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TMDS1204: VOD and liner/limited mode

Nikita Alisov
Prodigy 160 points
Part Number: TMDS1204


Hello,

The re-driver has two option to operate in liner and limitad mode. VOD is setting of re-driver's output.

So base on my anderstanding in the liner mode the output voltage swing is fixed (as it works for re-timers), but in liner mode VOD setting is kind of cutter of the amplifying signal

I mean for instans:
input voltage sving: 600 mV
EQ setting: +6db (which means in general output voltage swing should be 1200 mV)
VDO seting: 1000mV 
than output voltage swing will be 1000 mV because 1000 mV VOD

Is my understanding correct?


Thank you

BR
Nikita

  • +1
    TI__Guru**** 181421 points

    Nikita

    For the linear mode, it sets the linearity range of the input, not the actual output amplitude. 

    The linearity range of the input is also a function of the TMDS1204 EQ Gain, 

    Max VID = VOD * (10^-(Gain/20))

    Assume we have an EQ gain of 5.5dB, then max VID = 1000 * (10^-(5.5/20)) = 530mV

    So if the input voltage swing is 600mV, we are already outside the max VID and output amplitude will be clamped. The TMDS1204 can operate outside the VOD linear range, but the jitter will be higher. We should reduce the input voltage swing to be < 530mV to stay within TMDS1204 linearity range. 

    If we reduce the input voltage swing to 500mV, then the output swing will be a function of the input DC gain and amplitude. DC Gain = 10 * Log (Vout/Vin).

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 160 points

    I see, thank you very much!