Level shifter with low voltage loss

摘要

A system and method are disclosed for level shifting a DDC bus with a low voltage loss. A pull up circuit includes an NMOS transistor, a PMOS transistor and resistor. An NMOS pull up gate is also included in line with the DDC bus. When powered, the level shifter adjusts the voltage of transmitted signals to match the voltage of a receiving device. The resulting adjusted is slightly lower due to a threshold voltage lost across one or more transistors. Additionally, when unpowered, the level shifter releases the signal transmission line. Unadjusted signals can then be transmitted without consumption of power by the level shifter.

主权项

1. A method for voltage level shifting display data transmitted along a display data channel between a first video interface and a second video interface, the method comprising:
receiving at a voltage level shifter circuit a first signal from a first video interface operating at a first voltage level, the first signal having a voltage corresponding to the first voltage level; enabling a pull-up circuit to cause current to flow from a level shifter reference voltage source included in the level shifter circuit to the display data channel, responsive to receiving at least one pull-up circuit control signal having a first state; adjusting, using the voltage level shifter circuit, a voltage of the first signal to match a voltage of a second video interface, coupled to receive the first signal from the level shifter circuit using the display data channel, the second video interface operating at a second voltage level, the second voltage level having a value between zero and a value of the first voltage level; transmitting, the first signal with an adjusted voltage level to the second video interface using the display data channel; and disabling the pull-up circuit to block current from flowing from the display data channel to the level shifter reference voltage source when the level shifter circuit is powered off, responsive to receiving the at least one pull-up circuit control signal having a second state.