Datasheet

TUSB7320, TUSB7340
SLLSE76E–MARCH 2011– REVISED JULY 2011 www.ti.com
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
% dB
0000 0 0
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.
100 PHY CONTROL Copyright © 2011, Texas Instruments Incorporated
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