Detecting the peak value

I don't need to go that fast :)

But there's a spot where I need a very slow ramp. Think around mV per minute or slower type ramps.

Probably a dithery DAC (delta-sigma), since drift over hours may kill a current source into cap multiplier for such a slow ramp rate.

Though years ago I did work with an amazing circuit that implemented a three hour timer by making 1uF look like 10000uF, add 68M resistor, and feed a 555! Was in a very noisy environment where CMOS counters simply failed.

Used a super gain preamp in front of opamp for the cap multiplier, metal can opamps.

Grant.

And the top end of PICs are in that range also.

Yeah, it's scary. I'll stay with the 12F & 16F for now, thanks.

Grant.

+/- 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.

What I had in mind...

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.

^^^--- your

Yes you do... accuracy of test current. (Or chopper-stabilized.)

(Or chopper-stabilized.)

...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.

Voice:(480)460-2350begin_of_the_skype_highlighting              (480)460-2350      end_of_the_skype_highlighting Fax: Available upon request |  Brass Rat  |

One single point blank question: Is the ADC connected to a uC that you can program?

Voice:(480)460-2350begin_of_the_skype_highlighting              (480)460-2350      end_of_the_skype_highlighting Fax: Available upon request |  Brass Rat  |

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.

Actually it sounds kind of like a varaition of a Phantastron.

That is a real issue with better and best grade caps, i would be more worried about the measurement problems created by dielectrics with serious voltage non-linearities like Z5U.

To the extent you can get HP user and service manuals for their (low frequency ~ 10 Hz to ~ 10 MHz) LCR meters / impedance analysers. They mostly used semibridge techniques with I&Q demodulators. Of serious interest if the methods used to measure capacitors (including with voltage bias) and inductors (including with current bias).

And that don't ring a bell, you having a lend of me? :)

One day I'll put these .pdfs into some mind-mapping thingy so I can find the stuff again. Sometimes I'll spend hours going through circuits for ideas, concepts. App notes, data sheets, and so on. But the recall is a bit scrambled these days, too much information.

Grant.

Voice:(480)460-2350begin_of_the_skype_highlighting              (480)460-2350      end_of_the_skype_highlighting Fax: Available upon request |  Brass Rat  |

I am partly trying to discover the constraints to partitioning the system. Like using a 10 MSPs converter and digitally peak detecting outside a uC. Or can we just find the peaks, several workable alternatives have been proposed, and digitize them as they occur. OP also asks about what ADC to use. Way too much how come for why actual contsraints are missing.

Many of us would help OP but do not like running up blind alleys sans exit.

Why ?:-)

Can a Z5U stay within even 1% for a few seconds when left alone? ...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.

...

That's the crazy cap that traps charge so 'well' you got to heat them up to release it?

Grant.

Cause i thought it would be clearer to OP in this case (without buggering up things with pros too much).

Too many, too easy to find with a search. And too many could be clearer than mine. IIRC is agressively used some imperfections in pentodes to fight / semi-cancel other imperfections.

Not when you put a voltage ramp to it. OPs measurement method. It goes very squirrely by 20% of rated voltage. Time required to get outside 1% is sub-microsecond. I would not trust them to stay within

1% on any paramater for one millisecond in real use. Doesn't mean they can't be useful.