[time-nuts] 100 MHz Source
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Apr 30 01:17:44 UTC 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
cycle.
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.
bye,
Said
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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