[sci.electronics] cheap hi-speed oscillator

hamilton@udel.edu (andrew hamilton) (11/07/90)

Anyone know how to make a cheap variable frequency oscillator that will
oscillate in the MHz range.  555's don't seem to be able to do more than
about 500KHz.

Thanks in advance,

Andrew.

ftpam1@acad3.fai.alaska.edu (MUNTS PHILLIP A) (11/07/90)

In article <35596@nigel.ee.udel.edu>, hamilton@udel.edu (andrew hamilton) writes...
> 
>Anyone know how to make a cheap variable frequency oscillator that will
>oscillate in the MHz range.  555's don't seem to be able to do more than
>about 500KHz.
> 
>Thanks in advance,
> 
>Andrew.

     Here is one of my favorites.  It should work from less than 1 Hz to several
MHz, depending on the chip used and the resistor and capacitor.  The order of
magnitude of the frequency will be 1/RC.  Stability and spectral purity is not
very good, but it makes a decent digital system clock.

                                     R
                             _____/\/\/\_____
                            |                |
                            |     |\         |
                            |     | \        |
                            |     |  \       |
                            |     |   \      |
                            |     |    \     |
                            |-----|     O---------> Output
                            |     |    /
                            |     |   /
                          __|__   |  /  74C14, 74HC14, etc.
                       C  _____   | /
                            |     |/    Not 74C04, 74HC04, etc.
                          __|__
                          / / /         A TTL 7414 can also be used but
                                        component values are more critical.

misra@matt.ksu.ksu.edu (11/07/90)

In article <35596@nigel.ee.udel.edu> hamilton@udel.edu (andrew hamilton) writes:
>
>Anyone know how to make a cheap variable frequency oscillator that will
>oscillate in the MHz range.  555's don't seem to be able to do more than
>about 500KHz.
>
>Thanks in advance,
>
>Andrew.

	Are you sure about that? I have seen sch using the 555
and i think if you change the caps you get it going in the MHZ range.


*************************************************************************
*                                *                                      *
*   - I will put in something    *       Brijesh Misra                  *
*     soon                       *                                      *
**********************************       misra@ksuvm.ksu.edu            *
*       FOR RENT                 *       misra@matt.ksu.ksu.edu         *
*                                *                                      *
************************************************************************* 

mark@mips.COM (Mark G. Johnson) (11/07/90)

In <35596@nigel.ee.udel.edu> hamilton@udel.edu (andrew hamilton) writes:
   >
   >Anyone know how to make a cheap variable frequency oscillator that will
   >oscillate in the MHz range.  555's don't seem to be able to do more than
   >about 500KHz.
   >

For $0.35 Digi-Key will sell you a 74HC14.  How about hooking it up as
an ultra cheapo RC relaxation oscillator:

     +------------------------------------------------+
     |                                                |
     |     50K potentiometer                 +        |   +
     |                                       | \      |   | \
     +-----/\/\/\/\/\---+---------+----------|  >0----+---|  >0---- OUTPUT
                A       |         |          | /          | /
                |       |         |          +            +
                +-------+       -----
                                -----
                                  |   68pF
                                  |   capacitor
                                 GND

This ckt will top out around 12 MHz  (for faster still, reduce the cap
value and be more careful with layout).  Beware, the 74HC family works
from 2 to 6 volt supplies; unlike the old RCA family, these fellers
poop out and die at VCC=6.5V.
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}

henry@zoo.toronto.edu (Henry Spencer) (11/08/90)

In article <1990Nov6.222448.15507@maverick.ksu.ksu.edu> misra@matt.ksu.ksu.edu writes:
>	Are you sure about that? I have seen sch using the 555
>and i think if you change the caps you get it going in the MHZ range.

