EQUALIZATION - Advanced Signal Integrity for High-Speed Digital Design - page 512

0

− 3

CTLE

100% eye closure

− 6

− 9

− 23.5 dB

− 12

PCB

− 15

− 18.3 dB

− 18

100% eye closure

− 21

PCB + CTLE

− 24

− 27

− 30

0 1 2 3 4 5 6 7 8 9 10

Frequency (GHz)

(a)

2

0

− 2

0 0.5 1 1.5 2

Frequency (GHz)

(b)

PCB
CTLE
PCB

+ CTLE

Figure 12-16 Passive CTLE transfer function: (a) magnitude; (b) phase.

The other impact of the equalizer is that the overall swing is reduced in order to
achieve the reduction in minimum-to-maximum loss for the system. This “flatten-
ing” of the magnitude of the frequency response is a good qualitative way to view
the benefit of equalization. Even though we reduce the maximum signal swing of
the system, we realize a net gain because we have reduced the variation between
the maximum signal swing (low frequency) and the minimum signal swing (high
frequency). Figures 12-17 through 12-19 each illustrate this concept in slightly
different ways. In Figure 12-17 we see that a 6-dB loss is sufficient to completely