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Is this a PLL?

I've dealt with:

  1. "Regular" PLL's where there's a VCO and a phase detector and a loop filter and the frequency is slewed to phase-lock the VCO to a reference.

But I also occasionally deal with:

  1. Clock-recovery circuits that don't really have a variable-frequency oscillator. There is a clock, but it's fixed frequency and typically runs 8x or 16x (or sometimes more) higher than the data rate. There's a shift register and a clock-pulse recovery subcircuit, and the the shift register has its phase adjusted +/- a clock or two to keep the data separator locked to the data.

Is #2 a PLL? It is phase-locked, but doesn't really have a variable frequency that "remembers" the last time it was locked (in the absence of a data stream it ticks along solely according to the fixed-frequency clock without any adjustment).

I have sometimes seen things like #2 called a "digital PLL" but my gut feeling is to call it a "data separator".

And there's a third category:

  1. A digital PLL with a "numerically controlled oscillator", e.g. frequency really is being adjusted (not just phase), but it's all done with counters instead of a VCO.

Maybe #3 is a true "digital PLL".

Am I too picky about nomenclature?

Tim.

Reply to
Tim Shoppa
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I have seen #2 called a PLL -- I have even called #2 a PLL because I knew that calling it a "frequency locked loop" or a "automatic clock adjuster" would harvest me a bunch of confusion, and, when explained, an exasperated "well that's just a PLL!".

I certainly consider #3 to be a PLL.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott

So it's phase AND frequency locked.

I still call those PLL's or phase jerkers ;-) Very handy for systems with missing data transitions that ordinary PFD's throw up over.

Yes.

Picky is as picky does ;-)

...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

I like it. Succinct.

Tim.

Reply to
Tim Shoppa

I've used that scheme since the late '70's to lock to such intermittent data as, for example, floppies.

It will also lock to video that, for some reason, is missing some sync ;-)

...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 | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

Did you design the data separator in the WD floppy chip application notes? It's a phase jerker from around that time frame... (and sure beat the RC one-shots in the competition!)

Tim.

Reply to
Tim Shoppa

I designed the one for the GenRad PSP portable tester. I used to demo it by swinging the case around my head in all kinds of gyrations while it merrily kept on reading without error. It would withstand a huge speed variation without a problem.

I'll post it when I find a copy.

Found it! Watch for it on A.B.S.E

...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

See...

Newsgroups: alt.binaries.schematics.electronic Subject: Phase "Jerker" from S.E.D - FloppyClockRestore.pdf Message-ID:

...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

Quite possibly.

Delaying a clock by dQ every M cycles is the same as decreasing the frequency by a factor of M/(M+dQ). You can accomplish the same goal by dividing a clock (possibly with a different starting frequency) by N+1 instead of N.

You haven't provided any information about the rest of the system in #2 and #3, so it's not clear to me whether or not they're equivalent, but they certainly could be. By the same token, whether or not the output in #2 stops incrementing without data is a function of the loop architecture.

-- Mike --

Reply to
Mike

No, it makes a big difference in detecting data streams in noise. They are all PLL, with 1 being the best, then 3, and 2 is dependent upon F at transmit to be right on receive F, a weaker design. #1 may work in 5 dB SNR, #2 may require 20 dB SNR to work. Phase and frequency are not completely separable.

Reply to
night soil dalits

Working SNR depends on *type* of phase detector, band-limiting, etc.

...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

night soil dalits skrev:

2 works just fine for the majority of uarts and that's with transmit-recieve frequency differences in percent..

with a nco clocked fast enough compared to the output 3 could be just as good as 1, and could probably be made even better because you could add a much more intelligent detector/feedback algorithm...

-Lasse

Reply to
langwadt

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