benta
Electrical
- Feb 15, 2005
- 504
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.
