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PLL Terminology Question

P = proportional PI = proportional-integral PID = proportional-integral-derivative

Eric Jacobsen Anchor Hill Communications

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Eric Jacobsen
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It is. Read Gardner. ...Jim Thompson

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| 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.
Reply to
Jim Thompson

Yup, that's how I learned it at the knee of a master of the art, back in about 1982. First order = no loop filter, or at least no loop filter poles below omega = Kvco*Kphi.

Second order loop = lead/lag integrator

Third order loop = two lead/lag integrators plus some analogue switches to prevent it from oscillating during acquisition.

A second order loop with extra poles out past the unity gain cross to help with the ripple rejection is still considered a second order loop.

Gardner talks about third order loops being used to get rid of static phase error due to linear frequency chirp, e.g. in satellite receivers. Since high-order loops are squirrelly, and a small constant phase error is easy to get rid of in software, even for an analogue loop, I sort of doubt anybody does that nowadays.

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
Reply to
Phil Hobbs

Can't remember the company name now, but it was in El Monte, CA (*), (~1967-68) where I was demo-ing my first analog phase detector and VCM combo detecting TACAN signals buried in noise. The company consultant was none other than Gardner himself, who first declared that my circuit couldn't be working... then had to reverse himself ;-)

(*) Quite a hilarious trip, after we survived. I was there with a Motorola salesman. An employee of the company offered to drive us back to the airport. On the way, his car battery bracket failed and dumped the battery out onto the freeway. CHIPs comes along and tickets him for impeding traffic :-)

We hail a cab. Cabby is a chatty Cathy and, while turned toward us in the back seat, rear-ends a car in the airport exit lane.

We hail another cab and finally make it to the airport.

Chatty Cathy cabby has the gall to contact us at Motorola and ask us to support his claim that rear-ending wasn't his fault ;-) ...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.
Reply to
Jim Thompson

ttdesign.com

Nice thread, thanks Tim.

I assume "Phaselock Techniques" by Flyod M. Gardener is the right book. (Making my Xmas wish list.) Any advantage of the third edition over the second?

So in a type III system the error signal is integrated twice? Does anyone have an example where double integration is used? It doesn't have to be a PLL application any type of control loop would be fine.

George H.

Reply to
George Herold

Software

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The extra filter/integrator is usually placed above the zero dB cross-over, just to reduce noise. ...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.
Reply to
Jim Thompson

Yes. You PLL guys are using "order" for "type". In control systems terms, the order of a system is the order of the system polynomial: so a PLL that has a PI + lowpass loop filter would be a 3rd-order control loop (because the lowpass adds a pole to the system), but it would remain a type 2 system (because the lowpass filter does not have infinite gain at DC). Presumably, in PLL terms it would be correct to call it "2nd-order"

-- but that makes me want to gag!

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

Both the number of poles (order), and the number of nekkid integrators (type) have relevance in telling you how the loop is going to behave.

It's not obscurity if you know what it means.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

For any control loop you pick a point in the loop and go around, counting integrators, until you get back to the same point. Because the VCO takes a voltage and turns it into a frequency (which is the integral of phase), and because a phase detector detects _phase_, the VCO-phase detector combination will always come up acting like an integrator.

If you use a frequency detector instead of a phase detector, then you cannot treat the VCO as an integrator for the purposes of loop analysis, or you have to treat it as an integrator followed by a perfect differentiator.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

Perhaps Hoffman Electronics of El Monte, CA, now known as Navcom Defense Electronics of Corona, CA?

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

I don't think there's a disconnect. A 2nd-order loop has degree two in the denominator polynomial, and are typically implemented with two integrators (including the NCO). It is also possible to implement a

2nd-order loop with three integrators, but this is seldom done (unless it's an FLL).

Eric Jacobsen Anchor Hill Communications

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Reply to
Eric Jacobsen

I've done it with gyroscopically stabilized platforms -- leave out the second integrator and when you (or the world) pushes on it it moves over and stays there until the push is gone. Put the second integrator in and it pushes back until it's in place.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

Yep, That was it! Thanks! ...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.
Reply to
Jim Thompson

Well yes, in essence that's what I said. We know what the poles and zeroes do. Introducing superfluous terminology like 'type' does not make it any clearer. I'd say: Drop the type.

Right.

Jeroen Belleman

Reply to
Jeroen

Poles are from Poland. What are zeroes? Larkin ?>:-) ...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.
Reply to
Jim Thompson

Harumph! Flub, phase is the integral of frequency. But you know that, of course.

Jeroen Belleman

Reply to
Jeroen

A type 0 loop can have a bazillion poles and still be type 0.

A type 2 loop can have only two poles.

Poles and type are _different_.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

Blargh. Indeedie.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com
Reply to
Tim Wescott

Zeroes were manufactured by Mitsubishi.

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Reply to
Jasen Betts

Software

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No, it's another lead-lag integrator, to reduce the static phase offset due to a frequency ramp to zero. Back in the all-analogue days, that sometimes mattered.

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
Reply to
Phil Hobbs

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