Method and apparatus for feedback control of I/O characteristics of digital interface circuits

A driver interface circuit comprising:

• input logic gate means for receiving input signals, said input logic gate means including a first logic gate of a predefined type having a first current transfer characteristic governed by a gate control voltage wherein in accordance with said first current transfer characteristic said first logic gate includes a first logical inverter for providing output signals of a first level in response to a first range of said input signals less than a predefined threshold and includes a second logical inverter for providing output signals of a second level in response to a second range of said input signals greater than said predefined threshold, said input logic gate means further including switch means for connecting said feedback line to a first control terminal of said first logic gate when input signals within said first range are received by said input logic gate means, and for connecting said first control terminal to a predefined gate control voltage when input signals within said second range are received by said input logic gate means;
• and
• compensation means for adjusting said gate control voltage, including a compensation gate of said predefined type having a current transfer characteristic proportional to said first current transfer characteristic, and feedback loop means connected between said compensation gate and said input logic gate for varying said gate control voltage until current flowing through said compensation gate matches a supply current provided to said input logic gate, said compensation means including a differential amplifier for impressing said gate control voltage on a feedback line, said amplifier including a first input connected to an output of said compensation gate and a second input connected to a predefined reference voltage of said first level.

A transceiver network comprising:

• a receiver circuit, said receiver circuit including:
• a CMOS input inverter that provides output signals in response to input signals in accordance with a first transfer characteristic governed by a first reference voltage, and
• first compensation means for adjusting said first reference voltage, including a first CMOS compensation inverter having an output governed by said first reference voltage, and first feedback loop means connected between said first compensation gate's output and said CMOS input inverter for varying said first reference voltage until said first compensation gate generates a predefined output signal;
• and
• a driver circuit, said driver circuit including:
• an first MOS gate having a first current transfer characteristic governed by a gate control voltage, and
• second compensation means for adjusting said gate control voltage, including a second MOS gate having a current transfer characteristic proportional to said first current transfer characteristic, and second feedback loop means connected between said second MOS gate and said first MOS gate for varying said gate control voltage until current flowing through said second MOS gate matches a supply current provided to said first MOS gate.