PLL for Zero Delay LPF
in [Design]
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From: Joerg on 23 Jun 2010 11:16 Vladimir Vassilevsky wrote: > > > Glenn Kenroy wrote: > >> Excuse me for resuscitating this topic, but I was wondering if anyone >> could elaborate further on the following concept (see excerpt below) >> generously provided by MooseFET? >> My original post was about how to design a _zero_ delay LP filter for >> geomagnetic signals below 50Hz. >> I am hoping for a bit more detail to assist me in coming up with a >> workable schematic. > > You need to contact Harry Potter or some democrat, as they believe they > can make miracles. Several folks already explained why zero delay filter > is impossible. There is no way to make zero delay filter, although it is > possible to play different tricks with phase; PLL is one of those. > If someone came up with a negative delay filter, now that would be something :-) -- SCNR, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 23 Jun 2010 11:23 On Wed, 23 Jun 2010 08:16:30 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Vladimir Vassilevsky wrote: >> >> >> Glenn Kenroy wrote: >> >>> Excuse me for resuscitating this topic, but I was wondering if anyone >>> could elaborate further on the following concept (see excerpt below) >>> generously provided by MooseFET? >>> My original post was about how to design a _zero_ delay LP filter for >>> geomagnetic signals below 50Hz. >>> I am hoping for a bit more detail to assist me in coming up with a >>> workable schematic. >> >> You need to contact Harry Potter or some democrat, as they believe they >> can make miracles. Several folks already explained why zero delay filter >> is impossible. There is no way to make zero delay filter, although it is >> possible to play different tricks with phase; PLL is one of those. >> > >If someone came up with a negative delay filter, now that would be >something :-) Does the OP need zero delay or is it really _flat_phase_? It'd probably be a PITA, but I'd guess one could conjure up something like an all-pass to flatten the phase response. ...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 | Where is Joe McCarthy when you need him ??
From: Joerg on 23 Jun 2010 11:29 Jim Thompson wrote: > On Wed, 23 Jun 2010 08:16:30 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Vladimir Vassilevsky wrote: >>> >>> Glenn Kenroy wrote: >>> >>>> Excuse me for resuscitating this topic, but I was wondering if anyone >>>> could elaborate further on the following concept (see excerpt below) >>>> generously provided by MooseFET? >>>> My original post was about how to design a _zero_ delay LP filter for >>>> geomagnetic signals below 50Hz. >>>> I am hoping for a bit more detail to assist me in coming up with a >>>> workable schematic. >>> You need to contact Harry Potter or some democrat, as they believe they >>> can make miracles. Several folks already explained why zero delay filter >>> is impossible. There is no way to make zero delay filter, although it is >>> possible to play different tricks with phase; PLL is one of those. >>> >> If someone came up with a negative delay filter, now that would be >> something :-) > > Does the OP need zero delay or is it really _flat_phase_? > > It'd probably be a PITA, but I'd guess one could conjure up something > like an all-pass to flatten the phase response. > That used to be one of our regular chores in Doppler ultrasound. Gradually the required 1% capacitor became unobtanium and then, huge sigh of relief, AD came out with the first affordable DSP for around 10 bucks. Then, the folks in purchasing started to like us again and we could share in their Christmas time bonbon cartons they got from distributors. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Vladimir Vassilevsky on 23 Jun 2010 11:57 Joerg wrote: > Vladimir Vassilevsky wrote: > >> >>Glenn Kenroy wrote: >> >> >>>Excuse me for resuscitating this topic, but I was wondering if anyone >>>could elaborate further on the following concept (see excerpt below) >>>generously provided by MooseFET? >>>My original post was about how to design a _zero_ delay LP filter for >>>geomagnetic signals below 50Hz. >>>I am hoping for a bit more detail to assist me in coming up with a >>>workable schematic. >> >>You need to contact Harry Potter or some democrat, as they believe they >>can make miracles. Several folks already explained why zero delay filter >>is impossible. There is no way to make zero delay filter, although it is >>possible to play different tricks with phase; PLL is one of those. >> > > > If someone came up with a negative delay filter, now that would be > something :-) There was a good thread in comp.dsp about filters with negative dfi/dW, i.e. negative group delay. This is indeed possible. Those filters forecast the future by predicting the waveform, but they can't see into the future. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: Tim Wescott on 23 Jun 2010 12:12
On 06/23/2010 08:23 AM, Jim Thompson wrote: > On Wed, 23 Jun 2010 08:16:30 -0700, Joerg<invalid(a)invalid.invalid> > wrote: > >> Vladimir Vassilevsky wrote: >>> >>> >>> Glenn Kenroy wrote: >>> >>>> Excuse me for resuscitating this topic, but I was wondering if anyone >>>> could elaborate further on the following concept (see excerpt below) >>>> generously provided by MooseFET? >>>> My original post was about how to design a _zero_ delay LP filter for >>>> geomagnetic signals below 50Hz. >>>> I am hoping for a bit more detail to assist me in coming up with a >>>> workable schematic. >>> >>> You need to contact Harry Potter or some democrat, as they believe they >>> can make miracles. Several folks already explained why zero delay filter >>> is impossible. There is no way to make zero delay filter, although it is >>> possible to play different tricks with phase; PLL is one of those. >>> >> >> If someone came up with a negative delay filter, now that would be >> something :-) > > Does the OP need zero delay or is it really _flat_phase_? > > It'd probably be a PITA, but I'd guess one could conjure up something > like an all-pass to flatten the phase response. That's been suggested in the original thread. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com |