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LVDS buffers in high speed ADCs?

fernando henrique cardoso
Prodigy 80 points
Other Parts Discussed in Thread: ADC16DV160, ADS5483

Hello Guys

We are designing an ADC FMC card with 4 channels. We intend to prototype two boards, with two different converters, one running at maximum 130 MSPS and other with maximum 250 MSPS, both are16 bits ADC´s. These boards will be attached to an AMC standard processing board, with FPGA.

My questions is: I read some topics on the internet about the recomendation to use buffers in the ADC´s digital outputs to get best performance on ADCs. We know that CMOS output is not suitable for long path BUS and also we need to minmize the capacitance on the digital traces to reduce voltage peaks, and so on. It´s necessary to use buffers also for LVDS signaling?

Are there rules to routing the digital traces on high speed ADC´s like ADS5483 or ADC16DV160? 

thank you very much!

Regards

Fernando Henrique Cardoso

fcardoso@lnls.br

+55-19-82156023

  • 0
    TI__Expert 4340 points

    Fernando,

    I think there are 2 concerns would lead someone to put down LVDS buffers: 1) There is noise on the carrier board and the buffers help isolate the ADC from that noise, or 2) LVDS drive strength, propagation attenuation and other signal integrity issues.

    If you're LVDS routing is 8 inches or less, you shouldn't have a problem. Even then, if you're timing is really tight, the trace characteristic impedance is uniform and the trace losses low, you can go farther.

    I have not run into noise coupling back via the LVDS traces from the receiver.

    Ground isolation can be important because the carrier card will typically have a lot of processing power that may cause ground noise. Using LVDS buffers can assist the signals jump the ground plane split without causing noisy disturbances as the signal jumps across the planes and experiences the impedance hiccup. It may be prudent to split the ground planes at the LVDS buffers and have the carrier card power the buffers. Just be careful that the ground split doesn't interfere with the return paths of drawing power from the carrier board such as from VADJ.

    Regards, Josh