DAC38RF82: Interpolation Filter Bandwidth

Jonathan Kolbrak

Part Number: DAC38RF82

I'm trying to understand how to calculate which interpolation rate is acceptable for my application. I have one channel 20 MHz wide that I'm upconverting to 2 GHz. The datasheet says that the FIR filters are designed with a passband BW of 0.4xfinput. If Fsample = 6.4 GHz. So I'm not clear what the finput refers to and how to calculate the useable bandwidth of the interpolation filters. Example if the interpolation was 8 what is the bandwidth of that filter and would it pass the 20MHz needed for this signal.

over 6 years ago

0 Brian2001 over 6 years ago

TI__Intellectual 2750 points

Jonathan,
I have forwarded your question to an engineer that can help.
Regards,
Brian

0 jim s over 6 years ago in reply to Brian2001

TI__Guru* 91947 points

Jonathan,

To get 20MHz of bandwidth, you will need a data rate of at least 50MHz (50MHz x .4 = 20MHz).If you want to up convert to 2GHz, you could interpolate by 8 and easily meet this requirement. The question is, how fast can you provide data to the DAC. With the interpolation factor of 8, you would need to provide data to the DAC at 250MHz. This frequency and the BW you plan on using will determine the required interpolation rate. Attached is an app note with more information that may be of help.

Regards,

Jim

DAC App Note.pdf

0 Jonathan Kolbrak over 6 years ago in reply to jim s

Intellectual 460 points

Thanks Jim,

So I have a follow up question. If I set things up as you described, which was very helpful, and configure the JESD bus in 42111 mode it seems that the lane rate would be 1.25 GHz. However if I use the DAC38RF82 eval software in simulation mode and set it up similarly it says the current serdes lane rate is 8 GHz? I'm wondering if I just don't have something set up correctly or is that the max rate?

0 jim s over 6 years ago in reply to Jonathan Kolbrak

TI__Guru* 91947 points

Jonathan,

Can you send the screen shot of the GUI that shows this lane rate of 8GHz? See if the attached document helps explain the serdes lane rate calculation.

Regards,

Jim

4571.DAC Line rate calculation.pptx

0 Jonathan Kolbrak over 6 years ago in reply to jim s

Intellectual 460 points

Jin,

Thanks for the info. Here is what I was seeing from the eval software.

I'll work through your ppt and see where things differ.

Thanks,

Jonathan

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DAC38RF82: Interpolation Filter Bandwidth