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how to use dynamic phase shift

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Observer
Posts: 46
Registered: ‎08-26-2013
Accepted Solution

how to use dynamic phase shift

I use vivado 2014.4,Kintex 7 325T,and I want to dynamic change the clock output phase,and I assert the PSEN and PSINCDEC,after some clock periods,the mmcm assert the PSDONE,but I compare the clock_in with clock_out,the phase does not change any.do someone know why? and what should I do

Accepted Solutions
Historian
Posts: 4,250
Registered: ‎01-23-2009

Re: how to use dynamic phase shift

There are a couple of possibilities...

 

First, the PSEN/PSINCDEC/PSDONE interface control the dynamic phase shifter in the MMCM. When you configure the MMCM, you select which (if any) of the outputs are connected to the dynamic phase shifter - it is selectable on an output by output basis. So if you are comparing the input to an output that does not use the dynamic phase shifter (or fine phase shifter) then obviously you won't see any difference.

 

The next question is how are you looking at the inputs and outputs? In simulation? On a board with an oscilloscope? With a Vivado ILA (hopefully not)?

 

A single shift on the DPS is 1/56th of the period of the VCO. The VCO is usually running around 1GHz, so a single shift will be around 17ps - it can be really hard to see that small a difference...

 

Avrum

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All Replies
Historian
Posts: 4,250
Registered: ‎01-23-2009

Re: how to use dynamic phase shift

There are a couple of possibilities...

 

First, the PSEN/PSINCDEC/PSDONE interface control the dynamic phase shifter in the MMCM. When you configure the MMCM, you select which (if any) of the outputs are connected to the dynamic phase shifter - it is selectable on an output by output basis. So if you are comparing the input to an output that does not use the dynamic phase shifter (or fine phase shifter) then obviously you won't see any difference.

 

The next question is how are you looking at the inputs and outputs? In simulation? On a board with an oscilloscope? With a Vivado ILA (hopefully not)?

 

A single shift on the DPS is 1/56th of the period of the VCO. The VCO is usually running around 1GHz, so a single shift will be around 17ps - it can be really hard to see that small a difference...

 

Avrum

Highlighted
Observer
Posts: 46
Registered: ‎08-26-2013

Re: how to use dynamic phase shift

Hi:

 Thanks,my MMCM has just an output ,and I look at the input and output with ISIM in simulation,and Fclkin is 125M ,VCO is 1G .I think,at the time of generating the core,if there some things I ignored