AD9082 : specification clarification

Dear all,

Reading the datasheet I am unsure of my understanding : what is the maximum sampling rate of a single ADC ?

It is unclear (to me) whether it is 3 or 6 Gsps ?

The same question would hold for the AD9081 : 1.5 or 4Gsps ?

Also, can it support baseband I/Q operation at the ADC input and DAC output ? In such a mode, is it possible to use the DUC/DDC ?

What does observation Rx mean ? I suppose it is intended for channel feedback loop (DPD, equalization, etc...) but how does it translates ? How does it affect my design if I want to use the ADCs as  independent input channels ?

Yann

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    •  Analog Employees 
    on Sep 19, 2019 4:06 PM

    Hello,

    Answers to you questions are as follows:

    1) AD9082 has two ADC's with max 6 GSPS operation while the AD9081 has four ADC with max 4 GSPS operation.
    2) The AD9081 and AD9082 can be configured for complex inputs/output applications as is the case for "zero-IF" or "complex-IF" applications where a quadrature demodulator/modulator is used to interface to a dual ADC/DAC.  The DDC/DUC can still be used as would be the case for a "complex-IF" application.

    3) Observation Rx pertains to Transmit Digital Pre-distortion applications where the PA output is fed back to an ADC input (after some attenuation) such that the quality of the transmit signal can be observed with digital pre-distortion coefficients modified to maintain sufficient linearity performance.

    4) ADC's can used as 4 independent channels.  This is the case in direct RF applications where each ADC input would have its own antenna.  In this sort of application the digital data path is also used to down-convert the desired RF bands to a digital zero-IF signal.


    In the case of the AD9081 and AD9082, one can completely bypass the digital data path such that ADC's operate in Nyquist Mode allowing for maximum signal bandwidth capability.   

  • Hi, thanks for the swift reply!

    Based on your reply, the maximum real RF signal sampling rate (per ADC in multichannel mode) is 6Gsps. Hence, a Nyquist zone bandwidth is 3GHz, and I would expect a useful bandwidth around 2.4GHz (0.8*3). The SERDES link seems able to take the maximum throughput as well.

    In the datasheet it is mentioned: "The maximum radio band spacing supported in multichannel mode is 1.2 GHz." This is the bit which confused me... This is just 40% of the full Nyquist zone. I am guessing there is something wrong in my understanding, but I cannot point where I went wrong…

    Thanks again for the support.

  • +1
    •  Analog Employees 
    on Sep 15, 2020 6:06 AM in reply to YANN.M

    1.2GHz multichannel should mean 4 channels DAC with every channel 1.2GHz BW, so the max serdes lane rates would go to 24.75G jesd204c which is the max lane rate of AD908x.

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