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'[OT] PLL's'
2000\03\17@041107 by Peter Crowcroft

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Can anyone tell me some websites with good introductions to PLLs on them?

thank you,

regards,

Peter Crowcroft
                   DIY Electronics (HK) Ltd
               PO Box 88458, Sham Shui Po, Hong Kong
Voice: 852-2720 0255   Fax: 852-2725 0610    Email: spam_OUTpeterTakeThisOuTspamkitsrus.com
                      Web: http://kitsrus.com
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2000\03\17@045059 by Milan v.d. Swaluw

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If you know how to use i2c, you can take a look at a TSA-5055 or TSA5511
datasheet. Both the devices are PLLs and controled with i2c.

Milan.

On Fri, 17 Mar 2000, Peter Crowcroft wrote:

{Quote hidden}

***********************************
Milan v.d. Swaluw, pe1ryyspamKILLspamamsat.org
Phone: +31-6-29025090
***********************************

2000\03\17@045120 by Graeme Zimmer

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Hi Pete,

> Can anyone tell me some websites with good introductions to PLLs on them?

Actually my first stop would be the ARRL or RSGB handbooks....

Some manufactures data sheets would be next..
Start with the Exar XR2211, CD4046

and especially search Phillips and Motorola Web pages for PLL Aplication
notes.

And of course ask questions in this list...!

....................... Zim

2000\03\17@053142 by Graeme Zimmer

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> Can anyone tell me some websites with good introductions to PLLs on them?

And for a purely hypothetical practical example, let's say that you wanted
to design a FM Broadcast transmitter kit which covered from 88 to 108
MHz.......... :-)

You first design a nice stable Voltage Controlled Oscillator which covers
the required band and is tuned via DC onto a vari-cap diode.

You decide on 100 kHz channel spacing, so you arrange to divide a convenient
crystal down to generate a 100Khz reference (say divide a 4Mhz Xtal by 40).

Next the VCO is divided down to 100Khz through a Programmable Divider chip
(to Transmit on 88 MHz you divide by 880 and on up to 1080 to get 108 MHz).

The two signals are then compared in a phase/frequency comparator, which
generates an error voltage which steers the VCO onto exactly the right
frequency (and phase).

The only tricky bit is getting the time constants of the control loop
correct. The maths of this can get nasty. It is basically a PID, with just
the right amount of leading and lagging phase to overcome the mechanical and
thermal instabilities in the VCO.
Most people cheat and tweak the values empirically.

Oh yes, and to Frequency Modulate this beast you could feed a little audio
into the control line to waggle the VCO frequency.

These days all the divider chains and comparator etc are available in a
single tiny SM chip which you control over serial lines via a PIC. The PIC
Xtal probably also generates the original 4 Mhz reference. The PIC picks up
the channel number from a dip switch or rotary encoder, etc.

See I just knew that we would get back on topic eventually!!!!!


.................................... Zim

2000\03\17@063919 by Russell McMahon
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>From: Peter Crowcroft <.....peterKILLspamspam.....KITSRUS.COM>
>Can anyone tell me some websites with good introductions to PLLs on them?


Peter,

1.    Philips have a PLL design program for the 74HC/HCT297
Their order number 9398 650 00011
This was May 1989 so they may well have newer stuff too.

2.    Philips EC&A Vol 9 No 2 (1989?) pp 66 to 89 "All digital phase-locked
loops using the 74HC297"

3.    **** Exar have an old but good treatment of PLLs (not too complex but
not totally simplistic either and probably all most people need)

"Phase-Locked Loop Data Book" Exar, 1982, 80 A4 paages. Includes datra
sheets, design guides, ...
Good

Also "XR-212As modem design guide"
Exar, 1986
70 odd A5ish pages.
Not nearly as useful for general purpose design as the above book.

4.    Electronics and Wireless World August 1997 pp642-646 "Understanding
phase noise" - which you will want to do if you want to get complex with
PLLs.


