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Meeting Bandwidth requirements with AD916X/AD917X

Hi,

We are evaluating AD916X and AD917X for our application, here following are the requirements of our application

  1. To have an Instantaneous Baseband Bandwidth of 1200 MHz (centered at 0)
  2. Use DAC Sampling rate (FDAC) of about 8000 MSPS
  3. Use 2x or 4x interpolation in order to have easier onboard analogs, effective DAC Data rate (FDATA) will be 4000 MSPS or 2000 MSPS respectively
  4. DAC LO frequency needs to be around 2500 MHz

Following are our doubts

  1. As per AD916X and AD917X datasheets, using any Interpolator limits the Usable Bandwidth, suppose if we are interpolating by 4x, then Usable BW = 80% of FDATA/2 = 800 MHz. Is it correct? Is there any way to use it for 1200 MHz Bandwidth?
  2. In the case of AD916X, with FDAC = 8000 MSPS interpolation by 2x cannot be used as this will make the FDATA = 4000 MSPS, this FDATA is not supported for Complex data as per Note 2 under Table 35, is it correct?
  3. If we use 2x FIR85 in AD916X and send the 1200 MHz Bandwidth Baseband samples centered @ 0 Hz @ FDATA = 2000 MSPS, and if we mix it with a LO; then at the output of the DAC, LO to LO+600 MHz will contain (DC to +600MHz) baseband spectrum and its mirror image on LO-600MHz to LO, is it correct? An EZ gives a GIST on it: https://ez.analog.com/data_converters/high-speed_dacs/f/q-a/22481/ad9162-with-ads7-how-to-achieve-dc-to-6-ghz-in-2x-nrz-mode
  4. Do you suggest any DACs among AD916X, AD917X, or any other DACs to meet our requirements?

Thanks,

Kiran

  • Hi,

    After going through the AD9174 Datasheet, with the following configurations

    • Main interpolation factor set to 4x
    • FDAC = 8000 MSPS
    • FDATA = 2000 MSPS
    • Each JESD204B Line working at 10 Gbps (2 G * 32 b = 64 Gbps; Lane rate = (64/8)*1.25 = 10 Gbps)
    • Using in Single Link Mode
    1. With this configuration, As per Table 35 in the AD9174 datasheet, Usable Bandwidth = 0.8*FDATA = 1600 MHz (-800 MHz to +800 MHz as per Figure 70), this should be able to meet our requirements mentioned in the original post, is it correct?
    2. If it's correct and if we can move ahead, then as per Table 13 in AD9174 datasheet (Our closest match would be Wideband Modes -> 3000 MHz -> (N = 16 Bits) Complex), Our JESD204B Modes Shall be either 10 or 11, Is our understanding correct?
    3. Here again, with this JESD204B Mode as per Table 17/18, M0S0, M0S1 corresponds to In phase data (I) Sample 0 and Sample 1 respectively and M1S0, M1S1 corresponds to Quadrature phase data (Q), is that right?

    Please provide your valuable feedback.

    Thanks,

    Kiran

  • Hi Kiran,

    This makes sense. Please note that the Fdata with interp>1 implies I/Q samples. So Fdata is the data rate per I or Q. The combined IQ datarate would be Fdata * M, where M is the number of data streams ("number of DACs" in the JESD204 spec). For a single I/Q channel M=2.

    Fdata is also the symbol rate for a QPSK signal (ignoring FEC and other overhead). 

    Fdata * 2/8 * 16 * 10/8 = Fdata * 5 = 10Gbps (also matches your answer, but I wasn't clear on where the "32" factor came from in your calculation)

    In the order of the questions in the latest post: 

    1. iBW= 1600MHz is correct. the iBW we list is the combined IQ BW. meaning this covers both sidebands, -800MHz to 800MHz as you mentioned. You also mentioned you need "an Instantaneous Baseband Bandwidth of 1200 MHz (centered at 0)". So would you need +/- 1200MHz or is +/- 800MHz enough?

    2. Yes - you would match the L, M, NP used to calculate the lanerate to the modes listed in Tables 15:

    3. yes. In terms of the link, each "M" represents a datastream. so an I/Q pair would have two streams, M=2, with M0 corresponding to [I] and M1 corresponding to [Q] (it may be the reverse: M0==[Q] and M1==[I]. You could derive this experimentally, if this is critical to know, by looking at which sideband gets canceled at the output, e.g.). 

    Please let me know if you have any questions on this. 

    Landsman

  • Hi ,

    Thank you for the reply and for answering the latest post, It would be helpful if you please provide your views on the Initial post (old post).

