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Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
'morning all, every time I see a DIP 4046, it's always got a ceiling of 1.4 - 2.4 MHz...
I'm wondering about working with a higher centre frequency between 5MHz and 20MHz... an idea I've had includes: put a schmitt triggered buffer/inverter on the aerial input, followed by a divide-by-four chip, then into the "signal" pin of the PLL...
similarly you put a 'multiply by four' chip on the mode1 comparator output, and feed the 4x signal into the gate-drivers... giving you four times the available 'range' of the centre frequency... but this seems clumsy, and even then I don't see any "multiply by four" quick and easy CMOS chips, hehehe
better ideas?
rumour has it there's a surface mount 18MHz-capable cd4046 out there somewhere... or is this an old wives tale?
cheers =)
[edit: oops, I'm stupid. I just saw a link on a page to an 74HC4046... umm duhhh :P... ideas still welcome :D]
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I think the usual thing to do is put a divider on the input to the PLL chip, and then use the voltage output of the PLL to control a voltage controlled oscillator - containing a varicap diode.
You can use standard zener diodes (about 20v ones) as the varicap - once you bias them with a voltage, the capacitance changes, altering the frequency of the oscillator.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
AFAIK there is no such thing as a quick and easy multiply by four chip. Why not just use the 74HC4046? It's identical to the old 4046 except it's faster and the supply voltage is restricted to 4.5 - 5.5V.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Steve Conner wrote ...
AFAIK there is no such thing as a quick and easy multiply by four chip. Why not just use the 74HC4046? It's identical to the old 4046 except it's faster and the supply voltage is restricted to 4.5 - 5.5V.
Yah, I just saw that... the motorola ones go up to 18MHz, too =)
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higher frequency phase-locked-loop
