Patent ID: 6057716
Filing Date: 2000-05-02
Classification: G01R

Abstract:
A circuit responsive to input control data for alternately operating in one of a drive mode and a termination mode as selected by said input control data, wherein when operating in the drive mode the circuit produces a differential output signal on first and second transmission lines with a logic state of said differential output signal being determined by said input control data, wherein when operating in said termination mode said circuit provides a load for a differential input signal arriving at said circuit on said first and second transmission lines, wherein each of said first and second transmission lines has a similar characteristic impedance, the circuit comprising:a first circuit node (72);a first resistor (69) having an impedance matching said characteristic impedance and linking said first transmission line to said first circuit node;a second resistor (70) having an impedance matching said characteristic impedance and linking said second transmission line to said first circuit node;current source means (62) for conducting a current;a first transistor (64) linking said first transmission line and said first resistor to said current source means such that when said first transistor is turned on at least a portion of said current passes from said first circuit node through said first resistor and through said first transistor;a second transistor (66) linking said second transmission line and said second resistor to said current source means such that when said second transistor is turned on at least a portion of said current passes from said first circuit node through said second resistor and through said second transistor; andcontrol means (75) connected to said current source means for adjusting a magnitude of said current conducted by said current source means in response to said input control data,wherein said control data controls a relative proportion of said current passing through each of said first and second transistors,wherein said current source means conducts said current of magnitude controlled by a magnitude of a control signal, andwherein said control means comprises:means (80, 82) for generating and applying said control signal to said current source, wherein the magnitude of said control signal is determined by said input control data; andvoltage source means (74, 76, 78) for generating and applying a node voltage to said first circuit node, wherein a magnitude of said node voltage is determined by said input control data.