Detecting the peak value
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From: Jim Thompson on 30 Jul 2010 10:46 On Fri, 30 Jul 2010 07:34:56 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >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. > >What's wrong with an RC? > >Actually, and RC doesn't approach the required 90 degree lead or lag >unless the time constant is huge, and then the signal is approaching >zero. If your signal frequency is fairly steady, an R-L-C can do a lot >better. > >Try this: > > >in-------R------L---+------------comparator+ > | > | > C > | > +------------comparator- > | > | > gnd > > >Pick the R-C to give, say, 70 degrees of lag at 100 KHz. Pick the L to >add phase lag until the comparator switches just at the signal peaks, >compensating for comparator delay while you're at it. R can be partly >trimpot for fine tuning. This will preserve a healthy fraction of the >original signal amplitude. > > >I've also done this as > >in-------C----------+------------comparator+ > | > | > R > | > L > | small > | offset---comparator- > | > | > gnd > >as a fast constant-fraction discriminator, with an ecl comparator, >instead of the usual delay-line thing. > >John > john1987 is invited to do the math. A differentiator finds peaks just fine as previously demonstrated, and a 90� all-pass is also trivial, without an inductor, also as previously demonstrated. ...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: Phil Hobbs on 30 Jul 2010 10:53 john1987 wrote: > Hi, > > The accuracy requirements are as follows > > 1. The frequency of the sine wave is 100 kHz. +/- 3us > 2 The amplitude is 2 volts peak to peak, it should be accurately > measured at +/- 1.9 volts. > Its not a home work. :) > > > Thanks > > John > > > That sounds like a job for a window comparator. All these peak detector gizmos are assuming you don't know the actual amplitude. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Jim Thompson on 30 Jul 2010 11:02 On Fri, 30 Jul 2010 10:53:38 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >john1987 wrote: >> Hi, >> >> The accuracy requirements are as follows >> >> 1. The frequency of the sine wave is 100 kHz. +/- 3us >> 2 The amplitude is 2 volts peak to peak, it should be accurately >> measured at +/- 1.9 volts. >> Its not a home work. :) >> >> >> Thanks >> >> John >> >> >> > >That sounds like a job for a window comparator. All these peak detector >gizmos are assuming you don't know the actual amplitude. > >Cheers > >Phil Hobbs (1) Differentiator + Comparator: NO (2) All-pass + Comparator: NO (3) Tracking ADC/Counter: NO How does a window detector find "peak"? It can find zero-crossings just ducky, but not "peak"... unless you "know actual amplitude" :-) ...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: Tim Wescott on 30 Jul 2010 11:04 On 07/29/2010 12:03 PM, john1987 wrote: (Could you please include context in your replies? This is USENET.) > 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. Why are you dead set against the RC circuit? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Tim Wescott on 30 Jul 2010 11:05
On 07/29/2010 12:03 PM, john1987 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. > Detecting peaks requires memory of past history of the wave, which means (in an analog circuit) than you need a capacitor or an inductor. So, sure you can get rid of the cap -- if you don't mind having an inductor in there. People keep asking you questions like "is your frequency stable", trying to find ways to make you happy, and you keep responding with "I don't even want to put up with a capacitor in my circuit". What are you really trying to do, and what are your real constraints? What's the matter with a cruddy capacitor? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |