[time-nuts] 100 MHz Source

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Apr 29 21:17:44 EDT 2008

Hi Dick,
I think a very inexpensive and simple way to multiply the 10MHz to 100MHz  is 
the following. It only uses three standard CMOS chips:
Use a 100MHz VCXO to generate your output frequency. Digikey has one for  
$28: Digikey number 744-1213-ND. This part has about -160dBc/Hz noise floor,  
quite nice.
For the simple control logic:
Use an NXP 74LVC163 counter with preload to divide 100MHz by 5 to get  20MHz. 
Use a 74LVC74 to get a 10MHz reference out of this 20MHz, with 50% duty  
Feed this 10MHz, and your 10MHz reference signal into an Exor gate  
(74LVC86). This is the phase comparator.
Low-Pass filter the output of the Exor gate with a low pass filter that has  
<1Hz bandwidth. Say 2.2K Ohms into 100uF Tantalum with 100nF cap in paralell,  
into another 2.2K Ohms/100uF Tantalum low pass filter. This signal drives the 
 VCXO input.
That's all folks.
Should cost you less than $35 including shipping, and generate a very  stable 
100MHz signal. Jitter, very low Phase Noise, etc determined by the 100MHz  
VCXO. ADEV determined almost entirely by the 10MHz reference source.
In a message dated 4/29/2008 14:17:50 Pacific Daylight Time,  
mctylr at gmail.com writes:

Run a  100 MHz oscillator in a  divide by 10  PLL (Phase Locked  Loop)
configuration, compared to your 10 MHz standard? If the Motorola  /
Freescale MC145170 (-2) was still in production, that might be a  good
one to use. Maybe National  LMK03002.

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