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Explorer
Explorer
1,106 Views
Registered: ‎05-07-2012

Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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Hi,

 

I've implemented a Ring Oscillator using three IDELAY2 primitives and an inverter  in a Vivado Zynq7000 project.  I implemented it and have a test bench to exercise the implementation in post-implementation functional and then timing simulations.  So, the output of the oscillator is a red flat line in both cases on the simulation waveform file.  That is, it is not oscillating.  So, I'm wondering if anyone has any ideas why this simulation isn't oscillating like I would like?  Should the simulator be able to capture something like this?

 

Thanks.

 

 

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Scholar jmcclusk
Scholar
1,705 Views
Registered: ‎02-24-2014

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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Add a reset signal to your ring.. Instead of an inverter, make it an NOR gate, and apply a reset pulse of 50 ns to the other input of the NOR gate to force the ring low.   Then once the reset pulse disappears, you should see an oscillation.

Don't forget to close a thread when possible by accepting a post as a solution.
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Scholar austin
Scholar
1,104 Views
Registered: ‎02-27-2008

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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How do you start the ring oscillating in your test bench?

Austin Lesea
Principal Engineer
Xilinx San Jose
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Scholar jmcclusk
Scholar
1,706 Views
Registered: ‎02-24-2014

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

Jump to solution

Add a reset signal to your ring.. Instead of an inverter, make it an NOR gate, and apply a reset pulse of 50 ns to the other input of the NOR gate to force the ring low.   Then once the reset pulse disappears, you should see an oscillation.

Don't forget to close a thread when possible by accepting a post as a solution.
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Explorer
Explorer
1,089 Views
Registered: ‎05-07-2012

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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Thank you.  

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Scholar ronnywebers
Scholar
990 Views
Registered: ‎10-10-2014

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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just out of curiosity : what is the typical/possible use of a ring oscillator in FPGA

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Scholar austin
Scholar
986 Views
Registered: ‎02-27-2008

Re: Simulation of a Zynq7000 IDELAY2 based Ring Oscillator in Vivado

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rw,

 

Ring oscillators may be used as a clock for logic if all other clocks fail.  One does have to determine the Fmax, and probably just divide it by two before using it and constraining the period to perhaps 40% of the fastest expected just to be safe in timing (over process, voltage, temperature).

 

We use rings to determine speed grade, if we meet our specifications in test.

 

They get used as physically uncloneable functions - PUF.

 

They get used as thermometers, to measure voltage (once calibrated).

Austin Lesea
Principal Engineer
Xilinx San Jose