TUSB7320 datasheet(13/117 Pages) TI1

13 / 117 page

TUSB7320, TUSB7340

www.ti.com

SLLSE76M – MARCH 2011 – REVISED JULY 2015

7.3.1.1.1

De-Emphasis Control

De-emphasis provides a means to compensate for high-frequency attenuation in the attached media. De-

emphasis causes the output amplitude to be smaller for bits which are not preceded by a transition than for bits

which are. Fifteen different de-emphasis settings are provided through the PORTx_DE bits in the De-Emphasis

and Swing Control Register.

Table 2. Differential Output De-Emphasis

VALUE

AMPLITUDE REDUCTION

0000

0001

5.33

-0.48

0010

9.52

-0.87

0011

13.8

-1.29

0100

18.1

-1.73

0101

22.5

-2.21

0110

27.0

-2.73

0111

31.4

-3.28

1000

36.2

-3.9

1001

40.8

-4.55

1010

45.4

-5.26

1011

50.2

-6.05

1100

55.0

-6.93

1101

59.7

-7.90

1110

64.5

-8.99

1111

69.3

-10.27

7.3.1.2 Adaptive Equalizer

All receive channels in this macro family incorporate an adaptive equalizer, which can compensate for channel

insertion loss by attenuating the low frequency components with respect to the high frequency components of the

signal, thereby reducing inter-symbol interference.

The equalizer can be configured through the Portx_EQ bits of the Equalizer Control Register. Table 3

summarizes the options, which are:

•

No adaptive equalization. The equalizer provides a flat response at the maximum gain. This setting may be

appropriate if jitter at the receiver occurs predominantly as a result of crosstalk rather than frequency

dependent loss.

•

Fully adaptive equalization. Both the low frequency gain and zero position of the equalizer are determined

algorithmically by analyzing the data patterns and transition positions in the received data. FTC refers to the

algorithm that controls the zero position. In the FTC normal mode, the zero is decreased in frequency when

more equalization is needed; in the FTC reversed mode, the zero is increased in frequency when more

equalization is needed. The fully adaptive with FTC reversed setting should be used for most applications.

•

Hold. The equalizer state is held at its current gain level and zero point.

•

Initialize. The equalizer is initialized to a mid-point gain level, with the zero set to a frequency appropriate for

the receiver data rate.

•

Partially adaptive equalization.

The low frequency gain of the equalizer is determined algorithmically by

analyzing the data patterns and transition positions in the received data. The zero position is fixed in one of

eight zero positions. For any given application, the optimal setting is a function of the loss characteristics of

the channel and the spectral density of the signal as well as the data rate, which means it is not possible to

identify the best setting by data rate alone, although generally speaking, the lower the line rate, the lower the

zero frequency that will be required.

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