Schmitt trigger with test circuit and method for testing

In a Schmitt trigger circuit comprising a first transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode coupled to an input terminal to receive an input voltage;

• a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to an output terminal, and a control electrode coupled to the input terminal to receive the input voltage;
• a third transistor having a first current electrode coupled to the second current electrode of the second transistor at the output terminal, a second current electrode, and a control electrode coupled to the input terminal to receive the input voltage;
• a fourth transistor having a first current electrode coupled to the second current electrode of the third transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode coupled to the input terminal to receive the input voltage;
• a fifth transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to the second power supply voltage terminal, and a control electrode;
• a sixth transistor having a first current electrode coupled to the first power supply voltage terminal, a second current electrode coupled to the second current electrode of the third transistor, and a control electrode, a method for testing a high hysteresis threshold voltage and a low hysteresis threshold voltage of the Schmitt trigger, the method comprising:
• directly connecting the input terminal to the output terminal;
• providing a first power supply voltage to the control electrodes of the fifth and sixth transistors;
• measuring a first voltage at the input terminal, wherein the first voltage corresponds to the high hysteresis threshold voltage;
• removing the first power supply voltage from the control electrodes of the fifth and sixth transistors;
• providing a second power supply voltage to the control electrodes of the fifth and sixth transistors, the second power supply voltage being different than the first power supply voltage;
• and
• measuring a second voltage at the input terminal, wherein the second voltage corresponds to the low hysteresis threshold voltage.

A Schmitt trigger circuit comprising:

• a first transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode coupled to an input terminal for receiving an input voltage;
• a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to a circuit node, and a control electrode coupled to the input terminal to receive the input voltage;
• a third transistor having a first current electrode coupled to the second current electrode of the second transistor at the circuit node, a second current electrode, and a control electrode coupled to the input terminal to receive the input voltage;
• a fourth transistor having a first current electrode coupled to the second current electrode of the third transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode coupled to the input terminal to receive the input voltage;
• a fifth transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to the second power supply voltage terminal, and a control electrode coupled to the circuit node;
• and
• a test circuit for selectively directly connecting the input terminal to the circuit node, the test circuit for selectively decoupling the control electrode of the fifth transistor from the circuit node, and the test circuit for selectively applying the first and second power supply voltages to the control electrode of the fifth transistor.