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AD9172 harmonic distortion issue

Question asked by rampo on Jul 6, 2018

Dear Analog,

we have developed a board with the AD9172 DAC. We are evaluating the harmonic distortion but we see quite bad results compared to the datasheet.

What we see is a third harmonic always quite high even at low frequencies (1Mhz, 10Mhz, 100Mhz) that does not reduce while reducing the signal (sine wave) power.

For example at -12dBFS we get a third harmonic distortion of -63dBc at 100Mhz and about the same at 10Mhz and 1Mhz. We are using the Mode 21 at 6.16Gsps data rate. We use the internal PLL with an external reference clock at 770Mhz.

We use the default current full scale and set the DAC registers as suggested by the ACE software.

We checked all the power supplies and they are in spec. with the datasheet.

We are measuring the harmonic distortion with a Keysight 26.5Ghz CXA spectrum analyzer.

Unfortunately the datasheet has no characterization of harmonic distortion for Mode 21 but in all other modes the 3rd harmonic reported in the datasheet in these conditions (-12dBFS, 10Mhz or 100Mhz) is around -80dBc.

Do you have any suggestion?

Do you have any distortion data for Mode 21?


Best regards, Michele