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PLL Lock to an Offset Frequency

Jim, with all due respect, you need to think about what I wrote in my original post. The sign of the loop gain is opposite for USB and LSB for a given PD null, i.e. if you use an XOR or a diode mixer whose nulls are at quadrature, if the loop wants to lock up at +pi/2 on USB, it'll lock up at -pi/2 on LSB. With a PFD, one sideband will have the right sign of loop gain to lock up at 0, where (as you point out) everything is copacetic.

The point I was making in my original post is that the other sideband will have to try locking up at +- pi, where there's a ruddy great cliff--its PD gain there is like Vdd /2*pi*(f_0*t_PD), i.e. something like 500 times larger than the other null. Of course it's noisy and possibly metastable there, but the point is that the loop gain is _huge_, so no lock will occur there. Thus with a tiny bit of acquisition aiding, e.g. 2 resistors and a cap in positive FB around the loop amplifier, you can make a reliable lock to one sideband and not the other, _without_needing_a_SSB_mixer_.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs
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[snip]

OK. Now I follow you. Somehow I missed the "offset loop".

I like it!

I've seen similar things done using a D-Flop as a harmonic mixer.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Forget it. Other people understood.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

Phil,

The more I study your scheme the more I like it! I have a 1056MHz ±

132MHz situation that would be a perfect application of your configuration, because it's clearly superior for high ratios of carrier to offset.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Dividing down real-world signals is fine, as long as they are squeaky clean. Phase-locked loops can act like flywheels, filtering out occasional spikes and ringing artefacts, which can do nasty things to the counter doing the divide-by-640.

That's his example, not his problem - which he hasn't revealed.

Again, we don't know what he is really trying to do. ____________ Bill Sloman, Nijmegen

Reply to
bill.sloman

It was a fruitful post. From Phil Hobbs I gained an idea I really should have known.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

schreef in bericht news: snipped-for-privacy@g47g2000cwa.googlegroups.com...

Why would you want to do that? Divide the 8MHz by 640 and use that as your new reference.

We only know that the input frequency is 8MHz. That's as absolute as it comes, and 1/64th of it is therefore an absolute 125KHz.

[snip] 
--
Thanks, Frank.
(remove \'q\' and \'.invalid\' when replying by email)
Reply to
Frank Bemelman

Perhaps we were starting from different points.

Instead of using a SSB mixer, use an offset PLL as suggested by the OP, running at 1:1. This is an alternative to the 64x PLL with the 125-kHz reference frequency, that avoids the phase noise penalty of frequency multiplication (in this case, 20*log(64) or 36 dB). Something like this:

USB/LSB----------------------------------------------+ | | |

125 kHz ref--------------------------------+ | | | _V___ _V__ 8 MHz carrier------\\\\---\\ RC=700 ns | | | X | )) >---RRRR---+--->| PFD |---| +-1|---------+ +-//---/ | |_____| |____| | | R | (xor) CCC R | | +-CCC--RRR--+ R | GND ___ | /| | | | / \\ | /-|----+---+ +-----------
Reply to
Phil Hobbs

Finals week again?

Good Luck! Rich

Reply to
Rich Grise

Whoa, dood! You _ARE_ old! In 1973 I was getting laid and smoking Thai Stick. ;-P (not necessarily simultaneously, but usually. ;-P )

Cheers! Rich

Reply to
Rich Grise, Plainclothes Hippi

I was 33 and already had 4 kids.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

OK, I can live with this.

Frankly, I'd say it's just _one_ of the great things about s.e.d, not the least of which is, the people here are probably the smartest on the planet, and they have a sense of humour!

Ever checked out comp.lang.c ? Boy! Talk about a bunch of prigs! ;-)

Thanks, Rich

Reply to
Rich Grise

Nonsense! The classic condom has been around forever, you could even buy 'em in Massachusetts (under the counter), and diaphragms and birth control pills were already in use.

We had two girls and then I decided I'd like two boys.

Besides the dirt bag liberal weenies were already in motion trying to restrict birth rate. Remember Paul Erlich and his multiple appearances on The Tonight Show, touting Zero Population Growth (ZPG)?

So I decided SOMEONE had to keep conservatism going ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

and thats the great thing about SED.

Cheers Terry

Reply to
Terry Given

In those days Catholicism was indistinguishable because effective birth control was just catching on.

Dunno, just an observation.

Reply to
xray

Yes, I've done that back in the palmy days--about 1982, in my first engineering job (me with my new astronomy B. Sc.), I had to design and prototype a pilot tone generator at 70 +- (10/22) MHz--i.e.

70.45454545... and 69.54545454... MHz, don't ask me why, I didn't design the frequency plan. IIRC I used a 74LS293 as a divide-by-11 on the 10 MHz reference signal (jam reset on 12-count) followed by a divide-by-two to get 50% duty cycle, and clocked both halves of a 74S74 with the same 10 MHz. Those were the harmonic mixers for two offset 1:1 PLLs at 454.5... kHz, using Mini-Circuits RPD-1 diode bridge phase detectors, rather than PFDs. I really liked RPD-1s, because you got about a volt out of them, and they were really quiet.

The S74 output was very noisy due to metastability--the trailing edge jitter was especially non-pretty, and once in awhile it missed a pulse. I got round this by using a homemade VCXO on each side, and keeping the loop BW small. This was okay for this board, since the difference between the two pilot tones was going to be frequency-multiplied and used as the frequency reference for a 14 GHz direct-broadcast satellite system, and the PTG only had to be in the base station, not the remotes. (I think this was the first commercial DBS ever--it went on sale in early 1984.)

The spectrum analyzer trace of the signal from that S74 harmonic mixer was not a pretty sight--it jiggled around like a water fountain. I certainly wouldn't use that technique again--XORs work as harmonic mixers too, though you don't get the same signal amplitude of course.

It may be that using more recent logic parts and choosing the locking phase very carefully would keep the metastability under control better than I was able to do. As an 10:1 harmonic mixer at 70 MHz, the edges were just too close together for STTL.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

Brain fart. 7:1.

Reply to
Phil Hobbs

I built a circuit similar to this a long time ago using a 40 MHz carrier and a variable input of 10 KHz to 5 MHz, producing a 40.01 to 45 MHz output.

I used a MC10131 as a digital mixer instead of an xor gate. I used the MC12040 as the PFD. I added a 2nd MC12040 across the MC10131 to avoid lock-up in case the VCO frequency dipped below 40 MHz.

Daniel Lang

Reply to
Daniel Lang

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