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Signal Integrity: From High Speed to Radiofrequency Applications by Fabien Ndagijimana

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1

Degradation of Rise Time in Interconnects

Rise time is one of the main parameters of a digital signal: the higher the speed, the more rise time must be controlled. Interconnects generally behave like low-pass circuits, and propagation in limited bandwidth circuits leads to an increasing rise time, thus limiting the performance of transmission systems. This chapter discusses the degradation of rise time resulting from propagation in interconnects. We will focus on the relationship between the bandwidth of signals in the base band and the modifications in parameters of these signals, in particular rise time, when they propagate in a limited bandwidth channel.

1.1. Propagation issues in interconnects

Nowadays, circuit performances double practically every 18 months, with the consequent amplification of parasite effects in interconnects going from the chip to the printed circuit.

1.1.1. Evolution of digital circuits

Digital circuit speed has increased considerably since the 1990s, from a few megabits per second to several gigabits per second today. This is related to the progress of microelectronics, which follows Moore’s law: “a doubling of the number of transistors on the same size chip every 18 months”. In integrated circuits, the overall delay of a circuit is currently controlled largely by parasite delay in interconnects. These become an obstacle to improved performance in terms of speed, which is crucial given the growing demand for high-speed applications.

Figure 1.1. Interconnects ...

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