Integrated circuit buffer with controlled rise/fall time

An integrated circuit having a buffer comprising a pull-up transistor for raising the voltage on an output load during a rise time, and an n-channel pull-down transistor for reducing said voltage during a fall time;

• and means for generating a control voltage that maintains the fall time of said pull-down transistor relatively more constant with respect to at least one of the factors selected from the group consisting of:
• temperature, power supply voltage, and fabrication process speed,
• characterized in that said means for generating a control voltage comprises:
• a reference buffer comprising an n-channel pull-down transistor that discharges a reference capacitor by allowing current to flow from said capacitor through an impedance, thereby producing a voltage across said impedance;
• a sample-and-hold circuit for sampling the magnitude of said voltage in order to produce a sampled voltage;
• a band-gap reference for generating a constant-magnitude reference voltage;
• a band-gap reference for generating a constant-magnitude voltage;
• an operational amplifier for comparing the magnitude of said sampled voltage to said constant-magnitude reference voltage in order to generate said control voltage;
• and means for feeding the control voltage back to said reference buffer so as to cause said sampled magnitude to reach a steady-state value.

A method of operating an integrated circuit buffer that drives an output load at a switching speed, including the step of generating a control signal that maintains said speed relatively more constant with respect to at least one of the factors selected from the group consisting of:

• temperature, power supply voltage, and fabrication process speed,
• characterized in that said generating a control signal comprises:
• driving a refenence load with a drive current generated by a reference buffer;
• sampling the magnitude of the drive current to said reference load to obtain a sampled drive signal;
• and
• deriving said control signal from said sampled drive signal.