17.1. Single-Bit Response

To understand how signal integrity issues, such as attenuation, dispersion, and reflections, affect the received signal quality, the single-bit response (SBR) is often used. The SBR is the channel response observed at the receiver, when the transmitter sends an unequalized single-bit-wide pulse (Figure 2.11 provides an example). Each circle on the SBR represents the symbol sample time. Here, several phenomena can be observed simultaneously: The spreading of the narrow pulse (beyond a single bit time) shows the dispersion of the channel, whereas the ripples (later in the SBR) are the reflections due to the impedance discontinuities. Any non-zero energy at other bit times in the single-bit response is referred to as inter-symbol interference (ISI). ISI corrupts the signal received at other bit times, and may lead to bit failure (as illustrated in Figure 2.12). Finally, the reduction in the peak amplitude shows that the SBR was attenuated when it passed through the channel.