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DAC34SH84: about Near spurious noise

Part Number: DAC34SH84

Hi all,

My customer would like to know the performance of near spurious noise of DAC34SH84.
Their test results of 184.32MHz +/-62.5kHz was about -62dBc/100kHz. DACCLK was 732.78MHz and its phase noise at 62.5kHz is  -126dBc/Hz.
And the test result was lower than their expectation. 

Could you please share the data of spurious noise level at 184.32MHz +/-62.5 kHz and its waveform?
 
The test condition is as follows;

  1. DAC_CLK frequency: 737.28MHz (PLL disabled), Interpolation: x2
  2. DAC_output frequency: 184.32MHz (single tone)
  3. 0-dBFS digital input, 20-mA full-scale output current with 4:1 transformer    

Regards,
Toshi

 

  • Hey Toshi,

    I may be misunderstanding you but is this what you are asking for?

    The noise floor is -90 dBc at +/- 62.5kHz offset.

    Yusuf

  • Hi Yusuf-san,
    Thanks for quick response.

    There are some questions as below;

    1.Looking at the received data, it is -90 dBc / 300 Hz (VBW setting is 300 Hz), so if converted to dBc/100kHz it will be -64.7 dBc/100 kHz.
        Is my understanding correct?

    2. Is this output waveform from the NCU of DAC?
        I am sorry  I did not explain this in advance.

    3. What is the frequency setting of fdacclk and fdata?  I would like to confirm whether it was the same condition with customer's setting or not.

    4. What is the phase noise capability of DACCLK_P/N at ± 62.5 kHz?

    5. Is this waveform the best performance?

          Under the Radio Law, unnecessary launches of ± 62.5 kHz offset from the carrier center frequency are specified to be less than -60 dBc/100 kHz.
           If -64.7 dBc/100 kHz is a real value, there is only a several dB margin.

    6. Please tell me if there is a measure to reduce this neighboring noise by register settings and etc.
     Their DAC output performance measurement result is about -62 dBc/100 kHz which is almost same as your measurement result.

    Thanks and regards,
    Toshi

  • Hey Toshi,

    See that the resolution and video bandwidth are set to 300 Hz. There measurement is -90dBc/300Hz or approximately -113dBc/Hz to simplify. Now adding 30 dB to make it /kHz we get approximately -83dBc/kHz which meets the spec.

    Hopefully this helps.

    Yusuf
  • Hi Yusuf-san,
    thanks for your reply.
    I understood your explanation.

    Would you please reply to the remaining questions (No. 2 thru No.6)?

    Thanks and regards,
    Toshi
  •  2. if by "NCU" you mean "NCO" then no. I did not use the NCO. The input frequency to the DAC is 183 Mhz.

    3. I used the settings you suggested. Fdac = 737 MHz, Int = 2, Fdata rate = 368.64Mhz

    4. Reference waveform

    5. Yes this is good performance. You can reference the NSD graph in the data sheet for best performance.

    Yusuf