PLL for Zero Delay LPF
in [Design]
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From: Glenn Kenroy on 23 Jun 2010 05:09 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. Glenn Kenroy ****** "The first step is to make a PLL that locks onto the 60Hz. You want the VCO in the PLL to be running at many times the 60Hz frequency. I am going to suggest 7200 times, but faster is likely better. 7200 times just makes the explanation easier. Important frequencies: 60*8*3*5 = 7200 7200 / 15 = 60*8 7200 / 3 = 5*60*8 7200 / 5 = 3*60*8 I will assume that you have the PLL locked to the 60Hz. You will be making the same circuit 3 times. It uses the CD4051 The 8 times the frequency goes to a counter that makes the CD4051 scan through a group of capacitors. Each of the 8 outputs of the CD4051 connects to one end of a capacitor. The other end of the capacitor is grounded. If the common point is fed with a resistor. This makes a circuit that will charge up the capacitors until they match the 60Hz input waveform." ******
From: Jim Thompson on 23 Jun 2010 10:38 On Wed, 23 Jun 2010 09:09:51 GMT, glennkenroy(a)protech.com (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. > >Glenn Kenroy > >****** > >"The first step is to make a PLL that locks onto the 60Hz. You want >the VCO in the PLL to be running at many times the 60Hz frequency. >I am going to suggest 7200 times, but faster is likely better. 7200 >times just makes the explanation easier. > >Important frequencies: > >60*8*3*5 = 7200 > >7200 / 15 = 60*8 >7200 / 3 = 5*60*8 >7200 / 5 = 3*60*8 > >I will assume that you have the PLL locked to the 60Hz. > >You will be making the same circuit 3 times. It uses the CD4051 >The 8 times the frequency goes to a counter that makes the >CD4051 scan through a group of capacitors. > >Each of the 8 outputs of the CD4051 connects to one end of >a capacitor. The other end of the capacitor is grounded. > >If the common point is fed with a resistor. This makes a circuit >that will charge up the capacitors until they match the 60Hz >input waveform." > >****** As I demonstrated in... "ANALYSIS AND DESIGN OF INTEGRATED CIRCUITS" MOTOROLA Series in Solid-State Electronics �1967 Library of Congress Catalog Card Number: 66-25486 Chapter 15 (Which I wrote :-) pp470-473 ...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: George Jefferson on 23 Jun 2010 10:49 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:tl6426p5j5krd74544t873c85p1e9dp55f(a)4ax.com... > On Wed, 23 Jun 2010 09:09:51 GMT, glennkenroy(a)protech.com (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. >> >>Glenn Kenroy >> >>****** >> >>"The first step is to make a PLL that locks onto the 60Hz. You want >>the VCO in the PLL to be running at many times the 60Hz frequency. >>I am going to suggest 7200 times, but faster is likely better. 7200 >>times just makes the explanation easier. >> >>Important frequencies: >> >>60*8*3*5 = 7200 >> >>7200 / 15 = 60*8 >>7200 / 3 = 5*60*8 >>7200 / 5 = 3*60*8 >> >>I will assume that you have the PLL locked to the 60Hz. >> >>You will be making the same circuit 3 times. It uses the CD4051 >>The 8 times the frequency goes to a counter that makes the >>CD4051 scan through a group of capacitors. >> >>Each of the 8 outputs of the CD4051 connects to one end of >>a capacitor. The other end of the capacitor is grounded. >> >>If the common point is fed with a resistor. This makes a circuit >>that will charge up the capacitors until they match the 60Hz >>input waveform." >> >>****** > > As I demonstrated in... > > "ANALYSIS AND DESIGN OF INTEGRATED CIRCUITS" > MOTOROLA Series in Solid-State Electronics > �1967 Library of Congress Catalog Card Number: 66-25486 > > Chapter 15 (Which I wrote :-) pp470-473 > Jim, can I get a list of everything you have ever done so I can see just how omnipotent you really are?
From: Vladimir Vassilevsky on 23 Jun 2010 11:03 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. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: John Larkin on 23 Jun 2010 11:12
On Wed, 23 Jun 2010 09:09:51 GMT, glennkenroy(a)protech.com (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. > >Glenn Kenroy > >****** > >"The first step is to make a PLL that locks onto the 60Hz. You want >the VCO in the PLL to be running at many times the 60Hz frequency. >I am going to suggest 7200 times, but faster is likely better. 7200 >times just makes the explanation easier. > >Important frequencies: > >60*8*3*5 = 7200 > >7200 / 15 = 60*8 >7200 / 3 = 5*60*8 >7200 / 5 = 3*60*8 > >I will assume that you have the PLL locked to the 60Hz. > >You will be making the same circuit 3 times. It uses the CD4051 >The 8 times the frequency goes to a counter that makes the >CD4051 scan through a group of capacitors. > >Each of the 8 outputs of the CD4051 connects to one end of >a capacitor. The other end of the capacitor is grounded. > >If the common point is fed with a resistor. This makes a circuit >that will charge up the capacitors until they match the 60Hz >input waveform." > >****** The commutating capacitor thing is cute, but it makes a bandpass filter, not a lowpass. And you'd get better signal quality using a commercial switched-capacitor filter, which can also be clocked by a PLL. Does your filter really need to be realtime? If you're acquiring and digitizing the data, it can be post-processed, which allows a near-ideal lowpass to be applied. A zero delay realtime lowpass filter is impossible. John |