[sdiy] 4046 VCO overclocking a PIC

Richie Burnett rburnett at richieburnett.co.uk
Mon Aug 24 20:46:40 CEST 2015


Just ground them.

Otherwise, if the phase comparator inputs are left floating, one of the phase comparators could burst into oscillation at a few MHz. And such spurious oscillations can couple into the VCO and shift its frequency slightly.

-Richie, 

Sent from my Xperia SP on O2

---- Tom Wiltshire wrote ----

>One further question whilst on this topic:
>
>What's the best thing to do with the inputs of the unused phase comparators?
>
>Ground them? Leave them open?
>
>Thanks,
>Tom
>
>
>On 24 Aug 2015, at 09:42, Paul Perry <pfperry at melbpc.org.au> wrote:
>
>> On the subject of exotic uses of the 4046, it's worth noting that the
>> inter-manufacurer variability of 4046s is pretty wide.
>> Make sure you prototype with EXACTLY the brand you are going to use
>> in the final product..
>> 
>> As for clocking PICs, i hae never understood why this isn't done more often,
>> seeing how cheap the PIC is, and how difficult it can be to get the same result
>> in software (though that might be because I'm more an analog guy..)
>> 
>> paul perry Melbourne Australia 
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