Digital Signal Processing Reference
In-Depth Information
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Figure 12-17
Impact of 6-dB loss on the eye for a sinusoidal signal: (a) lossless; (b)
6-dB loss.
close the eye of a sinusoid. Note that we chose a 1-V swing, 1-GHz signal for
illustration, but that the 6-dB rule is independent of swing and frequency. What
does depend on frequency is where the 6-dB loss point actually occurs.
Figure 12-18 portrays the eye diagram for a 10-Gb/s signal traveling across
the 0.381-m-long differential PCB transmission-line pair from Example 12-1.
Given a 500-mV signal swing and a 300-bit random sequence at the transmitter
output, we find that the eye at the receiver in Figure 12-18a is completely closed.
Figure 12-18b shows that the equalizer improves the situation considerably, pro-
viding an eye opening of approximately 55 ps and 40 mV. Comparison of the
eyes shows that the equalizer reduces the maximum signal swing from 430 mV
at the receiver (Figure 12-18a) input to 250 mV at the output of the equalizer
(Figure 12-18b).
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