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Author Topic: Req: Help needed to design a oscillator  (Read 1383 times)
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madhan7710
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« on: June 19, 2012, 12:39:17 12:39 »

Hello,

Am developing a project and the main decoder ic requires 27mhz clock input(not crystal). It operates at 3.3v and that's the maximum VCC.
the problem is i couldnt get a 27mhz oscillator in my area. am able to get 27mhz crystal though. could anyone share a oscillator circuit that works with 27mhz crystal and 3.3v VCC so that i can feed the output directly to the ic.

I searched the net and i could get some 74 and 40 series ic based oscillator but it couldnt take 27mhz crystal directly itseems also VCC is higher.

hope someone must have a solution...

thanks in advance.
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solutions
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« Reply #1 on: June 19, 2012, 02:51:37 14:51 »

http://www.idt.com/document/mk2727-datasheet
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pjmelect
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« Reply #2 on: June 20, 2012, 02:30:36 02:30 »

Quote
I searched the net and i could get some 74 and 40 series ic based oscillator but it couldnt take 27mhz crystal directly

The 74F series can oscillate at 27Mhz with a crystal but the layout is very critical and if not done right can result in the oscillator not starting up or starting up intermittently. Because of this I prefer to use crystal modules at higher frequency's. You could use 74AC or 74ACT at 3.3V if you can find them. Alternatively you could use a transistor but the layout is very critical and it is hard to get reliable start up.     
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krepa
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« Reply #3 on: June 24, 2012, 03:56:06 15:56 »

One transistor and some R/C is OK with you?
Then you can try http://www.rakon.com/Products/Public%20Documents/Whitepapers/SINGLE%20TRANSISTOR%20CRYSTAL%20OSCILLATOR%20CIRCUITS.pdf
There are several circuits which are also explained.
Actually if you need full Vcc swing you need to amplify it so may it's not so good idea.



Posted on: June 24, 2012, 03:41:10 15:41 - Automerged

Another option - if you like SMT is to buy ready made ocsillator http://in.element14.com/jsp/search/browse.jsp?N=2103+204350&Ntk=gensearch&Ntt=27MHz&Ntx=mode+matchallpartial
Maybe you can get also DIP/DIL vesion from other supliers (digikey,...)
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madhan7710
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« Reply #4 on: June 25, 2012, 06:51:54 18:51 »


Thanks for the reply's. At last i ordered the 27mhz module itself as i couldn't get 74hc04 to work properly with 27mhz crystal.
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solutions
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« Reply #5 on: June 25, 2012, 09:46:57 21:46 »

The module you said you couldn't get?

What are you using now?
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madhan7710
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« Reply #6 on: June 26, 2012, 07:25:57 07:25 »


I got a contact of crystal and oscillator manufacturer detail where any custom made frequency is possible but very costly for small quantity. I placed order for 10 Nos there and got it for testing and also ordered a cheaper item in mouser(still didn't reached my hand).

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solutions
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« Reply #7 on: June 26, 2012, 09:22:43 09:22 »

Who, where, and how much for 10? This is not just for me, because I don't need it now. Someone may need it in a search and it'd be nice to have that info available here
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DreamCat
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« Reply #8 on: July 09, 2012, 08:45:35 08:45 »

74HCU??
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May be I expressed the wrong meaning, sorry for my bad english. Please correct it for me if you can.
krepa
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« Reply #9 on: July 10, 2012, 12:45:51 00:45 »

Who, where, and how much for 10? This is not just for me, because I don't need it now. Someone may need it in a search and it'd be nice to have that info available here
One manufacturer from Czech Republic. They can do custom frequencies. It is not cheap but it is possibility.
http://www.krystaly.cz/en/
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Zorktronics
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« Reply #10 on: September 28, 2012, 01:55:35 01:55 »

    Have you done a solution to this problem?

    It's not the easy way, but you can design your own crystal oscillator, i recommend the book: Foundations of oscillator circuit design, from Guilhermo Gonzales, it was helpful when i had to design some Colpitts oscillators, this book is only a start, a lot of nonlinear simulation will be necessary.

    Besides that, you'll need to do spice simulations and get reliable transistor models, maybe you will need to do an amplifier to have the right voltage level to drive your logic buffer.
   
    If you need more specific advice please reply on this topic.

   Good luck!
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