Lattice Semiconductor ispXPGA Family Data Sheet
51
sysHSI Block Timing
Figure 24 provides a graphical representation of the SERDES receiver input requirements. It provides guidance on
a number of input parameters, including signal amplitude and rise time limits, noise and jitter limits, and P and N
input skew tolerance.
Figure 24. Receive Data Eye Diagram Template (Differential)
The data pattern eye opening at the receive end of a link is considered the ultimate measure of received signal
quality. Almost all detrimental characteristics of a transmit signal and the interconnection link design result in eye
closure. This combined with the eye-opening limitations of the line receiver can provide a good indication of a link’s
ability to transfer error-free data.
Signal jitter is of special interest to system designers. It is often the primary limiting characteristic of long digital
links and of systems with high noise level environments. An interesting characteristic of the clock and data recovery
(CDR) portion of the ispXPGA SERDES receiver is its ability to filter incoming signal jitter that is below the clock
recovery PLL bandwidth. For signals with high levels of low frequency jitter, the receiver can detect incoming data
error free, with eye openings significantly less than that shown in Figure 24.
eo
SIN
V
THD
200 mV Differential
+/- 100 mV Single Ended
jt
TH
Bit Time
jt
TH
: Optimum Threshold Crossing Jitter
jt
TH
