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663 Views
Registered: ‎03-27-2014

non stable IDELAYE2 simulation

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Hi,

 

I'm trying to simulate my LVDS receiver for a 16bit DDR ADC,

 

the receiver is made of an IBUFDS, an IDELAYE2 and an IDDR for each +/- LVDS pair.

 

 

The delay inserted by the IDELAYE2 object is changing through the simulation run: it starts with a ~600ps value (which is apparently default for 7series) than moves to 4000ps then comes back to 600ps, although I am applying a constant value (0) to all of them, and I also make sure the IDELAYCTRL is declared as locked before checking the data. This is not really a problem but the decoded data is therefore not stable and rubbish

 

 I am not sure what might be causing this behaviour, any guesses?

 

EDIT:

I was using the "VAR_LOAD" opmode, that is, CNTVALUEIN is loaded any time "LD" is '1'

Switching to "FIXED" opmode with a default CNTVALUE fixes the problem

So I might be doing something wrong with my Load interface:

 

  • LD is high for one clock cycle & latches CNTVALUE
  • loading causes IDELAYCTRL to RESET and RST is held for many nanosecs (not sure reseting this guy is needed)
  • The test bench now loads a default CNTVALUE for all IDELAY but the problem is still there
  • The test bench does not check CNTVALUEout (make sure CNTVALUEin was properly latched as expected) 
G.W.,
NIST - Time Frequency metrology
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1 Solution

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1,024 Views
Registered: ‎03-27-2014

Re: non stable IDELAYE2 simulation

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Problem solved

 

my bad, I unintentionally tied 'CE' to '1' as I was probably thinking of 'Clock enable' when I did it, but CE/LD/C are part of the loading interface

 

so the simulation works fine for both FIXED/VAR_LOAD modes of operation

G.W.,
NIST - Time Frequency metrology
0 Kudos
1 Reply
1,025 Views
Registered: ‎03-27-2014

Re: non stable IDELAYE2 simulation

Jump to solution

Problem solved

 

my bad, I unintentionally tied 'CE' to '1' as I was probably thinking of 'Clock enable' when I did it, but CE/LD/C are part of the loading interface

 

so the simulation works fine for both FIXED/VAR_LOAD modes of operation

G.W.,
NIST - Time Frequency metrology
0 Kudos