Detecting the peak value
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From: Grant on 2 Aug 2010 03:17 On Sun, 01 Aug 2010 23:35:21 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 30 Jul 2010 07:28:22 -0700 (PDT), john1987 ><conphiloso(a)hotmail.com> 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 >> >+/- 3 uS out of 5 uS (for a half cycle) is pretty sloppy. A constant >delay filter of 100 nS and a comparator will yeild much better >results. > > |\ > signal --------+------------------|+\ > | | \ > | | \ > | | >--------- out > | | / > + (| 100 nS)------|- / > | / > |/ > >Bias etc., ommited. > >Somewhat subject to high frequency noise and amplitude wobble. >Typically withing a few degrees. Forgive me being pedantic, but do you want little 's' for seconds above, rather than big 'S' for Siemens(sp?) (which I never did quite figure out, umho or something warpedly related to ohms?) Grant.
From: Jim Thompson on 2 Aug 2010 11:01 On Sun, 1 Aug 2010 15:29:19 GMT, hal(a)nospam.com wrote: >Hello all, > >I've been following this thread and it has brought up some issues I'm >currently working on. First of all, I'm a hobbyist that likes to learn by >doing; as such, I'm interested in making a circuit do what I want without >regards to a BOM - especially in regards to performance. In other words, I >like "best" rather than "cheapest" or "easiest." > >Currently I'm working on a LCR meter for personal use with better than .1% >accuracy (closer to .02% if possible) for all functions. Also, all >calibration will be internal and automatic; I have quite a few of Vishay's >S102C series resistors (.01%, 2ppm) so I have a ready internal reference to >use, keeping all measurements ratiometric if possible, and use resistance as >the "known" in all equations. > >I'm measuring capacitance using constant-current charge time, so I already >will know the capacitance before I measure the ESR and can account for Z. I >originally planned to use a peak-detection (measurement) scheme with a >100khz low distortion sine wave, however 1-2% accuracy was the best it >seemed that I could do (Yes, I realize that for ESR, that is good enough - >but remember, I'm doing this to learn and just to see if I can for the fun >of it). So, as it stands, I am planning on using a S/H or tracking ADC with >a high enough sample rate to detect both high and low peaks of both the DUT >and a reference resistance and calculate the ESR from there. > >As the required additional circuitry to measure the ESR is almost as much as >all of the rest put together, I can't help but wonder if there's an easier >way that I've missed and I'm using a sledge hammer to drive a nail. So, I >would welcome any suggestions, tips or hints. > >Thanks, > >Hal What I had in mind... http://analog-innovations.com/SED/CapacitorMeasurement.pdf Avoid the vagaries of a current source using only an OpAmp, a scaling resistor, and a reference source (the -2.5V). For you high current range simply add an NPN follower to the OpAmp. Note that you don't care about the offset of the OpAmp... it just needs to be fast enough to handle your fastest ramp. The offsets of the comparators _do_ matter. Maybe an auto zero function here? ...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: Jim Thompson on 2 Aug 2010 11:12 Corrections :-) On Mon, 02 Aug 2010 08:01:28 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Sun, 1 Aug 2010 15:29:19 GMT, hal(a)nospam.com wrote: > >>Hello all, >> >>I've been following this thread and it has brought up some issues I'm >>currently working on. First of all, I'm a hobbyist that likes to learn by >>doing; as such, I'm interested in making a circuit do what I want without >>regards to a BOM - especially in regards to performance. In other words, I >>like "best" rather than "cheapest" or "easiest." >> >>Currently I'm working on a LCR meter for personal use with better than .1% >>accuracy (closer to .02% if possible) for all functions. Also, all >>calibration will be internal and automatic; I have quite a few of Vishay's >>S102C series resistors (.01%, 2ppm) so I have a ready internal reference to >>use, keeping all measurements ratiometric if possible, and use resistance as >>the "known" in all equations. >> >>I'm measuring capacitance using constant-current charge time, so I already >>will know the capacitance before I measure the ESR and can account for Z. I >>originally planned to use a peak-detection (measurement) scheme with a >>100khz low distortion sine wave, however 1-2% accuracy was the best it >>seemed that I could do (Yes, I realize that for ESR, that is good enough - >>but remember, I'm doing this to learn and just to see if I