Patent ID: 8004350

Claim:
An apparatus comprising: a first transistor circuit having a first overdrive voltage, wherein the first overdrive voltage is defined by a gate-source voltage of the first transistor circuit minus a threshold voltage of the first transistor circuit; and a second transistor circuit having a second overdrive voltage, wherein the second overdrive voltage is defined by a gate-source voltage of the second transistor circuit minus a threshold voltage of the second transistor circuit, and wherein the second transistor circuit is placed in a current mirror type arrangement with the first transistor circuit, wherein an impedance of the second transistor circuit increases as the second overdrive voltage decreases with respect to the first overdrive voltage and wherein the threshold voltage of the second transistor circuit is higher than the threshold voltage of the first transistor circuit and the gate-source voltage of the second transistor circuit is approximately equal to the qate-source voltage of the first transistor circuit.