Analysis of the effect of nonlinear input/output characteristics of digital integrated circuits on signal integrity

The paper studies the reflections of the signals transmitted over PCB traces in the case of nonlinear transmission line terminators. First, the features of the approach presented in (the case of constant terminators) are briefly recapitulated. Next, the improved simulator is presented. This last approach takes into consideration the input/output voltage-current characteristics of the digital circuits. This is necessary because in most of the cases, a nonlinear terminator terminates a transmission line having an input from any one of a plurality of logic types: emitter coupled logic (ECL), transistor logic (TTL), Schottky transistor logic (STTL), low power Schottky transistor transistor logic (LSTTL), complementary MOS (CMOS). Finally, we investigate the signals that appear on the track. Nonlinear elements-in particular, digital integrated circuits having a continuous piecewise-linear voltage-current characteristic-are considered to be the terminations of the line.