Reminds me of the "sorting algorithm" where to sort an unordered indexed set you start a thread for each element and put the thread to sleep for X time interval, where X is the index of each element in the set, joining the data in each thread in temporal order as they return.
Or maybe you're talking an unbounded VCO? That can cause harmonic locks, or no lock at all. ...Jim Thompson
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| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
It's the unlocked condition we're talking about, so the PD phase null is no t in view--the PD is putting out a mildly distorted sine wave.
It's the phase of the loop filter/amp transfer function (amplitude/phase vs beat frequency) that matters for pull-in and false lock.
Cheers
Phil Hobbs
Are you disobeying Bode ?:-) You're supposed to put your extra poles well-beyond where the loop gain passes thru 0dB.
Maybe I'm missing something? But I've built a LOT of PLL's that didn't have such a problem. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
The loop is unlocked, so the beat frequency is much larger than the loop bandwidth. That's why the asymptotic phase is relevant.
Sure, lots don't. It's not an issue with PFDs, of course, but XOR, multiplier, S/H, and D-flop PDs are vulnerable.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Aha! There's an equation somewhere in Gardner that says that loop bandwidth must be such-and-such to guarantee acquisition... otherwise you need "aided" acquisition.
All my analog loops have been multipliers of some sort. I don't use digital equivalents in analog situations.
I once tried that TI digital PLL abortion in a modem application, then ended up using it _only_ for transmit... that's where that S-curve discriminator for receive originated (~1980 :-)
I ran a test using that approach... out from Phoenix to Louisville (a friend's house) then back on a separate line... a really noisy connection (acoustic muff's ;-)... got an excellent BER.
** I cheated just a wee-bit with the "acoustic" muffs... inquire within for details >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
As you narrow the loop BW, the acquisition time goes as 1/f_0**2. That gets old in a hurry. But the real limit is the pull-in signal becoming smaller than the worst-case offset voltage. That's why the Schmitt in my auto-sweep circuit has to provide 2-3x the maximum offset voltage in the op amp and PD combined.
I'm a fan of the Mini Circuits MPD-1, which has a volt or so of output and pretty low offset--1 mV or less. Less offset means less AM-PM conversion.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
What offset voltage? Are you trying to cope with signals so small that an analog multiplier offset is troublesome? Loop gain, with an analog PD, is signal amplitude dependent.
I don't use off-the-shelf PD's >:-) ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
We need to distinguish clearly between the in-lock and out-of-lock behaviour. (This has been a continual difficulty in this exchange.)
When the loop is in lock, there's some nice big voltage slope on the PD output--on the order of a volt per radian--so small offsets cause only small phase errors.
Those phase errors do result in small amounts of AM-PM conversion, which you may or may not care about, depending on how much AM noise there is and how tight the phase noise spec is.
When you're out of lock, the nice big PD slope goes away, leaving a beat note and a small amount of DC from the sum of the pull-in signal and the offsets. This is true irrespective of the input amplitude.
The DC pull-in signal is very small, so you care a good deal about offsets (if it weren't, pull-in wouldn't be so slow). With the self-sweeper, unless you short it out when the lock detect is true, it imposes a DC offset at least a few times the worst-case sum of the offsets. You pick it to be that size in order to get reliable locking in a reasonable time, without trashing the AM-PM performance too badly.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Gack! Looked it up. That's just a mixer. No wonder you fret offsets.
I have built on-chip PD's up to 5GHz. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
Spice is like a sports car... Performance only as good as the person behind the wheel.
It's a very strong mixer, with high output voltage (1V/rad), very low noise, and low offset (200 uV or so). In general it's a much better choice than Gilbert cells for making rugged analogue PLLs.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
With what analog input signal level? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
Here's an analog phase detector (~1974) with coherent AGC...
to get both the loop gain constant _and_ get synchronous detection of the modulation. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
Spice is like a sports car... Performance only as good as the person behind the wheel.
Should have mentioned... this was BC (before CAD), no simulation, breadboarded, tested in a farmer's field next to Bowmar, then "chip'd" ;-) ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
Nominal is about +7 dBm LO, slightly less on the RF.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
That's 1.4159V P-P (assuming 50 Ohms :-( ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
Yup, that's been the standard combination for about that long. You also need wideband AGC, or else when the loop unlocks the gain will max out and the resulting distortion and noise intermod will prevent the loop from locking.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Wouldn't it be useful to have an analog version with an output voltage proportional to the phase difference?
Possibly. Usually a lock indicator is used to connect critically timed devices _after_ lock is assured. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
What I'm thinking about is that lock is never perfect, so in your circuit there the NOT gates are required to have just the right speed to indicate the amount of phase error you're looking for. But if there was an analog output you could monitor it for exactly the max error you want.
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