Patent ID: 7002398

Claim:
A circuit, comprising: a first transistor disposed in a first substrate having first, second and third terminals, the first terminal of the first transistor coupled to an external voltage, wherein a voltage provided at the third terminal of the first transistor is substantially proportional to a voltage between the first and second terminals of the first transistor when the voltage between the first and second terminals of the first transistor is less than a pinch-off voltage of the first transistor, wherein the voltage provided at the third terminal of the first transistor is substantially constant and less than the voltage between the first and second terminals of the first transistor when the voltage between the first and second terminals of the first transistor is greater than the pinch-off voltage of the first transistor; a control circuit disposed in the first substrate and coupled to the third terminal of the first transistor; and a second transistor disposed in a second substrate, a first terminal of the second transistor coupled to the external voltage.