On Oct 14, 8:39�pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
> On 10/14/2012 7:49 PM, George Herold wrote:
>
>
>
> > On Oct 14, 6:58 pm, Phil Hobbs
> > <pcdhSpamMeSensel...@electrooptical.net> wrote:
> >> On 10/14/2012 6:24 PM, George Herold wrote:
>
> >>> On Oct 14, 5:16 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> >>>> On Sat, 13 Oct 2012 18:10:49 -0700, George Herold wrote:
> >>>>> On Oct 13, 12:27 am, Tim Wescott <t...@seemywebsite.com> wrote:
> >>>>>> On Sat, 13 Oct 2012 00:01:00 +0200, Jeroen wrote:
> >>>>>>> On 2012-10-12 19:02, Tim Wescott wrote:
> >>>>>>>> On Fri, 12 Oct 2012 12:08:46 +0200, Jeroen Belleman wrote:
>
> >>>>>>>>> On 2012-10-12 11:04, Robert Baer wrote:
> >>>>>>>>>> Vladimir Vassilevsky wrote:
> >>>>>>>>>>> "Tim Wescott"<t...@seemywebsite.com> wrote:
> >>>>>>>>>>>> How commonly do you see PLL designs referred to as "type I",
> >>>>>>>>>>>> "type II", "type III", etc.? Do the terms make sense to you?
>
> >>>>>>>>>>> IMO this terminology is used only in Gardner's book; there is no
> >>>>>>>>>>> universal
> >>>>>>>>>>> meaning.
> >>>>>>>>>>> It is about P, PI, or PII control loop. Remnants of old times,
> >>>>>>>>>>> when they used to mix the details of implementation with the type
> >>>>>>>>>>> of the transfer function.
>
> >>>>>>>>>>>> I'm writing a report; don't want to either baffle with bullshit
> >>>>>>>>>>>> nor leave
> >>>>>>>>>>>> out handy terms...
>
> >>>>>>>>>>> Since nobody is going to read it anyway, why would that matter?
>
> >>>>>>>>>>> Vladimir Vassilevsky
> >>>>>>>>>>> DSP and Mixed Signal Consultant
> >>>>>>>>>>>www.abvolt.com
>
> >>>>>>>>>> Do not know but my wild uneducated guess is that "P" stands for
> >>>>>>>>>> regular feedback as in a standard op-amp circuit, "PI" stands for
> >>>>>>>>>> first derivative (eg: "P dot") and "PII" stands for second
> >>>>>>>>>> derivative (eg: "P double dot").
>
> >>>>>>>>> 'I' stands for an Integral term, not a derivative one.
>
> >>>>>>>>> I think that PLL designs should be classified by the number of
> >>>>>>>>> significant poles and zeroes of their transfer functions. This
> >>>>>>>>> 'type' business only introduces an extra layer of obscurity.
>
> >>>>>>>> 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.
>
> >>>>>>> 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.
>
> >>>>>> 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 &
> >>>>>> Softwarehttp://www.wescottdesign.com-Hidequotedtext -
>
> >>>>>> - Show quoted text -
>
> >>>>> OK Well I thought I was getting the type 'thing', but I'm confused
> >>>>> again.
>
> >>>>> First what's type zero?
> >>>>> I was thinking about a (type I?) loop with just gain control that I've
> >>>>> used to lock a diode laser to the side of an absorption line. �You've
> >>>>> got to put a (single pole) lowpass between the error signal and the
> >>>>> gain, or it's pretty much an oscillator.
>
> >>>>> George H.
>
> >>>> Type 0 is a loop that has no naked integrators (a low-pass isn't
> >>>> considered a naked integrator in this context, as it has finite DC gain).
>
> >>>> --
> >>>> 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 & Softwarehttp://www.wescottdesign.com-Hidequoted text -
>
> >>>> - Show quoted text -
>
> >>> Hmmm OK, �For the diode laser locking thing, the piezo (plant) has a
> >>> resonance a bit above 3kHz. �Say I use a low pass filter with a 1
> >>> second time constant, and then crank up the gain til it's just below
> >>> the oscillation point.... how 'naked' does the integrator need to be?
> >>> (would 10 seconds and more gain count?)
>
> >>> George H.
>
> >> If you put in a notch filter, you can get the loop BW a lot closer to
> >> the piezo resonance, like 0.3 f_0 vs 0.03 f_0.
>
> >> 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 USA
> >> +1 845 480 2058
>
> >> hobbs at electrooptical dot nethttp://electrooptical.net-Hide quoted text -
>
> >> - Show quoted text -
>
> > Grin, �OK I'm not saying that a single pole low pass and then gain, is
> > in any way optimal. �But it works... is it type 0 or type I?
>
> > (Does notching out the piezo resonace work? �I've never tried that.)
>
> > George H.
>
> Notching works great, if the resonator Q is high. �The notch filter's
> phase shift goes away on the scale of its bandwidth rather than its
> centre frequency, so it has almost no effect beyond a few times delta-f.
>
> In my atomic force microscope days, I used that trick to get a factor of
> 10 in loop bandwidth with a piezo bimorph whose Q was right around 30.
>
> 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 USA
> +1 845 480 2058
>
> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>
> - Show quoted text -
Cool thanks, I don't know the Q, but I'd guess it's above 10.
A multi layer stack from a Japanesse company whose name is escaping me
now...
(~4 um at 100V with a SRF of ~400kHz.)
Driving an Al (7075) flexure with a grating attached.
It'd be nice to get above 3kHz since there's still mucho vibrations
up there.
(This is a bit of a 'throw away' part of the diode laser, it's mostly
a student insturment and they're happy to get it tuned
to an Rb line and see the SAS.)
George H.