the first pull-down device when in an enabled state, the reference voltage being greater than the ground potential and less than a supply voltage powering the Schmitt trigger inverter circuit; wherein in response to the coupling of the predetermined reference voltage, a threshold voltage of the Schmitt trigger inverter circuit is altered such that the output signal of the second inverter is limited to a voltage range between the ground potential and the reference voltage, and the output signal is approximately equal to the reference voltage in response to the input signal being equal to the supply voltage.