I imagine there is a host of stuff on the web on PLL design. Maybe not.
I'd try a good topic concentrating serach engine like eg http://www.google.com and
just use eg
   PLL design
as search terms






     Russell McMahon
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Help the hungry at no cost to yourself!
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(* - or woman, child or internet enabled intelligent entity :-))

2000\03\17@082514 by Scott Dattalo

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On Fri, 17 Mar 2000, Peter Crowcroft wrote:

> Can anyone tell me some websites with good introductions to PLLs on them?

Peter,

Do you have a specific application in mind or are you just wanting to learn
about PLL's? If you have a specific application, then I'm sure we can give you
specific answers and suggestions. Instead of websites, you may wish to check out
a book - there are several books devoted to the subject (Floyd, as I recall, has
written one that's widely respected).

But here's a quick tutorial (that overlooks many of the essential details...)

A PLL is fed a signal of unkown but banded frequency. The PLL measures the
frequency indirectly by generating a separate waveform at the same
frequency. The algorithm for generating this separate frequency is simple:

If the incoming frequency is higher than the one synthesized by the pll, then
increase the frequency of the synthesized waveform other wise decrease it.

The difficult part of course is implementing this. How do you 'synthesize a
waveform'? How do you increase or decrease its frequency? How do you compare two
signals for differences in frequency?

These three questions are often answered in the classical PLL block diagram:

IN   +---------------+    |-------------+    +-----+       OUT
---> | phase compare | -> | Loop filter | -> | VCO | ----+-->
    |               |    |-------------+    +-----+     |
 +->|               |                                   |
 |  +---------------+                                   |
 |                                                      |
 |                                                      |
 +------------------------------------------------------+

The frequency comparsion is performed in the first block. As its name suggests,
the phase between the two signals is compared. This implies that the two signals
are the same frequency. It just doesn't make sense to speak of the phase
difference between two signals of differeing frequency. So why have a phase
comparator? Well what you can do is compare phase on a per cycle basis between
the two wave forms. For example, if the incoming signal is a sinewave that makes
a zero crossing at t = t1 then the next zero crossing of the output wave form
may be expressed in terms of a percentage of the period of the incoming wave
form. The goal of the PLL is to get those zero crossings to align.

Skipping the Loop Filter for the moment, the VCO or Voltage Controlled
Oscillator, produces a waveform whose frequency is directly proportional to a
voltage. You double the voltage and the VCO will double its frequency. The
response of the VCO, or the at which it responds to voltage changes, is a strong
function of the requirements of your system. But typically, the control to the
VCO is dithered around a DC voltage. This DC voltage is the one that causes the
VCO to produce the frequency that matches the incoming signal. But why
dither? Well, it's similar to the way an opamp works. An opamp has a positive
and negative input. If the positive input is greater than the negative, then the
opamp's output is driven high otherwise it's driven low. Without any feedback,
the output would be driven towards one of the supply rails. With feedback, the
output is driven to the voltage that minimizes (or attempts to minimize) the
difference in voltages between the positive and negative inputs. The exact same
thing (conceptually) happens here. The difference is that instead of voltages,
frequencies (or more accurately, phases) are being compared. However, this
frequency difference is translated into a (DC) voltage. But from a time point of
view, frequency is changing and DC is constant - something's got to give.

Here's where the loop filter comes in. So far I've tried to be vary abstract and
not say that the signals are sine waves or square waves or whatever. But it's
convenient to imagine the phase comparator producing pulses (they don't all do
this...). If the phase comparator's output is +1 then this may indicate that the
incoming frequency is higher than the VCO's and consequently the DC control
voltage to the VCO needs to be increased. If the phase comparator output is a 0
then the opposite case is true and the VCO needs to be decreased. But 0's and
1's need to be converted into a suitable DC control voltage for the VCO. Yhat's
the job of the loop filter. In this example, you could say, "oh, that's easy -
all you need is a low pass filter!" But in reality it depends on your VCO and on
how you design the loop filter. The problem is that you have mixed constraints.
You want the PLL to accurately lock onto a signal and you want the PLL also to
respond to changes in the incoming frequency. The accuracy constraint means
you'd like the changes in the VCO control voltage only slightly affect the VCO
frequency. On the other hand, the response to a change in frequency constraint
means you'd like the VCO to be sensitive to changes in the control voltage. This
mixed constraint problem is what typically makes PLL's a challenge.