    Please note :

    • When we said 1200 MHz (centered at 0), We meant DC+/- 600 MHz.
    • Regarding 32b : MxNP = 2x16 b; or in another way its (16 bit I + 16 bit Q) @ FDATA

    With the Sampling and Bandwidth requirements mentioned in the initial post (Old post, with  4x interpolation), will we be able to meet our requirements of processing (DC +/- 600 MHz) Bandwidth and Mix it with LO @ around 2.5 GHz using AD9162 or AD9164?

    Thanks again for Replying,
    Kiran

    1. As per AD916X and AD917X datasheets, using any Interpolator limits the Usable Bandwidth, suppose if we are interpolating by 4x, then Usable BW = 80% of FDATA/2 = 800 MHz. Is it correct? Is there any way to use it for 1200 MHz Bandwidth?
      1. [AL] The interpolation filter covers a BW that is equal to 80% of the JESD204B link datarate. The BW is not programable. Generally, Fdata = Fdac/interpolation. 
    2. In the case of AD916X, with FDAC = 8000 MSPS interpolation by 2x cannot be used as this will make the FDATA = 4000 MSPS, this FDATA is not supported for Complex data as per Note 2 under Table 35, is it correct?
      1. [AL] AD916x has the FIR85 filter which allows clocking the DAC core at twice the input clock rate. This is true for AD9164 and AD9166, although the datasheets describe this slightly differently. See 2xNRZ. For Fdac=8GSPS, Fclk = 4GHz with FIR85 enabled. Then, Fdata=Fclk/interpolation. 
      2. [AL] the max datarate is limited by the max JESD204B SERDES lanerate. AD916x cannot run the link at 4GSPS because its lanerate is limited to 12.5Gbps.    
    3. If we use 2x FIR85 in AD916X and send the 1200 MHz Bandwidth Baseband samples centered @ 0 Hz @ FDATA = 2000 MSPS, and if we mix it with a LO; then at the output of the DAC, LO to LO+600 MHz will contain (DC to +600MHz) baseband spectrum and its mirror image on LO-600MHz to LO, is it correct? An EZ gives a GIST on it: https://ez.analog.com/data_converters/high-speed_dacs/f/q-a/22481/ad9162-with-ads7-how-to-achieve-dc-to-6-ghz-in-2x-nrz-mode
      1. [AL] The NCO+interpolation blocks form a digital upconverter. At basedband the lower sideband is imaginary. once upconverter, it may become visible depending on how the I/Q data was generated: either to eliminate a sideband, or transmit on both sidebands. 
    4. Do you suggest any DACs among AD916X, AD917X, or any other DACs to meet our requirements?
      1. [AL] either device could be used, depending on price and auxiliary features needed (PA protection, channelizers, built-in clock PLL, etc). AD9164 is an earlier model, which has superior phase noise. AD9166 has an additional output stage to enhance the frequency response to 8GHz and beyond (albeit increasing IMD3 and harmonics, but maintaining the phase noise performance). AD917x is a dual-DAC, with a simpler power supply design; it consumes less power, and can cover a wider analog BW, beyond 5-6GHz with proper PCB design. So the answer depends on what you are specifically looking for, as a system designer. You may reach privately to our Field team if you would rather have a more detailed discussion about your application  
  • Hi

    Thanks for the response and clearing our doubts, we will further check with the Field team; however, before closing this Q&A, it would be helpful if you could answer this one last query.

    If we use 8 GHz as FDAC/FCLK, 4x as main interpolation factor, No channel interpolation, FDATA = 2 GSPS, JESD in Mode10/11 with each lane working @ 10 Gbps, Baseband IQ data corresponding to 1200 MHz (DC +/- 600 MHz) Bandwidth and DAC LO @ 3 GHz as per the sample diagram below 

    Here Please note that the baseband can have Valid and Non-mirrored information from -600 MHz to +600 MHz, suppose if we use AD9164 or AD9162 will the HB filter (4x interpolation) be able to handle this Bandwidth? and also will there any issues in getting the Required DAC Output Spectrum as per the diagram above?    

    Thanks,
    Kiran

  • Hi , could you please provide your feedback on the above query.

    Thanks,

    Kiran

  • Hi Kiran,

    Thank you for your interest. Yes, you could use the AD916x to the same effect. it supports iBW up to 2.25GHz. I would suggest to set it  in either mix-mode (green, below) or 2xNRZ (red). 

    The explanations in the AD9162 and AD9166 datasheets are slightly different (the AD9166 was released more recently) but it refers to the same mechanism.  

    Frequency response would depend on both Fclk and output mode:

    mix mode would consume less power compared to 2xNRZ.

    Overall, AD917x would have better response at higher frequencies and can support higher datarates. But the AD916x, typically, would have better AC specs, and in particular Phase noise. 

    Landsman