Output buffer with time varying source impedance for driving capacitively-terminated transmission lines

An output buffer waveform for driving a capacitively-terminated transmission line having a characteristic impedance Z0 and which conveys data bits during respective unit intervals, said waveform comprising:

• a first portion during which said waveform transitions between a first voltage V1 and a second voltage V2 between a time t1 and a time t2;
• a second portion during which said waveform remains fixed at said second voltage V2 until a time t3;
• a third portion during which said waveform transitions to a voltage V3 between V1 and V2 between time t3 and a time t4;
• and
• a fourth portion during which said waveform remains fixed at said third voltage V3 until a time t5;
• said output buffer waveform created within a unit interval whenever successive data bits transition between logic states;
• said first and second output buffer waveform portions generated with circuitry arranged such that voltage V2 is maximized, and said fourth output buffer waveform portion generated with circuitry which has a non-zero output impedance to absorb transitions reflected back to said circuitry by said capacitive termination.

A method of driving a capacitively-terminated transmission line having a characteristic impedance Z0 which conveys data bits during respective unit intervals, comprising:

• generating a waveform which varies with said data bits within a unit interval whenever successive data bits transition between logic states, said waveform generation comprising:
• generating, using a source having an output impedance Z1 which is much less than Z0, a first portion of said waveform during which said waveform transitions from a first voltage V1 to a second voltage V2 between a time t1 and a time t2;
• generating, using a source having an output impedance Z1 which is much less than Z0, a second portion of said waveform during which said waveform remains fixed at said second voltage V2 until a time t3;
• generating a third portion of said waveform during which said waveform transitions to a voltage V3 between V1 and V2 between time t3 and a time t4;
• and
• generating, using a source having a non-zero output impedance Z2 greater than Z1, a fourth portion of said waveform during which said waveform remains fixed at said third voltage V3 until a time t5.