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ring oscillator frequency variation

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pansoo

pansoo

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ring oscillator sensitive supply

Hi all~

I'll design some ring oscillator frequency about 30MHz.

But I'm afraid, if the frequency will be correct in process.

So, I want to know, how big is the frequency variation of ring oscillator in real process.

Thank you. :D
 

ring oscillator trimming

u need to make corrner analysis of ur oscilator to be sure of the performance of ur oscillator on every corner

khouly
 

the fastest will be on FF and -40C and slowest on SS 175C on TSMC FAB. ring oscillator has quite a big variation, only use it on blocks that are not timing sensitive...
 

If you need a ring oscillator for PLL kind of application go for the fully differential ring oscillator .. they have an innet property of robustness against porcess and supply variations.
 

In my experience, ring oscillator will be varied by a big amout.

For example, typical is 300MHz in a specified controlled volatge.

After mass proudction, we can measure as low as 150MHz and as high as 450MHz.

Therefore, you need to cover process variation in your VCO design.

For your reference.
 

For ring oscillator itself, the output frequency will vary from -40% to +40%, PVT. To assure 30MHz output frequency, you either need calibration-trimming or PLL to lock the frequency
 

i agree with armixic , u need a PLL to control the oscillator

khouly
 

it depends on yr spec.In low cost consumer elec. a vco wo a pll is enough.
 

It is depand on the process you used and you should simulate it under different corner.
 

If you adopt PVT compensation circuits, then the frequency will be controlled in a
acceptable range.
 

As all the previous guys already said, the frequency variation is considerable. It may be even bigger if you use lower supply voltage. The main reason behind it is the delay of a basic cell. This delay is a relatively complex function of different parameters (although, there are simplified models for its calculation), and is very sensitive to process variations.
 

Taking together:

VDD+-10%
Temp -40...105
Process SS ... FF

you will get about 2.5x (250%)

That is the ratio! Form min to max. And is exactly what is critical to control.
 

For better accurate, you can employ RC oscillator.
 

Is there completely integrated RC oscillator?
 

Yes. Cap calibration technic works better.
 

yes you need to use trimming to trim the frequency across corners. But variation across V-T can also be high enough, but atleast you can remove the variation across process by having sufficient trimming.


amarnath
 

Did anyone make a RC oscillator with digital trimming which is stable to less than +-10ppm over temperature and supply?
 

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