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Measurements >> Phase Noise and Jitter Measurements >> Relationship between PPM & Jitter
https://designers-guide.org/forum/YaBB.pl?num=1277819927

Message started by gavin on Jun 29^th, 2010, 6:58am

Title: Relationship between PPM & Jitter
Post by gavin on Jun 29^th, 2010, 6:58am

I've been searching on the internet for a while but cannot find a good article outlining the difference/relationship between jitter and PPM.

Can anyone explain to me the difference/relationship between jitter & PPM?

In what application would PPM be of most concern? In what application is jitter of most concern?

Thanks,
Gavin

Title: Re: Relationship between PPM & Jitter
Post by Ken Kundert on Jun 30^th, 2010, 12:04am

PPM?

Title: Re: Relationship between PPM & Jitter
Post by Mayank on Jun 30^th, 2010, 1:30am

Parts Per Million (PPM) is a unit for relative measurement.

1e6 parts per million = 100%.
100 parts per million = 0.01%.

OR

1% = 10,000 PPM

Hence a rms jitter of 1% of the Time Period is equivalent to 10,000 PPM.

--
Mayank.

Title: Re: Relationship between PPM & Jitter
Post by gavin on Jun 30^th, 2010, 8:06am

I guess I should be clearer, what I'm looking for is the relationship between Oscillator Tolerance (typically specified in PPM) and Jitter.

Title: Re: Relationship between PPM & Jitter
Post by gavin on Jun 30^th, 2010, 8:38am

I've been doing some more research and here's what I found.

When dealing with Jitter and Tolerance I'm looking at oscillator stability.

Stability can be broken down into 3 categories:
1/ Long Term Stability eg) greater than 1 day
2/ Short Term Stability eg) 1s to 1 day
3/ Very Short Term Stability (or Phase Noise) eg) less than 1s

Tolerance would fall into categories 1 & 2 whereas Jitter would fall into category 3.

So basically they I am measuring different specs of an oscillator when I measure Jitter and when I measure tolerance.

Any thoughts?

-Gavin

Title: Re: Relationship between PPM & Jitter
Post by Ken Kundert on Jun 30^th, 2010, 9:20am

I am not familiar with Oscillator Tolerance. Tolerance to what?

I am also not seeing a clearly defined question. Perhaps you can further clarify what you are looking for.

-Ken

Title: Re: Relationship between PPM & Jitter
Post by gavin on Jun 30^th, 2010, 9:53am

Ken Kundert wrote on Jun 30^th, 2010, 9:20am:

I am not familiar with Oscillator Tolerance. Tolerance to what?

Crystal oscillators typically specify a nominal frequency as well as a "tolerance" about that nominal frequency since no oscillator can output a single frequency perfectly. For example, if I want to buy a 25MHz oscillator I will find the manufacturer might have 25MHz +/- 50PPM while another might have +/- 1PPM (at a higher cost of course). The 50PPM and 1PPM is what is called the tolerance of the oscillator.

Ken Kundert wrote on Jun 30^th, 2010, 9:20am:

I am also not seeing a clearly defined question. Perhaps you can further clarify what you are looking for.

What I was trying to understand was the relationship (if any) between the Jitter specification (typically provided in ps rms in the digital world) of an oscillator and the Tolerance specification (typically measured in PPM or parts per million).

My second post was some things I found searching on the internet which somewhat answered my question - they are measuring two different things. But, not being an expert I was looking to see others thought.

-Gavin

Title: Re: Relationship between PPM & Jitter
Post by hyy95 on Jun 30^th, 2010, 3:25pm

Tolerance is the character of the crystal, it tells you how precise the manufacture cut the crystal, it's like process variation.

Jitter is the attribute of the oscillator circuit, it relates to phase noise.

That's my understanding, i maybe wrong.

Title: Re: Relationship between PPM & Jitter
Post by love_analog on Jul 29^th, 2010, 7:31am

Gavin
There is no correlation between ppm and jitter. The former is more of a dc quantity (if you may), the latter is more of phase noise at a given point of time.