It is one way to do it.Is this the best way to do it?
The circuit mainly depends on the used XTAL. It´s datasheet tells you how to use it.What is the formula used to calculate C, R1, and R2 for a 40 Mhz crystal?
Thank you. That was very helpful. The original circuit has been copied from:The standard CMOS crystal oscillator uses an unbuffered inverter rather than ST gate. The author also makes his life easy by not specifying the logic family. If the circuit should work with ST gates, very unlikely at 40 MHz.
I'd rather trust manufacturer application notes like below quoted from Epson.
View attachment 178685
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Where did you copy the post #1 schematic? I guess it has been edited by someone who doesn't understand circuit oscillation condition.
Thank you!Hi,
It is one way to do it.
We can´t say if it´s the "best" because "best" - without saying in which regard - is meaningless.
It could be the "best" reagrding: cost, size, availability, current consumption, jitter, temperature stability ..... and many other.
The circuit mainly depends on the used XTAL. It´s datasheet tells you how to use it.
Usually the manufacturer provides additional information like application notes, design notes, example circuits, online calculators... and so on.
--> Thus visit the website and look for information.
Klaus
Thank you Dana. That was an interesting read!This might help -
Regards, Dana.
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40 Mhz will require some very fast G elements :
Above << 10 nS Tpd. Not sure of their gain.....
Regards, Dana.
Right. I have several circuits/implementations that all use an inverter. However, I don't know why they used schmitt inverter on this one. Anyways, most implementations I come across use two inverter stages.I don't think you want a Schmitt inverter. All the CMOS XOs
I've seen, seem to want single stage inverters with no
hysteresis.
No, not relatively that large number. Do you have any reference for these modules, datasheet, PN, etc.Unless you are requiring large numbers of the oscillator circuit it is always better to buy a oscillator module particularly if the frequency required is above 8Mhz or so.
There are hundreds of different ST32 .... We don´t know which one you refer to.of MCO pin in the STM32. And in case of the latter, is there any need for inverter, amplification, or caps?
Klaus,Hi,
did you try an internet search "xtal oscillator" on your own?
There are hundreds of different ST32 .... We don´t know which one you refer to.
Each one comes with a datasheet.
But even if we knew the exact type, it´s important that you read the datasheet first.
There usually is a whole section about the clock input.
Klaus
Yes, my mistake. I wrote "input" while I meant the complete oscillator circuit. Yes, I am not perfect and never wrote and never meant it to be.I really didn't ask about the clock input of my MCU
So there exactly are two questions in your intial post:Please refer to the OP and read it carefully before you reply. You always take a portion of my input, reply it, and ignore the main issue.
No, not relatively that large number. Do you have any reference for these modules, datasheet, PN, etc.
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By the way, what is the difference between supplying the clock (16~40 Mhz)from the above crystal oscillator circuit vs the output of MCO pin in the STM32. And in case of the latter, is there any need for inverter, amplification, or caps?
Thank you very much. That's exactly what I wanted to know, and that's exactly what I call a very helpful reply.Compared to a crystal oscillator, jitter of STM32 PLL is large and potentially unsuitable for applications that need a clean clock source, e.g. RF communication or signal generators but sufficient for most general digital purposes.
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MCO pin shares GPIO static and dynamic specifications, in so far the datasheet leaves no open questions.
Thank you Dana. That was very helpful, too! So, basically for lower frequencies, jitter is minimal.Confirm this sure looks like it falls under GPIO specs, and jitter measured :
View attachment 178743
Signal digital generators at 100 Mhz around 200+ ps, Rigol stuff. DDS based arbitrary type.
Regards, Dana.
Klaus,Hi,
fair enough.
Yes, my mistake. I wrote "input" while I meant the complete oscillator circuit. Yes, I am not perfect and never wrote and never meant it to be.
All the rest of my post exactly refers to your problem.
It´s still a question of thechnical specification of the one IC´s output and the other´s IC´s input.
Still my way is to read the datasheets. (we still don´t have any information of both involved ICs. Not our fault.)
It´s my way to read datasheets. I do it every day. If you have a better way, then please tell us. I still want to learn.
So there exactly are two questions in your intial post:
* About the "best"
Without knowing what the "best" is for you .. the question can not be answered. I asked questions about your "best" requirements but you did not answer them.
* about the formula:
I gave you the exact way that I learned to use in my several decades of electronics development experience.
Nobody is able to give you a more detailed answer because - again - you missed to give detailed information.
I don´t tell stories, if I need detailed information I do it exactly like written. Why should I recommend you a different way?
And still: It´s just a recommendation. It´s on you whether you use this or not.
Until now we don´t know what XTAL you use, what supply voltage you use, what "legacy device" you want to supply and so on. All things that need to be considered. No story, just fact.
So in my opinion I used every single information you gave to support you with the best available answer.
***
If you miss to give clear informations, then please don´t blame it on others.
Missing technical informations, missing datasheet links, missing links to websites, missing to tell "what homework you did" ....
If you can´t stand to be asked for "doing an internet research" ... then please tell us that you did, what you expected to find and what you missed to find.
If you think asking for information is a bad thing, then what did you do on post#1?
Or .. are you allowed and we not? Master - servant?
If you jump form one topic ("best" and "formula" of the given XTAL oscillator) to another within a thread ... again: don´t blame it on us.
I´m not perfect. I know.
Maybe you are perfect. I also don´t know.
Klaus
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