Patent ID: 8274303

Claim:
In a Schmitt trigger circuit comprising an inverter coupled between first and second power supply voltage terminals, the inverter having an input terminal and an output terminal, and the Schmitt trigger circuit having a feedback transistor, a control electrode of the feedback transistor coupled to the output terminal of the inverter for receiving a feedback signal, a method for testing a high hysteresis threshold voltage and a low hysteresis threshold voltage of the Schmitt trigger circuit, the method comprising: providing a power supply voltage to the first and second power supply voltage terminals of the inverter; directly connecting the input terminal of the inverter to the output terminal of the inverter; decoupling the feedback signal from the control electrode of the feedback transistor; providing a first power supply voltage to the control electrode of the feedback transistor; measuring a first voltage at the input terminal of the inverter, wherein the first voltage corresponds to the high hysteresis threshold voltage; removing the first power supply voltage from the gate of the feedback transistor; providing a second power supply voltage to the control electrode of the feedback transistor, wherein the second power supply voltage is different than the first power supply voltage; and measuring a second voltage at the input terminal of the inverter, wherein the second voltage corresponds to the low hysteresis threshold voltage.