On 10/18/2012 11:21 AM, Tom Del Rosso wrote:
Phil Hobbs wrote:
On 10/15/2012 07:59 PM, Jim Thompson wrote:
Finally zeroing in on modeling the 74HC4046 after finding a
unpublished AppNote that gave more details on the innards. This is
what a fixed frequency looks like, simulation-wise...
http://www.analog-innovations.com/SE..._VCO_2_SIM.pdf
Comments? Scalings? (This is based on AppNote and Datasheets
claiming trip at VDD/2).
First release will be VCO only and will be in LTspice format. Once
you approve that, the PFD is virtually all logic.
...Jim Thompson
Different manufacturers give you a wide variety of ridiculously
nonlinear tuning curves for the VCO--the tuning sensitivity varies
like 3:1, and the oscillator quits below about 0.7-1.1V (@VDD=5)
depending on the device.
Which did you pick? 
(The metal gate 4046-style oscillators all stink on ice--HC4046,
HC7046, HC9046, all makers, all horrible. PD2 is nice if you stay
out of the dead zone.)
I always wondered what the "phase pulses" were good for. If you don't need
them, my 8-gate wonder* would do, and I don't think it has a dead zone.
*
SET -----+------------------------|
| |NAND--+
+-------| +--| |
|NAND--+-----+ |
+--| | |
| | |
+----------|--+ |
| | |
+----------+ | |
| | |
+--| | |
|NAND-----+ |
+-------| +--| Q
| |NAND--+-------
+--------------------------------+--| |
| |
+----------|--+
| |
+----------+ |
| | _
+--------------------------------+--| | Q
| |NAND-----+----
+-------| +--|
|NAND--+ |
+--| | |
| | |
+----------|--+ |
| | |
+----------+ | |
| | |
+--| | |
|NAND-----+--+ |
+-------| +--| |
| |NAND--+
RESET -----+------------------------|
The phase pulse output is for lock detection. PD2's output is valid in
any condition, and when using PD2, PD1 will have a 50% duty cycle when
the loop is locked and also when one of the input signals is missing.
I normally just put a window comparator on the PD2 output and use that,
since the filtered output pulls to the rail when it's out of lock.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net