Again, I've overlooked many of the details. In fact some of what I said may be
totally inappropriate for the PLL you need. But the concepts are generally
correct. In fact, these concepts may be applied to digital phase locked loops as
well. It all depends on what you're trying to do. So, Peter, what are you trying
to do?

Scott

2000\03\17@094638 by andy howard

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> And for a purely hypothetical practical example, let's say that you
wanted
> to design a FM Broadcast transmitter kit which covered from 88 to 108
> MHz.......... :-)


> The two signals are then compared in a phase/frequency comparator,
which
> generates an error voltage which steers the VCO onto exactly the right
> frequency (and phase).
>
> The only tricky bit is getting the time constants of the control loop
> correct. The maths of this can get nasty. It is basically a PID, with
just
> the right amount of leading and lagging phase to overcome the
mechanical and
> thermal instabilities in the VCO.
> Most people cheat and tweak the values empirically.

There are a few other considerations if you want to use this for
broadcast audio. Essentially you have a conflict between loop settling
time and audio quality. Too short a time and the thing risks unlocking
on bass audio signals.  Many professional transmitters (and even a few
of the "unofficial ones") use a dual time constant which runs fast when
the VCO is a long way off frequency but switches to a very slow rate
when it is close.
Think 4066...




Cheers,

Andy.

2000\03\17@114933 by jamesnewton

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from
http://techref.massmind.org

http://www.microlet.com/yam/. Schematics for their early FPGA, which
includes     a Digital PLL implementation.

All digital PLL is generally not a good choice to reduce jitter (unless your
jitter's real bad to begin with). Jitter attenuators do the job, though
http://www.dalsemi.com/DocControl/PDFs/2188.pdf...

The Bell Labs tech journals from the mid 1970's have tons of articles on
jitter in communication systems.

The bible on analog PLLs theory is "Phaselock Techniques by Gardner (1979)"

"Phase Locked Loops : Design, Simulation, and Applications" by Best has a
very basic intro to DPLLs

"Monolithic Phase-Locked Loops and Clock Recovery Circuits : Theory and
Design" from the IEEE is more current, and has a good PLL theory section.

http://www.infosite.com/%7Ejkeyzer/piclist/2000/Feb/1777.html     Using a
PLL and an integrator to measure the amplitude of a signal at a given
frequency an reject noise (a one channel spectrum analyzer)

---
James Newton EraseMEjamesnewtonspam_OUTspamTakeThisOuTgeocities.com 1-619-652-0593
http://techref.massmind.org NEW! FINALLY A REAL NAME!
Members can add private/public comments/pages ($0 TANSTAAFL web hosting)


{Original Message removed}

2000\03\17@183451 by Graeme Zimmer

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> There are a few other considerations if you want to use this for
> broadcast audio. Essentially you have a conflict between loop settling
> time and audio quality.

Yes, of course.....but I was giving the abridged version!

The usual trick is to modulate both the Control Voltage (for higher freq
audio) and also the Reference Oscillator (for lower freqs).

BTW, you CAN just modulate the loop, if you are using a Frequency
Comparator, and you just let the phase lock be broken by the bass
frequencies....

In otherwords it becomes a Frequency Locked Loop, rather than a PLL..

............................ Zim

2000\03\17@184934 by Graeme Zimmer

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> All digital PLL is generally not a good choice to reduce jitter (unless
your
> jitter's real bad to begin with). Jitter attenuators do the job, though
> http://www.dalsemi.com/DocControl/PDFs/2188.pdf...

And for something even further ...OT...

The rumor has it that Jittered clocks are absolute murder on the new Digital
TV signals...

Supposedly the authorities are busily re-writing the EMC specs to close the
jittered-clock loophole?

should be interesting.....

