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

[Jon Darby]

Thanks, Magnus, I appreciate the primer. What is a typical application of
the phase-locked loop? I can kind of pick up smatterings of filter
applications, but don't understand what role it plays. I'll look for the
book tonight. The 4046 seems really interesting from the datasheet and I
feel like I'm beginning to take that first dive into Lake Understanding The
Application of Electronic Components.

Thanks again,
Jon Darby

----- Original Message -----
From: "Magnus Danielson" <cfmd at swipnet.se>
To: <jdarby at lplizard.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, August 31, 2001 6:52 PM
Subject: Re: [sdiy] Phase-locked loops and the root of my headache


> From: "Jon Darby" <jdarby at lplizard.com>
> Subject: [sdiy] Phase-locked loops and the root of my headache
> Date: Fri, 31 Aug 2001 17:41:50 -0400
>
> > Howdy, everyone!
>
> Howdy Jon,
>
> >     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.
>
> The 4046 (and its derivates) are absolute classics in the PLL world.
>
> Let me tell you, I have several books on the topic itself, so it is
> not something one summarizes with deep insight, but an initial tour of
> what can be acheived is not a problem.
>
> > Reading the data sheet on the 74HCT4046, it appears the the three
> > different comparators are not inteded to be used simultaneously?
>
> This is correct. They share common inputs, but you use the output of
> your choice to best match your application. At rare cases one uses one
> of the outputs for lock detection, so then you effectively use two
outputs.
>
> > Does the frequency or whatever is fed into teh comparator input
> > control the frequency of oscillation of the VCO?
>
> Yes, but not only the frequency, you will also lock the VCO output
> phase in relation to the input signals phase. However, this phase
> relationship may be many different things than 0 degrees.
>
> Also note, you must set up the VCO for the propper frequency
> range. While it may be very wide, the center frequency of the
> oscillator is of interest since it is actually from this you modulate
> the VCO up or down.
>
> > If so, would an external master oscillator drive the PLL's range that it
> > allows the VCO to oscillate within?
>
> Yes, you can make the VCO track the frequency of some reference (or
> master) oscillator/signal.
>
> > 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.
>
> There is one book called "Phase Locked Loop" by Best which could be a
> good starter book. It has a very practical side to it and talk about
> actual components. Examples with 4046 is there for instance. It comes
> with a program which allows you to simulate the behaviour of a PLL, so
> you can get a feel if you are in the right neighborhood before
> actually building.
>
> I do not know of a good web-site thought. The datasheets is about it
> as I know it from the top of my head. Philips 74HC4046, 74HC7046 and
> 74HC9046 datasheets contain quite alot of design help for a
> datasheet. They basically tossed in appnotes into it.
>
> One of the things which one should know is that you are not required
> to use the VCO sitting in the 4046, you can use another VCO. The expo
> input is however an issue which most probably causes some upset to the
> system.
>
> Cheers,
> Magnus