[sdiy] Phase-locked loops and the root of my headache

[Scott Gravenhorst]

I did a 4046 project for a FatMan.  Details here:

http://home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/4046pll.html

"Jon Darby" <jdarby at lplizard.com> wrote:
>Howdy, everyone!
>    I would really appreciate it if someone could give me (us?) an overview
>of PLLs and their audio applications, particularly the 4046A PLL with VCO
>chip. At $1.02 a pop I had to pick one up to play with it, but do not
>understand exactly what a phase locked loop is. Reading the data sheet on
>the 74HCT4046, it appears the the three different comparators are not
>inteded to be used simultaneously?  

Not usually, but who knows what wierdness can be invented.
I don't know about the 74HCT4046, but the CD4046 (or 4046)
has only 2 phase comparators.  Phase comp I will happily 
lock to strong harmonics or the fundamental.  Phase comp
II will lock only on the fundamental as long as it is within
the lock range.  Both can be musically useful.

>Does the frequency or whatever is fed
>into teh comparator input control the frequency of oscillation of the VCO?

If wired correctly, yes.

>If so, would an external master oscillator drive the PLL's range that it
>allows the VCO to oscillate within? 

mmmm, I think the answer is yes.  As long as the input signal's
frequency is within the limits of the lock range, the PLL's VCO
will follow it around like a puppy dog.

>Uggh, I'm talking out of my rear at this
>point. If anyone has a pointer or two where to start to understand PLLs or
>little projects I could do with this beast for fun fun audio fun it would
>really be swell.

You can learn a good deal from the data sheet.  There's a good 
description of what is going on, as well as formulas for calculating 
the lock range limits resistors (and cap) and the parameters for 2
different kinds of RC loop filters.

>Your pal,
>Jon Darby
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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