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Frank Wiedmann Community Fellow Offline Posts: 678 Munich, Germany	Re: Simulation of DJ using SpectreRF Reply #15 - Jan 13^th, 2020, 12:48am Select the node of which you want to analyze the performance. Usually, that's probably the output node.
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dnw

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Posts: 26

Re: Simulation of DJ using SpectreRF
Reply #16 - Feb 13^th, 2020, 1:59pm

Hi Frank,
I am trying to setup a ring oscillator followed by a driver for supply senstivity analysis.
Both oscillator and driver share the same supply.
If I give 10mVp(20mVpp) 5MHz ripple on the supply then in transients sim I see a variation of 150fs peak(300fspeak-peak around 370ps nominal)
I tried replicating the same with pss + pxf analysis based on your previous posts
So in pss I choose the following
Enginer: Shooting
Beat Freq : fosc(1/370p)
output harmonics(No of harmonics) : 20
Oscillator: ticked
case1:
Osc Node+ : Driver out
Osc Node- : gnd

case2:
Osc Node+ : Terminal inside ring oscillator
Osc Node- : gnd

Pxf settings
sweeptype: default
Relative harmonic: 0
Freq sweep : 10Hz - 200MHz
Sidebands: Max sidebands: 1
case1:
Pos output node : Driver out
Neg output node : gnd

case2:
Pos output node : Terminal inside ring oscillator
Neg output node : gnd

Threshold = Vdd/2

Max Samples (Have tried blank and 2000 getting the same results with both)

I am trying to interpret the results I get out of these sims. As mentioned above I have two sims with pxf
case 1: one with a output of final driver selected for pss and pxf
case 2: one with a node inside the ring oscillator selected for pss and pxf

I am measuring the voltage gain @ 5MHz offset from the oscillation frequency
I get different gains for both cases
case 1: Gain of 6.5V/V
case 2: Gain of 10V/V

Even if one of them is right with 30GV/s dv/dt I get peak dt of 3.3ps with 10mVp which is almost 20 times more than what I am measuring with transient.
Could you please help me in figuring out where I am getting this wrong.

Thanks & Regards

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« Last Edit: Feb 14^th, 2020, 8:18am by dnw »

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Frank Wiedmann Community Fellow Offline Posts: 678 Munich, Germany	Re: Simulation of DJ using SpectreRF Reply #17 - Feb 14^th, 2020, 4:24am The PXF frequency is the frequency of the power supply ripple, so you should look at the result at 5MHz (which isn't even inside your sweep range right now).
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dnw Junior Member Offline Posts: 26	Re: Simulation of DJ using SpectreRF Reply #18 - Feb 14^th, 2020, 6:48am Hi Frank, Sorry for the confusion i am sweeping from 10Hz - 200MHz I looked at 5MHz the gain is even higher 50 Which also does not look right. Thanks
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Frank Wiedmann

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Posts: 678
Munich, Germany

Re: Simulation of DJ using SpectreRF
Reply #19 - Feb 14^th, 2020, 8:52am

I don't see any obvious problem with your setup. This has worked for me pretty well in the past, but I have not run this kind of analysis for quite some time and I also did not run it on oscillators back then. I suggest that you contact Cadence Support to let them sort this out, other people are currently also having problems with this kind of analysis (see https://community.cadence.com/cadence_technology_forums/f/custom-ic-design/43477...).

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dnw

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Re: Simulation of DJ using SpectreRF
Reply #20 - Feb 14^th, 2020, 10:23am

Thanks, Frank I will try following up with them
Also, I was reading PSRR_OSC_AN.pdf from the spectreRF Workshop folder.
There they suggest using modulated instead of sampled for power supply sensitivity analysis. Just trying to understand the difference.
Thinking about this I think any perturbation on the power supply is kind of causing phase modulation around oscillation freq.

Thanks

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