Bear in mind that 555s from different manufacturers may have somewhat
different characteristics.  It's entirely possible that *his* won't
run at MHz speeds.
-- 
"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
"Not to worry."                        |  henry@zoo.toronto.edu   utzoo!henry

umapu02@cc.ic.ac.uk (D.A.G. Gillies Supvsr Dr K.J. Bignell) (11/09/90)

In article <1990Nov6.212128.16965@hayes.ims.alaska.edu> ftpam1@acad3.fai.alaska.edu writes:
>In article <35596@nigel.ee.udel.edu>, hamilton@udel.edu (andrew hamilton) writes...
>> 
>>Anyone know how to make a cheap variable frequency oscillator that will
>>oscillate in the MHz range.  555's don't seem to be able to do more than
>>about 500KHz.
>> 
>>Thanks in advance,
>> 
>>Andrew.
>
>     Here is one of my favorites.  It should work from less than 1 Hz to several
>MHz, depending on the chip used and the resistor and capacitor.  The order of
>magnitude of the frequency will be 1/RC.  Stability and spectral purity is not
>very good, but it makes a decent digital system clock.
>
>                                     R
>                             _____/\/\/\_____
>                            |                |
>                            |     |\         |
>                            |     | \        |
>                            |     |  \       |
>                            |     |   \      |
>                            |     |    \     |
>                            |-----|     O---------> Output
>                            |     |    /
>                            |     |   /
>                          __|__   |  /  74C14, 74HC14, etc.
>                       C  _____   | /
>                            |     |/    Not 74C04, 74HC04, etc.
>                          __|__
>                          / / /         A TTL 7414 can also be used but
>                                        component values are more critical.

 The problem with this circuit is that it has quite high sideband noise (that
said, I use it in almost all low stability applications I need. It is great for
multiplexing LED sticks for example).For slightly more dosh, this one works
great, and it gives TTL levels up to 25 MHz.It ain't as complex as it looks.


						   ______ +5V
						     |
						      \
						      /
                                                      \    'LS00
						      /     ___
		1/4 'HC04			     |_____|   \
	      |\       _________		     |  |  | &  |O----> output
       _______| \     |         |<----Co-ax cable  |/   |__|    |
      |       |  O-----------------/\/\/\/\--------| T1    |___/
      |       | /  |  |_________|    R3      |     |\
      |       |/   |  __|__		     |       |
      |    R1      |   ___		  ___|___    |
      |___/\/\/\___|    _		    / \    __|__
      |            |                 1N914 /   \    ___
      |            \                       -----     _
      |            / R2                      |
      |            \			     |
      |     __     /			   __|__
      |   || X||   |			    ___
      |---|| L||---|			     _
      |   || 1||   |			 
      |     --     |
    __|__        __|__
    __ __ C1     __ __ C2
      |            |
      |            |
    __|__        __|__
     ___          ___
      _            _

 R1 = 10M
 R2 = 100k
 R3 = 1k
 R4 = 1k
all metal film ( I use 0.6W,1% simply because they are the cheapest I can get)
 C1 = 20pF
 C2 = 20pf trimmer (frequency adjust)
 XL1 = crystal,100kHz to 28MHz (higher frequency may be dodgy)
 

 The co-ax cable is simply a way of moving RF around the PCB.It can probably be
omitted for certain applications.The frequency variability is not very high
(a few ppm) but can be divided with logic to give a very wide range of 
frequencies.I would recommend the 74LS292 and 74LS294 programmable frequency
dividers.The '292 divides the input frequency by 2 to the power n,where n is a
number from 2 to 31. Alternatively you could use cascaded 74167 BCD rate 
multipliers to generate a very accurately settable output in the Hz to MHz
range,but here you're talking about frequency generators,and that might be a 
little complex.It's still a very feasible option though.





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richm@amc-gw.amc.com (Rich Moran) (11/09/90)

In article <35596@nigel.ee.udel.edu> hamilton@udel.edu (andrew hamilton) writes:
}
}Anyone know how to make a cheap variable frequency oscillator that will
}oscillate in the MHz range.  555's don't seem to be able to do more than
}about 500KHz.

Try a 74S124.  It's a dual voltage-controlled oscillator.  Typical Fmax is
85MHz, according to the TI data book.

Rich

-- 
=============================================
Rich Moran
richm@amc.com
=============================================

pepke@gw.scri.fsu.edu (Eric Pepke) (11/10/90)

In article <3978@amc-gw.amc.com> richm@amc-gw.amc.com (Rich Moran) writes:
> Try a 74S124.  It's a dual voltage-controlled oscillator.  Typical Fmax 
is
> 85MHz, according to the TI data book.