can for the fun >>of it). So, as it stands, I am planning on using a S/H or tracking ADC with >>a high enough sample rate to detect both high and low peaks of both the DUT >>and a reference resistance and calculate the ESR from there. >> >>As the required additional circuitry to measure the ESR is almost as much as >>all of the rest put together, I can't help but wonder if there's an easier >>way that I've missed and I'm using a sledge hammer to drive a nail. So, I >>would welcome any suggestions, tips or hints. >> >>Thanks, >> >>Hal > >What I had in mind... > >http://analog-innovations.com/SED/CapacitorMeasurement.pdf > >Avoid the vagaries of a current source using only an OpAmp, a scaling >resistor, and a reference source (the -2.5V). > >For you high current range simply add an NPN follower to the OpAmp. ^^^--- your > >Note that you don't care about the offset of the OpAmp... Yes you do... accuracy of test current. (Or chopper-stabilized.) >it just >needs to be fast enough to handle your fastest ramp. > >The offsets of the comparators _do_ matter. Maybe an auto zero >function here? (Or chopper-stabilized.) > > ...Jim Thompson ...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: JosephKK on 2 Aug 2010 22:36 On Fri, 30 Jul 2010 14:28:46 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >On Jul 30, 5:16�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >Web-Site.com> wrote: >> On Fri, 30 Jul 2010 14:07:46 -0700 (PDT), john1987 >> >> <conphil...(a)hotmail.com> wrote: >> >Hi, >> >> >200pF and 82 ohm resistor gives me approximately 9 Mhz frequency and >> >its a high pass filter. SO, does it mean that filter will pass all the >> >frequncies less than 9MHz. >> >> >Thanks >> >John >> >> Stop snipping content and look at my drawing. >> >> � � � � � � � � � � � � � � � � � � � � ...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)460-2350begin_of_the_skype_highlighting��������������(480)460-2350������end_of_the_skype_highlighting�Fax: Available upon request | �Brass Rat �| >> | E-mail Icon athttp://www.analog-innovations.com| � �1962 � � | >> >> � � � � � � � � � �Spice is like a sports car... >> � � �Performance only as good as the person behind the wheel. > >Hi, > >I looked at your drawing and also simulated in pspice. Why did you go >for the High pass filter? I tried 220pF and 7.6KOhm. Is HPF more >accurate than LPF? > >The positive peak voltage is + 1 volts and negative peak voltage is - >1 volts. So, 2 volts peak to peak. > >I do not know how accurate should be the measured voltage. It would be >desirable to have it as little as possible. > >when said and done, I will read the voltage into the ADC and read the >numbers and try to monitor the voltage across the resistor. > >Thanks > >John One single point blank question: Is the ADC connected to a uC that you can program?
From: Jim Thompson on 2 Aug 2010 23:00
On Mon, 02 Aug 2010 19:36:20 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 30 Jul 2010 14:28:46 -0700 (PDT), john1987 ><conphiloso(a)hotmail.com> wrote: > >>On Jul 30, 5:16�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >>Web-Site.com> wrote: >>> On Fri, 30 Jul 2010 14:07:46 -0700 (PDT), john1987 >>> >>> <conphil...(a)hotmail.com> wrote: >>> >Hi, >>> >>> >200pF and 82 ohm resistor gives me approximately 9 Mhz frequency and >>> >its a high pass filter. SO, does it mean that filter will pass all the >>> >frequncies less than 9MHz. >>> >>> >Thanks >>> >John >>> >>> Stop snipping content and look at my drawing. >>> >>> � � � � � � � � � � � � � � � � � � � � ...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)460-2350begin_of_the_skype_highlighting��������������(480)460-2350������end_of_the_skype_highlighting�Fax: Available upon request | �Brass Rat �| >>> | E-mail Icon athttp://www.analog-innovations.com| � �1962 � � | >>> >>> � � � � � � � � � �Spice is like a sports car... >>> � � �Performance only as good as the person behind the wheel. >> >>Hi, >> >>I looked at your drawing and also simulated in pspice. Why did you go >>for the High pass filter? I tried 220pF and 7.6KOhm. Is HPF more >>accurate than LPF? >> >>The positive peak voltage is + 1 volts and negative peak voltage is - >>1 volts. So, 2 volts peak to peak. >> >>I do not know how accurate should be the measured voltage. It would be >>desirable to have it as little as possible. >> >>when said and done, I will read the voltage into the ADC and read the >>numbers and try to monitor the voltage across the resistor. >> >>Thanks >> >>John > >One single point blank question: Is the ADC connected to a uC that >you can program? Limited ability :-( ...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. |