..................... Zim

2000\03\19@222736 by David Lions

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How do you actually make a transmitter TRANSMIT?!?  I have made many kits
in my time, but never understood this.

Suppose there is an oscillator running at say 100MHz, which you modulate
with your input signal...

Now how you convince the high frequency signals in your circuit to just
shoot off into free air?  I mean, HOW DO YOU TRANSMIT?!?

At 09:27 PM 3/17/00 +1100, you wrote:
{Quote hidden}

2000\03\19@234316 by Graeme Zimmer

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> Now how you convince the high frequency signals in your circuit to just
> shoot off into free air?  I mean, HOW DO YOU TRANSMIT?!?

Feed the RF to an Antenna !

This ref might help explain..

   http://www.ednmag.com/ednmag/reg/2000/03022000/05ms624.htm

.................. Zim

2000\03\20@105614 by Don Hyde

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???  That's what the antenna's for!

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2000\03\20@155354 by l.allen

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>
> Now how you convince the high frequency signals in your circuit to just
> shoot off into free air?  I mean, HOW DO YOU TRANSMIT?!?
>

Thats a good question...
Radio is my brackground... qualifications and all that...
and its a bit of a mystery to me to. What you are doing
with a transmitter is taking electricity from your power
source and putting it into the air/ space whatever.
The device we use for this is an aerial which is an
efficient interface between the air and the circuit.
Maximum power transfer from the aerial to the air will
occur when the aerial is matched to the impedence of the
transmitter (with losses).
Radio waves are both electric and magnetic so if you use
an open ended wire you are utilising the electric
component to match with, if you use a loop you are
matching with the magnetic component.
So there are certain lenghts of aerials that we can use
dependent on the frequency we are transmitting and how
efficient we want our aerial to be. ..... its a big topic that
is covered by a huge array of books but a good start is to
connect a 1/4 or 3/4 wavelenght aerial to your output.
Wavelenght(metres) = speed of light(300,000Metres/Sec)
/ frequency.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

2000\03\20@165341 by James Paul

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some other little tidbits to add to this discussion....
The match between the aerial and the surrounding space is also
important to the effeciency of the aerial.  The effeciency of
a given antenna (aerial) can be improved to a point by making
the elements as large as practical given the constraints of the
frequency and the bandwidth allowable.   Also, the height above
the terrain is an important factor.  Generall speaking, the
higher, the better.  But, there is a practical limit.  And, the
material the antenna is made of is somewhat important to
effeciency.  And, I agree with what Lance said below.  There
are many many volumes of information and antenna theory out
there.  The web is a good place to look.  Especially at HAM
Radio sites.  You'll find a wealth of information here.

                                         Good Luck,


                                            Jim


On Mon, 20 March 2000, Lance Allen wrote:

{Quote hidden}

KILLspamjimKILLspamspamjpes.com

2000\03\20@170225 by l.allen

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You wrote..

>  some other little tidbits to add to this discussion....
>  The match between the aerial and the surrounding space is also
>  important to the effeciency of the aerial.  The effeciency of
>  a given antenna (aerial) can be improved to a point by making
>  the elements as large as practical given the constraints of the
>  frequency and the bandwidth allowable.   Also, the height above
>  the terrain is an important factor.  Generall speaking, the
>  higher, the better.  But, there is a practical limit.  And, the
>  material the antenna is made of is somewhat important to
>  effeciency.  And, I agree with what Lance said below.  There
>  are many many volumes of information and antenna theory out
>  there.  The web is a good place to look.  Especially at HAM
>  Radio sites.  You'll find a wealth of information here.
>
>                                           Good Luck,
>
>
>                                              Jim
>
It is such an involved topic that I didnt know how much to
cover as an ' intro '. I tried to stick to the basic concepts.
Being a UHF specialist I have to conclude radio is
bordering on a bit of a black art, I love it when a transistor
in the front end is short/dead/missing in a 800MHz RX
and it just lowers the s/n ratio a bit but essentially the RX
keeps working.

_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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