Looking for 4046 PLL experience
Looking for 4046 PLL experience
(OP)
I'm working on extracting a clock signal of around 15 kHz using the CMOS 4046 PLL's type II phase comparator.
The type II phase comparator should ideally lock the VCO to the input signal with a 0 degrees phase difference.
The 4046 datasheet always shows a first-order loop filter with one or two resistors and one capacitor
However, thinking back on my theory from 25 years back, a 0 degrees lock ("Type 2 PLL") normally needs a second-order loop filter (my thinking is also based on vague memories of the "Phase-Lock-Loop Design Fundamentals" application note from Motorola, AN535/D). I've unfortunately lost this application note and cannot find it on the web.
Am I right that a second-order loop filter is needed here?
And if yes, can the three-state output from the 4046 to the VCO be considered an integrator, providing the sacond pole for the filter?
Or is the datasheet misleading, so that I really need an active second-order loop filter?
Or is my thinking wrong, is a first-order filter actually sufficient?
Input from people who have worked with the 4046 is HIGHLY welcome.
(answers like "well, I think that maybe...") NOT that much.
Thank You in advance,
Benta.
PS: should someone have AN535/D lying around, I would appreciate a copy.
The type II phase comparator should ideally lock the VCO to the input signal with a 0 degrees phase difference.
The 4046 datasheet always shows a first-order loop filter with one or two resistors and one capacitor
However, thinking back on my theory from 25 years back, a 0 degrees lock ("Type 2 PLL") normally needs a second-order loop filter (my thinking is also based on vague memories of the "Phase-Lock-Loop Design Fundamentals" application note from Motorola, AN535/D). I've unfortunately lost this application note and cannot find it on the web.
Am I right that a second-order loop filter is needed here?
And if yes, can the three-state output from the 4046 to the VCO be considered an integrator, providing the sacond pole for the filter?
Or is the datasheet misleading, so that I really need an active second-order loop filter?
Or is my thinking wrong, is a first-order filter actually sufficient?
Input from people who have worked with the 4046 is HIGHLY welcome.
(answers like "well, I think that maybe...") NOT that much.
Thank You in advance,
Benta.
PS: should someone have AN535/D lying around, I would appreciate a copy.





RE: Looking for 4046 PLL experience
http://www.lansdale.com/Articles/an535.pdf
I'm not sure these are AN535 or AN535/D.
RE: Looking for 4046 PLL experience
I'm glad VE1BLL had that link. My copies got donated last year when we moved.
Z
RE: Looking for 4046 PLL experience
Reading through the note, my suspicion has been confirmed:
an active loop filter is indeed needed to get a Type 2 response (0 degrees phase error).
I'll design accordingly.
But I find it depressing that both data sheet and application notes (both for 4046 and 74HC4046) are so "mealy mouthed" on this point
Best Regards,
Benta.
RE: Looking for 4046 PLL experience
I ordered Floyd M. Gardner "Phaselock Techniques", since everyone refers to his work. I have now read it through and come to the following:
To get a type-2 response (2 poles at zero, corresponding to 2 integrators in the open loop transfer function) you indeed need either:
1: an active loop filter
2: a passive filter, but in a completely different configuration than shown in the 4046 datasheets and appnotes.
In short, the 4046 datasheet sucks!
I chose the active filter solution, prototype PCBs are ready next week, I'm interested to see the measured results.
Best Regards,
Benta.
PS: the Gardner book is not cheap, around 65 Euro. However, I have no problem paying that amount for over 40 years of experience and knowledge on PLLs. There are other books where I won't even pay the paper price, as it's been destroyed by the ink...
RE: Looking for 4046 PLL experience
One caveat about the software, which is that the installer does not run under 64-bit Windows 7. However, once it is installed (I used Windows XP compatibility mode), you can copy the folder somewhere else and run the application under Windows 7.
Glenn