Schmitt trigger circuit having mismatched input and supply

A system comprising:

• a logic circuit adapted to be coupled to a first voltage supply;
• a load circuit;
• and
• a buffer circuit coupled between the logic circuit and the load circuit, the buffer circuit including:
• an inverter including:
• a first pull-down transistor having a control terminal and first and second terminals, the first terminal adapted to be coupled to a second voltage supply;
• a second pull-down transistor having a control terminal and first and second terminals, the first terminal of the second pull-down transistor coupled to the second terminal of the first pull-down transistor;
• a pull-up resistor having first and second terminals, the first terminal of the pull-up resistor adapted to be coupled to a third voltage supply that provides a voltage higher than a voltage of the first voltage supply;
• and
• a pull-up transistor having a control terminal and first and second terminals, the first terminal of the pull-up transistor coupled to the second terminal of the pull-up resistor, the second terminal of the pull-up transistor coupled to the second terminal of the second pull-down transistor, the control terminals of the first and second pull-down transistors and the pull-up transistor coupled together, wherein a threshold voltage of the first pull-down transistor is less than a threshold voltage of the pull-up transistor, and a threshold voltage of the second pull-down transistor is less than the threshold voltage of the first pull-down transistor;
• a hysteresis transistor having a control terminal and first and second terminals, the control terminal of the hysteresis transistor coupled to the second terminals of the pull-up transistor and the second pull-down transistor, the first terminal of the hysteresis transistor coupled to the second terminal of the pull-up resistor and to the first terminal of the pull-up transistor, the second terminal of the hysteresis transistor coupled to the first terminal of the first pull-down transistor;
• and
• a clamp circuit having a first terminal coupled to the first terminal of the first pull-down transistor and having a second terminal coupled to the second terminal of the first pull-down transistor.

A circuit comprising:

• a first transistor having a control terminal and first and second terminals, the first terminal adapted to be coupled to a first voltage supply terminal;
• a second transistor having a control terminal and first and second terminals, the first terminal of the second transistor coupled to the second terminal of the first transistor;
• a resistor having first and second terminals, the first terminal of the resistor adapted to be coupled to a second voltage supply terminal;
• a third transistor having a control terminal and first and second terminals, the first terminal of the third transistor coupled to the second terminal of the resistor, the second terminal of the third transistor coupled to the second terminal of the second transistor, the control terminals of the first, second, and third transistors coupled together;
• a fourth transistor having a control terminal and first and second terminals, the control terminal of the fourth transistor coupled to the second terminals of the second and third transistors, the first terminal of the fourth transistor coupled to the second terminal of the resistor and to the first terminal of the third transistor, the second terminal of the fourth transistor coupled to the first terminal of the first transistor;
• and
• a clamp circuit having a first terminal coupled to the first terminal of the first transistor and having a second terminal coupled to the second terminal of the first transistor.