PLL

Where can I find the simplest phase lock loop circuit?

If I can use just transistors or simple logic gates to produce it, that would be great.

 

The CMOS 4046 is probably the simplest and easiest PLL to use, building one from discrete devices is likely to be a LOT more complicated.

 

I want to learn how to build my own. The more I learn, the smarter I get.

 

You need a ref frequency, VCO, XOR gate for a phase detector, LPF for smoothing and a divide by N counter if you need the output F to be N(times) the reference frequency. This could be implemented using discrete chips.

 

If you get the datasheet for a PLL they ususally have a block repesentation of what is in one

 

Without telling my age, I was experimenting with electronics before IC's were available. To build a phase lock loop in those days was next to impossible. As it has been said before the 4046 is the easiest to build a PLL with. Add a 4017 divide by 10 counter and you got it all. The 4046 has the VCO and the phase detector in one package. Learning how the individual blocks work and then how the system works should be satisfying.

 

Actually not!, a common feature of TV's was a discrete PLL, even available as an update for many really old sets - it was called 'flywheel sync'. By using a PLL around the line oscillator stage it reduced picture 'tearing' on weak signals - by the mid 60's it was universally used in production TV's.

 

Not sure I really agree with that ... I suppose it depends on how wide a 'lock range' you want and wierd stuff like that but I have built a variant of The Poor Man's Caesium Clock, using an XOR detector and bandgap-tuned crystal oscillator, nice and simple and works OK (after some tweaking of monostables in the TV line seperator ??).

mstechca
Read that article (link) - I think it's a good into to PLL useage.

 

Rather more complicated than a 4046 though, that has everything in one DIL package (including two types of phase detector), and requires very few external components.

 

Unphased and still looping !

mstechca
I was searching for info about Thandar LA160 and stumbled across this ...
http://www.holmea.demon.co.uk/Ethernet/PLLQA.htm
I thought it might be of interest ?

Nigel OK, maybe I should concede this one - I think the discrete circuit is good for seeing how a PLL works though! (and 1 XOR, a varicap and Xtal oscillator isn't that complex :wink:

 

74HC/HCT4046 has a third phase detector
http://www.electro-tech-online.com/custompdfs/2005/01/74HC_HCT4046A_CNV_2.pdf

 

someone knows the pll and vco that can works up to 70Mhz???

 

personally i'd just get an LM565 and learn how to use it from there...


and Zener_Diode, an LM565 should be able to handle 70MHz easily...

 

In it's datasheet is written "vco maximum frequency is 500Khz.
http://www.chipcatalog.com/National/Datasheet/LM565.htm
And I need 70MHZ....

 

Generally you would use a discrete VCO for high frequencies, the rest of the PLL generally runs at far lower frequencies (with the VCO divided down).

 

ok....
And what VCO should I take?

 

There are a great many RF oscillator designs available, use anyone you like, and make it a VCO by adding a varactor diode across the tuning coil.

If this is still about the radio design you asked about previously, the suggested chip had a VCO built-in.

 

I want a VCO chip. what chip number do you know???

 

I've never looked for any, mostly discrete oscillators are used for VHF frequencies. You could try searching at Motorola, I seem to recall they used to do a lot of PLL chips for radio use.

 

Here is a PLL I cranked out that has no ICs, and only one type of transistor. You can use any general purpose NPN.
If anyone wants to sim it in SwitcherCAD III, I am including PLL_transistor.doc. Copy and paste the text into Notepad and save as PLL_transistor.asc in the SWcad main directory. Then start SwitcherCAD III and open PLL_transistor.