Finally zeroing in on modeling the 74HC4046 after finding a unpublished AppNote that gave more details on the innards.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...
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
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Funny. I put a HC7046 into a design recently. Unfortunately there are no design tools for calculating the loop filter components. So how about modeling the HC7046? It is much more interesting because of the lock detect output which can be used as a reset.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
I investigated all the HC versions (HC4046 from several vendors, HC7046, HC9046) about a year back, iirc, and their oscillators are all junk compared with the ancient metal-gate 4046. They're horribly nonlinear, all in different ways, which makes it really hard to build a good PLL. What's worse, their oscillators quit when their control voltages are within a volt or so of ground (the actual threshold for misbehaviour varies from device to device).
The 7046 is enough more expensive that I'd be much happier spending the dough on a better oscillator, and using the back end of a normal HC4046 from a good vendor.
Cheers
Phil Hobs
-- 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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Funny. I have a HC7046 schematic right here in front of me.
Personally I think lock detectors are a farce. But I can certainly add it in.
As for "design tools for calculating the loop filter components", come on Nico, that's math, you don't need a "tool" :-)
See...
for a primer. Adjust analysis for edge-detecting PFD "gain". ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Phil, What sort of non-linearity are you seeing? All I can think of is perhaps using non-cascoded current mirrors, or just using a gross un-boosted follower. Is it just a bow in the control curve, or are you seeing bow in the capacitor charging voltage? ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
It occurs to me that the variable current input quits at about 1*VTH. So you were trying to get to zero frequency ?:-)
Add some offset current and it won't quit oscillating. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Further recollections... I've used OpAmps to force the control linearity. Been a long time, maybe 30 years since I had a VCM need.
You could, of course, resurrect one of my MC4024's from the mid '60's :-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
...Jim Thompson | mens | | et | | |
test reply,
(Google won't let me post??)
George
...Jim Thompson | mens | | et | | |
Hi Jim, Phil. Here?s a plot for a 74HC4046
And for different ?charging? resistors.
The lines were just drawn by eye.
As Phil says the oscillations stop if the control voltage falls below ~1Volt. (I never used the metal can version so don?t know what I?m missing.)
George H.
(trying onece more then)
[snip]
Thanks for the plots. Quite puzzling, I'd expect drooping at the high end of the F vs V plot due to gate delays.
I think Phil didn't use an "offset" resistor
Both attempts posted :-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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.)
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
The metal gate version works over about 1000:1 range, and is very respectably linear--a few percent IIRC, which is much better than good enough for inside a PLL. It's really quite pretty in a small way.
The HC parts' nonlinearity is all over the map depending on the vendor, and that messes up the loop dynamics really badly. Spicing the HC4046 oscillator will definitely be "a trap for young players", as Dave Jones says.
With the loop gain varying 3:1 with control voltage, and the centre frequency being a very poorly controlled function of the RC, you have to make HC4046 loops ridiculously overdamped in the normal case to avoid loop instability. If you're using lead-lag compensation, you have to put the zero a factor of at least 5 below the nominal unity gain cross, whereas with a well-behaved VCO, you can put it right at the unity gain cross and have 45 degrees' phase margin.
I'd far rather use an OTA integrator/Schmitt trigger oscillator or something like that, with the 4046 PDII.
The HC4046 has its uses, but not nearly as many as if it were really a faster CD4046.
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
Phil said metal _gate_ version, i.e. a plain ol' 4046.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Oh, I should know -- OTA Integrator?
I wish someone would take the 3-state phase detector from the 4046 and put it into a 6-pin SOT and call it TinyLogic or whatever. It would save ever so much board space.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
I don't think most users fret over the incremental slope. The "follower" variation is trivial to fix by adding an OpAmp. Sinking one end of the capacitor into the substrate diode every half cycle is something you have to live with if you like 4046's. I'm doing this for fun (and requests from this group)... I wouldn't use one myself. Get my MC4024 if you want better linearity. I think there's also a PECL copy, but I don't remember the part number off the top of my head. Or use a V-to-F chip.
That's noted on the data sheet. Why does that give you such heartburn? Do you really need zero frequency?
I have the most complete data on the TI 'HC4046, but I was aiming sort of average ;-) since I'm building it from behavioral blocks.
I would guess that you're one of the few people in the world that would need a flat-ass accurate fit to one particular version.
What do you really need? An accurate V-to-F? ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
W/O the charge pump, it's just a dual-D plus a quad 2-in-NAND. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
)
Ahh thanks Tim, the CD4046? I guess I should order some.
OTA = transconductance amplifier? (not sure what O is.)
George H.
That's a lot more board space than a SOT-23.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
If you can round up some customers who would pay for it, I'll design and fab it.
Unfortunately today's average customer wants the whole world on that one chip, NOT just a building block. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Operational transconductance amplifier, e.g. an LM13700--basically a bunch of current mirrors, controlled by a diff pair so that you can set the tail current of the pair and the output is a current source equal to delta I_C, which pulls almost to the rails. You hang a cap on the output, buffer it with the built-in Darlington, and feed that into a Schmitt trigger, which can be made from the other half of the LM13700 in a pinch. The Schmitt switches the diff pair of the integrator stage, so you get a reasonably decent triangle wave with a slope proportional to the current you program the OTA integrator with. Works well at low speed, over a wide range, and the component count is lowish.
Agreed. But it would cost a bunch more, because the 4046 is the jellybean.
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
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