DS110RT410 Datasheet, PDF (33/40 Pages) Texas Instruments – DS110RT410 Low Power Multi-Rate Quad Channel Retimer

DS110RT410
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SNLS460 – MAY 2013
For some transmission media the adaptation can reach a better setting if a different figure of merit is used. The
DS110RT410 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. The value of a is the 8-bit value in
register 0x6b divided by 255. It therefore ranges from 0 to 1.
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.
Setting the Adaptation/Lock Mode
Register 0x31, bits 6:5, Register 0x3e, bit 7, and Register 0x6a
There are four adaptation modes available in the DS110RT410.
• Mode 0: The user is responsible for setting the CTLE values. this mode is used if the transmission channel
response is fixed.
• Mode 1: Only the CTLE is adapted to equalize the transmission channel. This mode is primarily used for
smoothly-varying high-loss transmission channels such as cables and simple PCB traces.
Bits 6:5 of register 0x31 determine the adaptation mode to be used. The mapping of these register bits to the
adaptation algorithm is shown in Table 13.
Register 0x31, Bit 6
adapt_mode[1]
0
0
Table 13. DS110RT410 Adaptation Algorithm Settings
Register 0x31, Bit 5
adapt_mode[0]
0
1
Adapt Mode Setting <1:0>
00
01
Adaptation Algorithm
No Adaptation
Adapt CTLE Until Optimum
(Default)
By default the DS110RT410 requires that the equalized internal eye exhibit horizontal and vertical eye openings
greater than a pre-set minimum in order to declare a successful lock. The minimum values are set in register
0x6a.
The DS110RT410 continuously monitors the horizontal and vertical eye openings while it is in lock. If the eye
opening falls below the threshold set in register 0x6a, the DS110RT410 will declare a loss of lock.
The continuous monitoring of the horizontal and vertical eye openings may be disabled by clearing bit 7 of
register 0x3e.
Initiating Adaptation
Register 0x24, bit 2, and Register 0x2f, bit 0
When the DS110RT410 becomes unlocked, it will automatically try to acquire lock. If an adaptation mode is
selected using bits 6:5 in register 0x31, the DS125RT410 will also try to adapt its CTLE.
Adaptation can also be initiated by the user. CTLE adaptation can be initiated by setting and then clearing
register 0x2f, bit 0.
Overriding the CTLE Settings Used for CTLE Adaptation
Register 0x2c, bits 3:0, Register 0x2f, bit 3, Register 0x39, bits 4:0, and Registers 0x50-0x5f
The CTLE adaptation algorithm operates by setting the CTLE boost stage controls to a set of pre-determined
boost settings, each of which provides progressively more high-frequency boost. At each stage in the adaptation
process, the DS110RT410 attempts to phase lock to the equalized signal. If the phase lock succeeds, the
DS110RT410 measures the horizontal and vertical eye openings using the internal eye monitor circuit. The
DS110RT410 computes a figure of merit for the eye opening and compares it to the previous best value of the
figure of merit. While the figure of merit continues to improve, the DS110RT410 continues to try additional values
of the CTLE boost setting until the figure of merit ceases to improve and begins to degrade. When the figure of
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