The effect of rise time upon pulse shape and cross talk in high-speed digital interconnects

Abstract

A lossy model for microstrip lines has been implemented in the SPICE simulator to inestigate the effect of rise time of an input signal upon the output waeforms. The leel of ringing and pulse deformation are found to be related to the fast rise time gien the circuit layout and parameters. The limits to the speed and pulse width of an input signal hae been predicted for appropriate logic functions. Q 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 328)331, 1997. Recent advances made in high-speed digital integrated cir- cuits technology has reduced the single device switching time to a few picoseconds. However, the interconnection delay time between the devices is often significantly longer than device switching time. Therefore, in such cases one can no longer ignore the transmission-line property of the intercon- nections. Accurate modeling and simulation of the effect of the rise time of a signal traveling along the transmission lines has become very important, because changes in the rise time wx may lead to distortion of the desired logic functions 1) 3. The faster the rise time, the more ringing and distortion to the output signal will occur. Excess ringing may cause a logic error in the received signal, as the voltage level may pass through the critical logic voltage levels more than once in a single pulse. Distortion to the signal shape may also be detrimental, as the length of the pulse may either become shorter or longer than the critical length. If a series of pulses are sent and their width increases, errors in timing are likely to occur and to propagate further on through the system until the signal no longer resembles the original. It is therefore important that the fastest possible rise time is calculated, so that the interconnect can be evaluated for its suitability in a particular application, such as a high-speed digital circuit, where excess ringing may introduce severe signal distortion wx and induce an error in logic on a neighboring line 3 . The purpose of this article is to present the results of modeling work on the effect of signal rise time upon pulse shape and cross talk between neighboring lines on a high-speed inter- connection bus. All simulations in this article are carried out with the use of the example of an eight-line bus in a high-