Detecting the peak value
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From: Grant on 29 Jul 2010 17:21 On Thu, 29 Jul 2010 12:00:26 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Thu, 29 Jul 2010 10:17:29 -0700 (PDT), john1987 ><conphiloso(a)hotmail.com> wrote: > >>Hi, >> >>I built the circuit that can detect the peak of the 100KHz , 2 Volts >>peak to peak sine wave but its not accurate or may be not working >>right. >>The problems seem to be choosing the right R and C values. Is there >>any way that I can do this with out using a Capcitor and a resistor >>and if not than whats the best possible way to choose the R and C >>values. >> >>I do require the edge to occur as close as possible to the sine wave >>positive and negative peaks. >> >>I used Low Pass filter. you can find the diagram of the circuit and >>the waveform at the following links. >> >>http://a.imageshack.us/img651/6509/161617.jpg That's not peak detector, it's the classic data recovery where chop level follows average signal DC level. >> >>http://a.imageshack.us/img829/6505/161639.jpg >> >> >> >>Thanks >>John > >Reading more carefully :-( > >You really are after a peak "finder". > >So use a differentiator and run the result thru a comparator... >current in differentiating capacitor reverses at the peak. Use it to sample the peak, perhaps that's what you meant? > >OR... > >If frequency is stable, use the all-pass I recently posted to get an >accurate 90° phase shift, then thru a comparator. > >Fields idea sounds good too... I'm guessing use a tracking A-to-D and >watch for count direction reversal?? Yes, take previous sample when current sample is lower absolute value, common thing working with sampled data. Once detected peak, rearm the peak detector for next cycle. Sometimes you need to qualify the peak if there's noise coming in. Grant.
From: john1987 on 29 Jul 2010 17:26 Hi, +/- 10 % thanks John
From: Grant on 29 Jul 2010 17:29 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.
From: Grant on 29 Jul 2010 17:30 On Thu, 29 Jul 2010 12:03:46 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >I think that I am doing what are suggesting to use the differeniator. >But is there another analog way to do it meant without using the RC >circuit. Sample / hold with differentiator to drive it to sample the peak.
From: whit3rd on 29 Jul 2010 18:21
On Jul 29, 2:26 pm, john1987 <conphil...(a)hotmail.com> wrote: > Hi, > > +/- 10 % > > thanks > John Ten percent of what? The cycle time of a 100 kHz sinewave is 10 us, do you mean +/- 1 us? Or the peak value is 2V, and you need to detect at or above 1.8V (that'd be plus/minus 25 degrees)? Is the frequency fixed and accurate at 100 kHz? Is the amplitude fixed and accurate at 2V? If amplitude varies, a phase-locked loop or phase-shift network is preferred. If frequency varies, an integrator or differentiator will be better than an RC phase shifter. will be preferred. If both are |