Method and apparatus for driving a signal using switchable on-die termination

A circuit, comprising:

• first means for electrically connecting to a first power line and a bus line of an assisted Gunning transceiver logic (AGTL) bus when enabled, the first means having an impedance that substantially matches the bus line's characteristic impedance, wherein the first means is a P-channel transistor and the second means is an N-channel transistor;
• second means for electrically connecting a second power line and the bus line when enabled, the second means having an impedance different from that of the first means, wherein the second means is disabled when the first means is enabled and is enabled when the first means is disabled;
• and
• a trim circuit coupled to the P-channel transistor, wherein the trim circuit is to compare the impedance of the first means to a reference impedance and to adjust the impedance of the first means to substantially match the reference impedance.

A system, comprising:

• an assisted Gunning transceiver logic (AGTL) bus;
• a first driver/receiver circuit coupled to one end of a bus line of the AGTL-type bus, the first driver/receiver circuit including:
• a first pull-up switch unit to couple a first power line to the bus line, wherein the first pull-up switch unit has an impedance substantially matching the bus line's characteristic impedance, wherein the first pull-up switch unit is a P-channel transistor having one terminal coupled to the first power line;
• a first pull-down switch unit coupled to a first ground line and to the bus line, wherein the first pull-down switch unit has an impedance different from that of the first pull-up switch unit;
• and
• a second driver/receiver circuit coupled to another end of the bus line, the second driver/receiver circuit including:
• a second pull-up switch unit to electrically connect a second power line to the bus line, the first and second power lines having substantially identical voltage levels, wherein the second pull-up switch unit has an impedance substantially matching that of the first pull-up switch unit,
• a second pull-down switch unit coupled to a second ground line and to the bus line, the first and second ground lines having substantially identical voltage levels, wherein the second pull-down switch unit has an impedance substantially matching that of the first pull-down switch unit;
• and
• a trim circuit coupled to the P-channel transistor, wherein the trim circuit is to compare the impedance of the first pull-up switch unit to a reference impedance and to adjust the impedance of the first pull-up switch unit to substantially match that of the reference impedance.