DAC38J84: Can 1 or 2 lanes be used without interpolation?

Hey Greg, 

The simple explanation is at lower interpolations more input bandwidth is required at the same DAC update rate. LMFS modes with less lanes cannot have as much input bandwidth due to the lower lane count and therefore it is not practical/possible to both have low interpolation as well as only use 2 or 1 lane. 

In theory, one could run the DAC at a low enough update rate to allow 1x interpolation over 1 or 2 SERDES lanes; however this is not supported by the device. In that case one could run the DAC at a faster update rate and use interpolation to bring the SERDES rate down.

Matt

Hello Matthew,

When you say "not practical" or "not supported", are you saying there is a specific hardware limitation, or simply that it would be an odd use case?  In my application, I am primarily concerned with analog channel density and settling time. I'm aware that the DAC sample rate must necessarily be reduced to accommodate the reduced data rates.

Hi Matthew,

Thanks for the clarification. For now, I'll plan on using 4 lanes per device.

No problem Greg. These devices are quite particular about these types of things. I'm just curious, can you not use interpolation due to the interpolation filter bandwidth? 

It's more that my application is a bit unconventional, and I care more about minimizing settling time of the DAC outputs than a clean frequency response. I won't even be using a reconstruction filter of any kind, and just using the unfiltered zero-order-hold behavior of the DAC.  Enabling interpolation would cause long ringing transients after a step change in the signal, which would be very detrimental in my use case.

Greg, 

That makes sense. Appreciate the insight. I'll feed this back to systems so in the future we can try to support these types of modes. 

Matt