Practical design for controlled impedance

A novel method for designing controlled impedance transmission lines for high-speed digital systems is introduced. The method requires specification of the desired electrical performance, some device parameters, and the desired characteristic impedance (Z₀ ). By following this procedure, the minimum and maximum Z ₀ values that meet electrical performance and the useful tolerances on the nominal Z₀ are maximized. The value of the termination resistor that maximizes the tolerances on Z ₀ is also obtained. In the ideal case of transmission line termination, the termination resistor matches the line impedance. In the practical case, the optimum series termination resistor for high-speed digital systems is less than the nominal line impedance. The optimum parallel termination resistor will have a higher value than the nominal line impedance