Connectors in Very-High-Speed Digital Circuits

The properties of standard card edge, printed circuit, and flat cable connectors have been investigated from the point of view of transmitting pulses with very short rise times. A simple theory based on linear approximation of the leading and trailing edges of the actual pulse waveform is derived to predict the effect of impedance mismatch caused by the connector. Experimental confirmation of the theory, measurements of popular types of connectors, and extrapolation of experience with a 350-Mb/s logic network confirm that, under certain conditions, the currently available connectors can be used with pulse rise times longer than 250 ps and with interconnection impedances from 50 to 100 ohms. Transmission lines matched at both ends and/or balanced pairs are preferred for interconnections between different parts of a very fast (greater than 250-Mb/s) pulse system.