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

[John L Marshall]

If you put dividers after both oscillators you can create interesting
frequency ratios. The divide by after the master oscillator causes the PLL
to track at a fractional frequency. The divide by after the locked
oscillator causes the PLL to track at multiple frequency.  If you use two or
more PLL you can create chords such as 4:5:6:7 major seventh.


----- Original Message -----
From: Jon Darby <jdarby at lplizard.com>
To: Magnus Danielson <cfmd at swipnet.se>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, August 31, 2001 3:47 PM
Subject: Re: [sdiy] Phase-locked loops and the root of my headache


> 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
>
>