DS100DF410 Datasheet, PDF (34/43 Pages) Texas Instruments – Low Power 10GbE Quad Channel Retimer

DS100DF410
SNLS399A – JANUARY 2012 – REVISED FEBRUARY 2013
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The DS100DF410 can invert the polarity of the data signals by means of a register write. Writing a 1 to bit 7 of
register 0x1f inverts the polarity of the output signal for the selected channel. This can provide additional flexibility
in system design and board layout.
Overriding the Figure of Merit for Adaptation
Register 0x2c, bits 5:4, Register 0x31, bits 6:5, Register 0x6b, Register 0x6c, Register 0x6d, and Register 0x6e,
bits 7 and 6
The default figure of merit for both the CTLE and DFE adaptation is simple. The horizontal and vertical eye
openings are measured for each CTLE boost setting or set of DFE tap weights and polarities. The vertical eye
opening is scaled to a constant reference vertical eye opening and the smaller of the horizontal or vertical eye
opening is taken as the figure of merit for that set of equalizer settings. The objective is to adapt the equalizer to
a point where the horizontal and vertical eye openings are both as large as possible. This usually provides
optimum bit error rate performance for most transmission channels.
In some systems the adaptation can reach a better setting if only the horizontal or vertical eye opening is used to
compute the figure of merit rather than using both. This will be system-dependent and the user must determine
through experiment whether this provides better adaptation in the user's system. For the DS100DF410, the DFE
figure of merit type can be set using register 0x2c, bits 5:4. The value of this two-bit field versus the configured
figure of merit type is shown in Table 10.
Register 0x2c, bits 5:4
0x0
0x1
0x2
0x3
Table 10. Figure of Merit Type Setting
Figure of Merit Type
Both HEO and VEO are used
Only HEO is used
Only VEO is used
Both HEO and VEO are used (default)
The CTLE figure of merit type is selected using the two-bit field in register 0x31, bits 6:5, with the same effect as
in Table 10.
For some transmission media the adaptation can reach a better setting if a different figure of merit is used. The
DS100DF410 includes the capability of adapting based on a configurable figure of merit. The configurable figure
of merit is structured as shown in the equation below.
FOM = (HEO – b) X a + (VEO – c) x (1 – a)
In this equation, HEO is horizontal eye opening, VEO is vertical eye opening, FOM is the figure of merit, and the
factors a, b, and c are set using registers 0x6b, 0x6c, and 0x6d respectively.
In order to use the configurable figure of merit, the enable bits must be set. To use the configurable figure of
merit for the CTLE adaptation, set bit 7 of register 0x6e, the en_new_fom_ctle bit. To use the configurable figure
of merit for the DFE adaptation set bit 6 of register 0x6e, the en_new_fom_dfe bit. The same scaling factors are
used for both CTLE and DFE adaptation when the configurable figure of merit is enabled.
Setting the Rate and Subrate for Lock Acquisition
Register 0x2f, bits 7:6 and 5:4
The rate and subrate settings, which configure the set of VCO frequencies to which the VCO coarse tuning is to
be calibrated are set using channel register 0x2f. Bits 7:6 are RATE<1:0>, and bits 5:4 are SUBRATE<1:0>.
Setting the Adaptation/Lock Mode
Register 0x31, bits 6:5, and Register 0x33, bits 7:4 and 3:0, Register 0x34, bits 3:0, Register 0x35, bits 4:0,
Register 0x3e, bit 7, and Register 0x6a
There are four adaptation modes available in the DS100DF410.
• Mode 0: The user is responsible for setting the CTLE and DFE values. this mode is used if the transmission
channel response is fixed.
• Mode 1: Only the CTLE is adapted to equalize the transmission channel. The DFE is enabled but the tap
weights are all set to 0. This mode is primarily used for smoothly-varying high-loss transmission channels
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