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How to simulate the nonlinearity of a relaxation oscillator

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Junior Member level 3
Apr 4, 2007
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cosmosscope eye diagram jitter

I have some questions for help.

1. How to simulate the nonlinearity of a relaxation oscillator.
2. Why some papers use HD2 to descripe the control linearity of a oscillator instead of the THD or HD3.
3. what's the difference between ' .fft , .four '
4. What type of jitter can be measured by eye diagram? Is it cycle-cycle jitter?

Please, hlpe me. Thank you very much.:idea::idea::idea:

eye diagram oscillator

1. suppose you said it's VCO. Give a ramp control voltage, check the output period of oscillator. we can get the gain of VCO, then we will get the nonlinearity.
4. from the eye diagram, I think we can measure the period jitter.


Thank you for reply.
1. I can get the v-f curve,but HD2, HD3 is usually used to descripe the nonlinearity, how can I get the HD2, HD3?
4. From some products, I found the parameter of output jitter is 50psp-p. How can I get it(psp-p) from eye diagram?

Does HD2 means 2nd Harmonic Distortion? I have not used HD2 for nonlinearity description in VCO before.
Does psp-p means ps (peak-to-peak)? I find a picture, maybe it can give some information.

eye diagram

You can get more details about jitter at
"Measuring Jitter in Digital Systems, Application Note 1448-1"


YES. HD2 means 2nd Harmonic Distortion.
Yes, it's period jitter. I find the definition.
'Period jitter is the measurement of a signal, generally a repeating signal, from one edge to another similar repeating edge. Common period measurement tools measure the rising edge of a signal to the next rising edge. After taking
a significant sample of period measurements, the standard deviation and peak values can be resolved:
this statistical information is the period “jitter” in the signal.'
But the question are:
1. How can I use cosmosscope to caculate the time differences between every two rising edge. And then get the standard deviation.

2. As I konw, the DB2 is a DC parameter , How can I get it ?

For help , thank you very much.

In CosmosScope we can use its measurement to get the period of each cycle, then can get the period deviation.


Got it, thank you. I get the period jitter.

But how to simulate the HD2,HD3?
why HD2 is xx dB,
but total harmonic distortion = 73.3390 percent
why the units of the HD2 and THD are different?

Re: How to simulate the nonlinearity of a relaxation oscilla

please fefer to spectreRF guide

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