Detecting the peak value
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From: Jim Thompson on 29 Jul 2010 18:50 On Fri, 30 Jul 2010 07:29:03 +1000, Grant <omg(a)grrr.id.au> wrote: >On Thu, 29 Jul 2010 12:01:20 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: > >> >> >>Hi, >>Thanks for your response. I need analog or digital solution to >>implement it. I have doe search on peak detector on the internet and >>found many circuits. But I need something that can do what I mentioned >>in the diagram. Ideally with out those capacitor and resistor. If you >>can direct me in correct way than I wil be thankful. > >Also see my post in reply to Jim T. > >You can do it in software, but not easily for 100kHz. That's >need DSP techniques, I think? > >You just want to follow the peak voltage, there's lots of peak >detector circuits out there, in the opamp circuit collections, >say AN31 from national for starters, application notes from >other manufacturers too. > >Need the cap to hold the peak voltage, resistor across it to define >droop rate, duplicate the circuit upside down to follow negative >peaks. > >What you want to do with the output? > >Grant. I gather that the OP wants a "transition" at the peak. "It's beginning to sound a lot like..." homework :-) ...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 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: Grant on 29 Jul 2010 18:54 On Thu, 29 Jul 2010 15:50:17 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Fri, 30 Jul 2010 07:29:03 +1000, Grant <omg(a)grrr.id.au> wrote: > >>On Thu, 29 Jul 2010 12:01:20 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >> >>> >>> >>>Hi, >>>Thanks for your response. I need analog or digital solution to >>>implement it. I have doe search on peak detector on the internet and >>>found many circuits. But I need something that can do what I mentioned >>>in the diagram. Ideally with out those capacitor and resistor. If you >>>can direct me in correct way than I wil be thankful. >> >>Also see my post in reply to Jim T. >> >>You can do it in software, but not easily for 100kHz. That's >>need DSP techniques, I think? >> >>You just want to follow the peak voltage, there's lots of peak >>detector circuits out there, in the opamp circuit collections, >>say AN31 from national for starters, application notes from >>other manufacturers too. >> >>Need the cap to hold the peak voltage, resistor across it to define >>droop rate, duplicate the circuit upside down to follow negative >>peaks. >> >>What you want to do with the output? >> >>Grant. > >I gather that the OP wants a "transition" at the peak. > >"It's beginning to sound a lot like..." homework :-) > > ...Jim Thompson Maybe it's related to previous query? That's why I like to get an idea of where and why these things wanted. Difficult to offer specific help when an adjacent whatsit might be capable of doing half the job, or something. Grant.
From: krw on 29 Jul 2010 19:01 On Thu, 29 Jul 2010 12:48:50 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >Hi, > >Can you give some advice about how to use tracking A/D option to do >this? Disable the down input to the counter so it can only count "up". The A/D will follow the signal up, and then stay there; at the peak. If the counter only has a clock and direction, connect the counters "direction" to the count enable and the direction input to "up".
From: Jim Thompson on 29 Jul 2010 19:13 On Fri, 30 Jul 2010 08:54:12 +1000, Grant <omg(a)grrr.id.au> wrote: >On Thu, 29 Jul 2010 15:50:17 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Fri, 30 Jul 2010 07:29:03 +1000, Grant <omg(a)grrr.id.au> wrote: >> >>>On Thu, 29 Jul 2010 12:01:20 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >>> >>>> >>>> >>>>Hi, >>>>Thanks for your response. I need analog or digital solution to >>>>implement it. I have doe search on peak detector on the internet and >>>>found many circuits. But I need something that can do what I mentioned >>>>in the diagram. Ideally with out those capacitor and resistor. If you >>>>can direct me in correct way than I wil be thankful. >>> >>>Also see my post in reply to Jim T. >>> >>>You can do it in software, but not easily for 100kHz. That's >>>need DSP techniques, I think? >>> >>>You just want to follow the peak voltage, there's lots of peak >>>detector circuits out there, in the opamp circuit collections, >>>say AN31 from national for starters, application notes from >>>other manufacturers too. >>> >>>Need the cap to hold the peak voltage, resistor across it to define >>>droop rate, duplicate the circuit upside down to follow negative >>>peaks. >>> >>>What you want to do with the output? >>> >>>Grant. >> >>I gather that the OP wants a "transition" at the peak. >> >>"It's beginning to sound a lot like..." homework :-) >> >> ...Jim Thompson > >Maybe it's related to previous query? That's why I like to get an >idea of where and why these things wanted. Difficult to offer >specific help when an adjacent whatsit might be capable of doing >half the job, or something. > >Grant. Possibly. That's why I broached the all-pass 90� shift as another method. ...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 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: John Fields on 30 Jul 2010 06:20
On Thu, 29 Jul 2010 12:38:12 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >This seems to work pretty well... > >http://analog-innovations.com/SED/PeakFinder_2.pdf > >"U1" is a comparator. > > ...Jim Thompson --- Clever devil! :-) I don't know why, but a tracking ADC didn't even come to mind until you mentioned it. Old-timer's disease setting in maybe. :-( Anyways, what I was thinking about was more like a counter chain gated by a dflop clocked by a zero-crossing detector to get the period of the AC signal, then taking that quantity, shifting it one bit toward the LSB and counting it down to zero, using the same clock that drove the up-counter to get a half-period which would correspond to the location of the peak when the counter got to zero. Needs a little more thought to make sure both halves of the AC signal would be used to generate a continuous output in quadrature with the input, but I'm waiting for the OP to come back with his accuracy requirements before I put much more time into it. Nice thing about this circuit (if it's done right) is that, like a tracking ADC, it'll track the input and make edges which will follow the variations in its period. On the other hand, If he wants to use an ADC and he wants be able to place the edges with an accuracy of one degree at the peaks he'll need a 14 bit ADC, since if: E (sin 90�) = 1V then E (sin 89�) = 0.99985V and DV = 0.00015V, which is 1.5 parts in 10000. The best you can do with a 13 bit ADC is 1 part in 8192, so that won't work, but 14 bits is 1 part in 16384, so that will. For 1� resolution he'll need to sample 360 times in one cycle which comes out to 36Ms/s, which is certainly doable: http://focus.ti.com/lit/ds/symlink/ads6142.pdf |