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ADS6224 LVDS output voltage swing

Calum Mackinnon
Genius 4155 points
Other Parts Discussed in Thread: ADS6224

Hey,

I am currently using the ADS6224 in our new design and am starting to do verification testing and am seeing larger than specified voltage on the LVDS data lines from the ADC. I have attached one of the scope pictures of the clock line. The data lines are the same.

As you can see, I am getting 850mv(including under and overshoot) measured across a 100ohm termination resistor. I am using a high speed differential probe.The datasheet states I should have 3.5mA across a 100ohm resistor or 350mv. I can't figure out why this part is putting out so much voltage. All the register setting are the default settings - I am not in double current mode.

Would you expect  350mV swing or does 750mV make sense?


Cheers

Calum

  • 0
    TI__Mastermind 29220 points

    Hi,

    The 3.5mA into a 100 ohm load from the LVDS driver changes direction depending on whether the output value is to be a '1' or a '0' so the voltage across the 100 ohm termination ranges from +350mV to -350mV so the differential probe will show you a 700 mV peak to peak differential swing or a 350mV swing looking at one side of the signal at a time with a single ended probe.    If you move the cursors down to the 'flat' spots of the signal instead of catching the overshoot/undershoot I thinkyou will see a swing closer to 350mV.  There will be some tolerance about that 3.5mA so there will be some variation in what the swing really is, but from your scope shot it looks about right to me.  With the overshoot/undershoot the scope is reporting Vmax of about 450mV and Vmin of about -400mV.  I think it would be closer to +350 and -350 if you didn't look at the overshoot.

    Regards,

    Richard P.