Common mode early voltage compensation subcircuit for current driver

A high speed current driver circuit comprising:

• (a) a biased driver circuit driving differential and common mode current signals containing information over a twisted pair cable, said driver circuit driving high, low and null signals representative of digital information, said driver circuit comprising:
• a first pair of transistors coupled to said twisted pair cable for driving differential signals;
• a second pair of transistors coupled to said twisted pair cable for driving common mode signals;
• and
• a third pair of transistors coupled to said twisted pair cable, said third pair of transistors for use in conjunction with said first pair and said second pair of transistors;
• and
• (b) a common mode early voltage compensation circuit coupled to said biased driver circuit, said common mode early voltage compensation circuit monitoring a bias voltage level and minimizing common mode current flow over said twisted pair cable in response to variations of said bias voltage level from a reference bias voltage.

A driver circuit for communicating information over a twisted pair cable, said driver circuit comprising:

• first circuitry for generating differential voltage signals over said twisted pair cable, said differential signals representative of binary data, said first circuitry having a bias voltage;
• second circuitry for generating a common mode voltage signal over said twisted pair cable, said second circuitry responsive to a speed signal input, and said common mode voltage signal for indicating a high speed transmission rate;
• and
• a common mode early voltage compensation circuit coupled to said first and second circuitry for monitoring said bias voltage and for minimizing common mode current flow over said twisted pair cable in response to variations of said bias voltage from a reference bias voltage level.

A communication network comprising:

• a plurality of communicating devices comprising a general purpose computer system, a digital graphic display device, a digital graphic input device, and a digital information storage device;
• and
• associated with individual devices of said network, a driver circuit for communicating information over a twisted pair cable, said driver circuit comprising:
• driving circuitry driving differential signals over said twisted pair cable and driving common mode current signals containing information over said twisted pair cable, said driving circuitry comprising driving transistors and having a bias voltage, said driving transistors coupled to said twisted pair cable;
• and
• a subcircuit coupled to said driving circuitry and modifying an effective common mode early voltage characteristic of said driving transistors responsive to variations in said bias voltage from a reference voltage level, said subcircuit effectively reducing common mode current flow over said twisted pair cable in response to variations of when said bias voltage from said reference voltage level.

In a communication device, a method of communicating information over a twisted pair cable, said method comprising the steps of:

• generating differential voltage signals over said twisted pair cable, said differential voltage signals representative of digital information for transmission, said step of generating differential voltage signals performed by a single driver circuit;
• generating common mode voltage signal over said twisted pair cable, said common mode voltage signal for signaling communication speed information, said step of generating common mode voltage signal also performed by said single driver circuit;
• monitoring a bias voltage of said single driver circuit;
• and
• minimizing common mode current flow over said twisted pair cable in response to variations of said bias voltage from a reference bias voltage level.