Path: utzoo!mnetor!uunet!tektronix!tekcrl!tekfdi!videovax!rona
From: rona@videovax.Tek.COM (Ronald K. Anderson)
Newsgroups: sci.electronics
Subject: Re: Ideas for 2.048MHz osc.?
Message-ID: <4982@videovax.Tek.COM>
Date: 29 Apr 88 00:50:30 GMT
References: <550@hub.ucsb.edu> <4979@videovax.Tek.COM>
Reply-To: rona@videovax.Tek.COM (Ronald K. Anderson)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 58
Keywords: PLL, frequency synthesizer, Rube, 2.048MHz
Summary: Long live Rube Goldberg!

In article <4979@videovax.Tek.COM> bill@videovax.Tek.COM (William K. McFadden) writes:
>In article <550@hub.ucsb.edu> grosen@amadeus.ucsb.edu (Mark D. Grosen) writes:
>>Osciallator Question:
>>
>>I need to generate a 2.048MHz clock.  Anybody have a good idea on how to
>>do this?  Are there any power of 2 oscillators out there?
>
>If you get desperate, you could do what I do and synthesize it from a crystal
>of a different frequency.  

Or you could build your own PLL using: 

  +------+   +------+   +-----------+  +----+  +-----+
  | 1.000|   |divide|   |Phase      |  |    |  |6.144|
  | MHz  |-->|  by  |-->|Detector   |->|F(s)|->| MHz |-+   
  | OSC  |   |  125 |   |(1496)     |  |    |  |VCXO | |
  +------+   +------+   +-----------+  +----+  +-----+ |
                           ^                           |
                           |       +------+    +----+  |
                           |       |divide|    |div |  |
                           +-------|  by  |<-+-|by  |<-+
                                   | 256  |  | |3   |
                                   +------+  | +----+
                                             |
                                             +-> 2.048MHz out

  1MHz and 6.144MHz crystals are available through DIGIKEY (1-800-344-4539)
and probably many other sources.
  Motorola has a nice ap note on using their 10116 in a VCXO circuit: See
page 228 of their MECL System design handbook.
  Design your filter to reject the sum and pass the difference frequencies.
  CYPRESS makes a registered PROM that makes a great Sequential Finite
state machine. You can program them to divide by any integer under the sun,
greater than 0 and less than 257: CY7C225. Just feed back the outputs to
the respective inputs, and take your output from the SFSM msb.
  An 8 bit counter will divide by 256 nicely with no messing around with
programming. Try a 4040 12-bit counter and tap off pin 13.
  A 4018 can be simply made into a divide by 3 counter by connecting the
appropriate pins together.

  It should take no more than six IC's to implement this frequency
synthesizer.

Of course, if you have enough volume, you can get almost any of the crystal
makers to customize your own, and if you don't care about stability, make
an oscillator out of R's, L's, C's and Q's and design in some tunability!

                    
                            ;*) 

Disclaimer: I have no brother(s)-in-law(s) at any of the companies mentioned.


R.K.Anderson-Gibson-Kappel-Heist-Wood-Galbreath-Olson-Heinz
Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077 (503)627-2375
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