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glenaus2
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Registered: ‎09-01-2015

PIXCO settings for XAPP1308 HSYNC Sychronization

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On our existing SDI video products, we are now adding genlock.  This has led me to trying to implement XAPP1308.   I am currently getting the Saturation of the low pass filter integrator and output errors (OVF_INT, OVF_VOLT) and the clock does not appear to be syncing.  See below for my settings and the flagged error and the frequency response estimate for my settings.  Any help troubleshooting this would be appreciated.

 

freq_response.jpg

 

VIO.jpg

 

 

 

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glenaus2
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Registered: ‎09-01-2015

Ok, thanks everyone.  I have it working. Table 1 in XAPP1308 was confusing things, but I needed to tie VSIGCE_O to VSIGCE_I per figure 7.

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glenaus2
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I changed the gain settings to improve the frequency response, but I am still getting the overflows.

 

freq_response2.jpg

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jmcclusk
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Registered: ‎02-24-2014

you are running your phase detector at a really low frequency (13.4 KHz), and your loop bandwidth is comparable..   That's simply not stable..    your phase detector frequency has to be at least 3 or 4 times your loop bandwidth, otherwise your loop will jump around like a crazy monkey.     If I were you,  I'd try to make the divider R as small as possible (ideally 1) and adjust the intermediate frequencies needed for V and the upstream PIXCO.  

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gguasti
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Registered: ‎11-29-2007

hello

assuming that you have implemented the PICXO using the required encrypted tcl code (this ensures the correct timing), there are limitations on the max ppm range you can achieve with the PICXO. If the ppm difference between RXOUTCLK and TXOUTCLK is too high, it is possible that the control will saturate, no matter of the low pass filter you will use.

 

glenaus2
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I am taking the V and R values directly from XAPP1308 table 2 for the 1080p59.94 video stndard. 

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jmcclusk
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Then try increasing G1 and G2 to reduce the bandwidth.  

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glenaus2
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Registered: ‎09-01-2015

I have been playing with that without much success.  I will try that once again.

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glenaus2
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I am using it as packaged component downloded from the APP note, so I assume taht contains any needed TCL scripts.

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glenaus2
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Registered: ‎09-01-2015

Ok, thanks everyone.  I have it working. Table 1 in XAPP1308 was confusing things, but I needed to tie VSIGCE_O to VSIGCE_I per figure 7.

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jfrye_wmi
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Registered: ‎08-19-2019

What is the max ppm difference?

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