Patent ID: 6815980
Filing Date: 2004-11-09
Classification: H04L

Abstract:
A method for terminating a differential transmission line based on a type of load activated through said transmission line, said transmission line comprising first and second differential signal lines, said method comprising the steps of:providing as an integrated circuit a plurality of resistive sub circuits for terminating said transmission line, each of said resistive sub circuits comprising a PFET; an NFET in parallel with said PFET; a first resistor connected at one end to a drain of said NFET and a source of said PFET, and connected at an opposite end to said first differential signal line of said differential transmission line; and a second resistor connected at one end to a source of said NFET and a drain of said PFET, and connected at an opposite end to said second differential signal line of said differential transmission line; and wherein there is a substantially open circuit between said first and second differential signal lines at an end of said transmission line adjacent to said load, other than said plurality of resistive subcircuits when activated and an input resistance of said load; when said type of load requires termination of said transmission line with approximately a same impedance as an impedance of said transmission line, activating one or more or said plurality of resistive subcircuits to provide approximately said same impedance to terminate said transmission line; and when said type of load requires termination of said transmission line with substantially open circuit impedance, deactivating all of said plurality of resistive subcircuits to provide substantially open circuit termination impedance except for said input resistance of said load.