Topic: FMC150 VCO Lock Problem  (Read 5856 times)

slacheta December 31, 2012, 08:42 AM

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   I have one problem with CDCE72010. I am setting
 divider's M=625, N=384, P=8, R=1 i.e. Register10 = 05FC270A,
 Register11 = 0000040B. Now if I am changing M value to 624 or N value
 to 385 i.e.  Register10 = 05FC26FA or Register10 = 0600270A then PLL
 of CDCE is not locking..........why ? What is the range of VCO ?
 Because i want to generate 512 MHz from VCO so that i can get exact 32
 MHz frequency at output.........what should be the probable solution ?
  • « Last Edit: January 02, 2013, 10:16 AM by peter »

peter January 02, 2013, 10:15 AM (#1)

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Hallo Santosh,

The CEDE72010 uses an external VCO. I assume you are working with a standard FMC150 configuration, in which the VCO has a frequency of 491.52MHz with a typical Kv of 445ppm/V. A frequency of 512MHz is out of its range.
You could used an external clock or contact for a custom VCO option.



slacheta January 03, 2013, 05:17 AM (#2)

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Hello Peter,

Since last month I am  doing alot of experiment on harware and
I am using Avnet's reference design, I have noted two points while verifying it on hardware,

(1) If I am providing external loop back i.e. from  DAC to ADC, then at the output of DDC we should get a perfect sinusoid, But I am not able to get it, and I have checked output of DAC on oscilloscope that is a perfect sinusoid, Why it is so ?  and I have followed all the steps correctly.
Now, If I am providing single channel feedback then at the output of DDC I am getting perfect sinusoid on both the channel,,,,,,,,Why.....?

(2)  Now if I am giving 10 MHz external signal from signal generator to the ADC and  I have bypassed it directly to the DAC ,So it should give same signal at the output But it is not happening, Why ?
(sampling rate of ADC is 61.44 MHz ) and f I am giving 30.72 MHz external signal from signal generator to the ADC then it is showing me appox. same signal,,,,,,,,,,I am not getting that Why  ? it is happening.

ebarhorst January 04, 2013, 06:42 AM (#3)

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Hi Santosh,

we're not aware of the specificities of the Avnet reference design and I advise you contact Avnet in that regard.

Best regards,

  • « Last Edit: January 04, 2013, 01:54 PM by peter »