Reflection and crosstalk in logic circuit interconnections

Digital logic circuits are now available and are being used with delay times that are comparable to the delays of interconnections used in packaging these circuits. At high speeds, however, such interconnections no longer behave as simple short circuits, but take on the appearance of transmission lines. Unless transmission lines are terminated properly, ``reflections´´ can develop that might be of sufficient magnitude to produce false logic levels or exceed maximum circuit voltage specifications. One may choose to solve the problem by increasing the density of the system. This, however, introduces the problem of ``crosstalk.´´ The present article describes several analytical techniques for predicting the kinds of reflections and crosstalk that are typically seen in digital systems, thus enabling the engineer to determine in advance whether or not such ``interconnection noise´´ will result, how bad it will be, and what the typical interconnection limitations are for circuits of various speeds.