That's pretty good.  Does anybody know of a VCO that will go up to 110 
MHz?  Or alternately, a good source of 110 MHz crystals and an oscillator 
circuit that will drive them?  I just need a tiny deviation from 110 MHz, 
so a little variable capacitor might be all that is needed.

Eric Pepke                                    INTERNET: pepke@gw.scri.fsu.edu
Supercomputer Computations Research Institute MFENET:   pepke@fsu
Florida State University                      SPAN:     scri::pepke
Tallahassee, FL 32306-4052                    BITNET:   pepke@fsu

Disclaimer: My employers seldom even LISTEN to my opinions.
Meta-disclaimer: Any society that needs disclaimers has too many lawyers.

grayt@spock (Tom Gray) (11/13/90)

In article <1376@sun13.scri.fsu.edu> pepke@gw.scri.fsu.edu (Eric Pepke) writes:
>
>That's pretty good.  Does anybody know of a VCO that will go up to 110 
>MHz?  Or alternately, a good source of 110 MHz crystals and an oscillator 

Check out the Motorola ECL catalogs. The ECL VCO's will operate at above
100Mhz and will be very stable and controllable with +5V.

To avoid other questions about ECL's. The VCO's will work on +5V without
any problems.
 

henry@zoo.toronto.edu (Henry Spencer) (11/14/90)

In article <3978@amc-gw.amc.com> richm@the-end.amc.com (Rich Moran) writes:
>Try a 74S124.  It's a dual voltage-controlled oscillator.  Typical Fmax is
>85MHz, according to the TI data book.

NO!  NO!  NO!  The S124 is worthless junk!  I speak from experience.

If you must use a 7400-series part, look for (I think) 74S624.  That's a
version that's been fixed to work.  I don't swear to the part number, as
my references are at home and it's been a while.

The part you want for fairly high-frequency VCOs, actually, is the MC4024.
Beware, this is not a CMOS part, it is a TTL part with an odd number; the
Motorola part number for the CMOS part that others would call "4024" is
MC14024.  You can often find the MC4024 in the "odds and ends" sections
of catalogs.
-- 
"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
"Not to worry."                        |  henry@zoo.toronto.edu   utzoo!henry

henry@zoo.toronto.edu (Henry Spencer) (11/14/90)

In article <1376@sun13.scri.fsu.edu> pepke@gw.scri.fsu.edu (Eric Pepke) writes:
>... Does anybody know of a VCO that will go up to 110 MHz?

I had cause to look into this a few years ago; at that time, the answer was
"welcome to the warm world of ECL".  Such parts do exist, but they are not
particularly easy to work with.  The MC1658 was, at the time, grand champion
of the VCO chips.
-- 
"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
"Not to worry."                        |  henry@zoo.toronto.edu   utzoo!henry

tell@oscar.cs.unc.edu (Stephen Tell) (11/14/90)

I don't know if its cheap, but the 1989 _Signetics Linear Data Manual
Volume 1: Communications_ has a chip called the NE568, called a "150 Mhz
Phase locked loop."  One component of a PLL is, of course, a VCO.
It looks like you should be able to use the VCO alone if want, although
the output would probably need some work to get to a logic signal.

Anybody know if this chip is any good?

While we're talking PLL's, does anyone have any suggestions on chips or other
approaches to using a PLL as a frequency synthesizer to generate 50 and 25 Mhz
ECL clocks that are in phase with an incomming 25Mhz ECL clock?  We'd prefer
the clocks to stay pretty close to the rated values even when the input
clock goes away, although the system really doesn't have to function that
way, so I suppose a VCXO is in order.   We need to clock in the incomming
data from the interface cable at 25Mhz and run some control logic at 50Mhz.
All the incomming signals are differential ECL, but we're planning to convert
to TTL right away, with the possible exception of the clock generation/
distribution stuff.     Thanks for any suggestions.

--------------------------------------------------------------------
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