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ADC32RF80EVM

user5856712
Prodigy 220 points
Other Parts Discussed in Thread: ADC32RF80EVM, ADC32RF80

Hello,

We refer to the ADC32RF80EVM guide book, the fifth part is about EVM board examples.In this example, ADC channel-1 input frequency is set to 1.96GHz, NCO frequency is 1.9GHz, in software HSDC, ADC Input Target frequency is 1.96GHz as shown in the figure, and the final signal is displayed as 60MHz.But if we use it, we need to collect a pulse whose frequency range is from 0Hz to 500MHz or higher, and we don't know ADC Input Target frequency in advance, that is, to sample an unknown signal without using down-mixing sampling mode.How should we set NCO and ADC Input Target frequency and NCO in ADC configuration?This example feels like knowing the frequency of the signal ahead of time and entering it into the HSDC software to get the result.Is my understanding correct?

Best regards,

David

  • 0
    TI__Mastermind 18095 points

    You are interested in capturing 500 MHz of BW.  To do that, you will need a data rate to support that BW.  You need a data rate of 737.28 MSPS with a decimation of 4.  That combination yields a BW of 737.28 / 4 * 80% = 600 MHz which is suitable to capture the desired BW.  Reference table 15 in the datasheet which highlights the various options for decimation rates and LMFS settings.

    In the tool, the sample rate is still 2949.12 MSPS.  The decimation is set to 4.  The NCO is set at the mid-point of the desired band: 300 MHz.  The input frequency is arbitrary.  You can put in a place-holder value. During a capture, the tool will place the marker on the highest tone regardless of the specified input frequency.

    Note, the 'RF80 is set-up with 2nd Nyquist zone transformers by default.  They are outside the datasheet frequency limits at the lower 1st Nyquist frequencies.  Further, the transformers do not pass DC levels.  You may need to consider modifying the board to eliminate the transformers and get direct access to the differential inputs.

    --RJH

  • 0 in reply to RJ Hopper
    Prodigy 220 points

    Thanks,RHJ.

    I have another problem. What is the function of NCO frequency and what can it affect? Does NCO move the active band?As you said, the NCO is set at the mid-point of the desired band: 300 MHz. But  what does NCO mean in this picture？This picture is from ADC32RF80 user guide.

    Best regards,

    David

  • 0 in reply to user5856712
    TI__Mastermind 18095 points

    The NCO is a Numerically Controlled Oscillator.  It is used as a digital mixer.  With data rate set at 737.28 you get about 600 MHz of useable BW that will be centered at the NCO frequency.

    --RJH

  • 0 in reply to RJ Hopper
    Prodigy 220 points

    Thanks!RJH

    But I still have two questions.Both of them are about sampling bandwidth.

    1. We tried to sample a 60MHz signal, and the signal amplitude was the same as in the data manual sample. At this time, set NCO to 0Hz and select sampling rate of 2949.12MHz/8=368.64MHz, but the result is very noisy, low signal-to-noise ratio and the 60MHz signal cannot be distinguished. Why?Is there a problem with our setup?If we want to sample the real frequency directly without mixing, can NCO be set to 0Hz?

    2. We found that for the adc32rf80 configuration, as shown in the figure, only 8 decimation coefficients can be selected, so the bandwidth dsplayed in HSDC is 368.64mhz, which is already the maximum display bandwidth. What should we do if we want more display bandwidth? For example, if you want to display the bandwidth of 1.5GHz, can you adjust the decimation coefficient to 1? The extraction coefficient of 1 cannot be selected now.

    Best regards,

    David

  • 0 in reply to user5856712
    TI__Mastermind 18095 points

    David:  Please see below.  --RJH

    1. We tried to sample a 60MHz signal, and the signal amplitude was the same as in the data manual sample. At this time, set NCO to 0Hz and select sampling rate of 2949.12MHz/8=368.64MHz, but the result is very noisy, low signal-to-noise ratio and the 60MHz signal cannot be distinguished. Why?Is there a problem with our setup?If we want to sample the real frequency directly without mixing, can NCO be set to 0Hz?

    RJH>> The noise is likely from the phase /thermal noise of your input source.  It is best to use a high quality signal generator and filter with a BPF.  If you are truly injecting 60 MHz, note that the input transformers are not rated for that band.  They are likely introducing loss and imbalance which is impacting spurious.

    2. We found that for the adc32rf80 configuration, as shown in the figure, only 8 decimation coefficients can be selected, so the bandwidth dsplayed in HSDC is 368.64mhz, which is already the maximum display bandwidth. What should we do if we want more display bandwidth? For example, if you want to display the bandwidth of 1.5GHz, can you adjust the decimation coefficient to 1? The extraction coefficient of 1 cannot be selected now.

    RJH>> No the 'RF80 does not support decimation by 1 (i.e. DDC bypass) due to export control restrictions.  You are limited to the decimation of 4.  I see that in the pull-down menu.