Detecting the peak value
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From: john1987 on 29 Jul 2010 16:32 Hi, Can you suggest any part number? Thanks John
From: whit3rd on 29 Jul 2010 16:35 On Jul 29, 10:17 am, john1987 <conphil...(a)hotmail.com> wrote: > I built the circuit that can detect the peak of the 100KHz , 2 Volts > peak to peak sine wave but its not accurate... > I do require the edge to occur as close as possible to the sine wave > positive and negative peaks. The peak of a sinewave is a point at which the time-change behavior is minimum; timing on a peak detector is ALWAYS dealing with noise against a small signal (because there's small time dependence at that part of the waveform). For accuracy, you need to use a phase-locked loop or some other history-sensing technique, detecting not just the peak behavior but sensitive to the waveform before that peak. Either an integrator or differentiator circuit can help, and bandwidth limiting filtration is also useful. Note especially that op amp distortion sometimes causes either the zero-crossing (with resistive load) or peak (with capacitive load) points to be poorly characterized. If your source is a push-pull amplifier, it matters a lot how you load it.
From: SilverLeo on 29 Jul 2010 16:54 Il Thu, 29 Jul 2010 10:17:29 -0700, john1987 ha scritto: > 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 > http://a.imageshack.us/img829/6505/161639.jpg It sounds to me more like an "edge detector", not a peak detector. Actually I reverse engineered an old barcode reader that used exactly the same circuit. R and C values were tuned to get the right amount of phase shift (at a given scanning rate) needed by comparator to get its job done. Output pulses were feed to a timer/counter. Track and hold is a better way to design a peak detector.
From: john1987 on 29 Jul 2010 17:03 Thanks for the replies. Are track and hold circuits available as chips that I buy or I have to build one. How does the block diagram of the circuit look like? John
From: John Fields on 29 Jul 2010 17:19
On Thu, 29 Jul 2010 14:03:27 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >Thanks for the replies. Are track and hold circuits available as chips >that I buy or I have to build one. How does the block diagram of the >circuit look like? --- First things first. How accurate do you need this thing to be? |