Patent ID: 8829983

Claim:
An apparatus, comprising: an output driver; and a bias voltage controller coupled to provide a first bias voltage and a second bias voltage to the output driver; wherein the bias voltage controller comprises: a bias generator coupled to a first voltage supply, a second voltage supply, and a ground node; wherein the bias generator has a first bias node for sourcing the first bias voltage; wherein the first voltage supply is configured to provide a higher voltage level than the second voltage supply; a resistor-divider network coupled to the first voltage supply and the ground node; a watch dog circuit coupled to the resistor-divider network, bias generator, and the ground node; and a comparison circuit coupled to the bias generator and the second voltage supply; wherein the comparison circuit has a second bias node for sourcing the second bias voltage; wherein the watch dog circuit is configured to detect when the second voltage supply is below a voltage level to electrically couple the first bias node to the ground node; and wherein the watch dog circuit is configured to detect when the second voltage supply is above the voltage level to electrically decouple the first bias node from the ground node.