TUSB7320 datasheet(99/115 Pages) TI1

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TUSB7320, TUSB7340

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SLLSE76J – MARCH 2011 – REVISED MAY 2012

8.2

De-Emphasis Control

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

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 via the PORTx_DE bits in the De-Emphasis

and Swing Control Register, see Section 4.65.

Table 8-2. Differential Output De-Emphasis

Amplitude Reduction

Value

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

8.3

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 via the Portx_EQ bits of the Equalizer Control Register, Section 4.66.

Table 8-3 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.

PHY CONTROL

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