TMDS171 Datasheet, PDF (26/62 Pages) Texas Instruments – 3.4 Gbps TMDS RETIMER

TMDS171, TMDS171I
SLLSEN7A – OCTOBER 2015 – REVISED DECEMBER 2015
www.ti.com
As there are times that true pre-emphasis may be the best solution there are two methods to accomplish this. If
pin strapping is being used the best method is to reduce the VSADJ resistor value thus increasing the V_OD swing
and then pulling the PRE_SEL pin to ground using a 65 kΩ resistor, see Figure 28. If using I²C there are two
methods to accomplish this. The first is similar to pin strapping but reducing VSADJ resistor value and then
implementing - 2 db de-emphasis through I²C, reg0Ch[1:0] = 01. The second method is to increase the VOD
swing by setting reg0Ch[7:5] = 011 and reg0Ch[1:0] = 01 which will accomplish the same pre-emphasis value,
see Figure 29. Note: De-emphasis is only implement able during retimer mode. In redriver mode this function is
not available.
PRE_SEL = Z
Vsadj = 7.06<Q
PRE_SEL = L
Vsadj = 4.5<Q
1^st bit
VOD(PP) = 1400mVpp
2^nd to N bit
VOD(SS) = 1150mVpp
Figure 28. Pre-emphasis Using Pin Strapping
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