Hi, all, We're making some 7-pole active lowpass filter boards, primarily to go into test systems (ours and other people's). It would be convenient to be able to use 0.5% resistors and 5% capacitors. There are 2% caps available in most of the range we want, but they're expensive and relatively scarce. If we could get a few reels of 5% caps, we could dork the resistor values to get the right frequency response, _provided_ that the parts on the reel cluster closer than 5% in value. Have any of you folks done any measurements on the consistency of NP0 cap values within a reel? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Capacitors on reels--any tendency for values to cluster?
Started by ●February 20, 2023
Reply by ●February 20, 20232023-02-20
On Monday, February 20, 2023 at 3:03:24 PM UTC-5, Phil Hobbs wrote:> Hi, all, > > We're making some 7-pole active lowpass filter boards, primarily to go > into test systems (ours and other people's). > > It would be convenient to be able to use 0.5% resistors and 5% > capacitors. There are 2% caps available in most of the range we want, > but they're expensive and relatively scarce. If we could get a few > reels of 5% caps, we could dork the resistor values to get the right > frequency response, _provided_ that the parts on the reel cluster closer > than 5% in value. > > Have any of you folks done any measurements on the consistency of NP0 > cap values within a reel?If they are EIA standard capacitors then they should all be within 0.5% of nominal. They do this so the capacitance is within the spec'd error band for rated value under all conditions of rated stress it's spec'd for. Of course I may just be making this up, because I know it to be a certainty for resistors and only assume there's a similar requirement for capacitors.> > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC / Hobbs ElectroOptics > Optics, Electro-optics, Photonics, Analog Electronics > Briarcliff Manor NY 10510 > > http://electrooptical.net > http://hobbs-eo.com
Reply by ●February 20, 20232023-02-20
On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Hi, all, > >We're making some 7-pole active lowpass filter boards, primarily to go >into test systems (ours and other people's). > >It would be convenient to be able to use 0.5% resistors and 5% >capacitors. There are 2% caps available in most of the range we want, >but they're expensive and relatively scarce. If we could get a few >reels of 5% caps, we could dork the resistor values to get the right >frequency response, _provided_ that the parts on the reel cluster closer >than 5% in value. > >Have any of you folks done any measurements on the consistency of NP0 >cap values within a reel? > >Cheers > >Phil HobbsThe parts are bulk (funneled) before test and taping. Don't buy 5% from anyone offering 2% and expect a normal distribution. RL
Reply by ●February 20, 20232023-02-20
On 21/02/23 11:36, legg wrote:> On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Hi, all, >> >> We're making some 7-pole active lowpass filter boards, primarily to go >> into test systems (ours and other people's). >> >> It would be convenient to be able to use 0.5% resistors and 5% >> capacitors. There are 2% caps available in most of the range we want, >> but they're expensive and relatively scarce. If we could get a few >> reels of 5% caps, we could dork the resistor values to get the right >> frequency response, _provided_ that the parts on the reel cluster closer >> than 5% in value. >> >> Have any of you folks done any measurements on the consistency of NP0 >> cap values within a reel? >> >> Cheers >> >> Phil Hobbs > > The parts are bulk (funneled) before test and taping. > > Don't buy 5% from anyone offering 2% and expect a > normal distribution.Interesting. Lemme guess: a bimodal distribution? -5..-2, +2..+5? Clifford Heath.
Reply by ●February 21, 20232023-02-21
On 21/02/2023 01:02, Clifford Heath wrote:> On 21/02/23 11:36, legg wrote: >> On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Hi, all, >>> >>> We're making some 7-pole active lowpass filter boards, primarily to go >>> into test systems (ours and other people's). >>> >>> It would be convenient to be able to use 0.5% resistors and 5% >>> capacitors. There are 2% caps available in most of the range we want, >>> but they're expensive and relatively scarce. If we could get a few >>> reels of 5% caps, we could dork the resistor values to get the right >>> frequency response, _provided_ that the parts on the reel cluster closer >>> than 5% in value. >>> >>> Have any of you folks done any measurements on the consistency of NP0 >>> cap values within a reel? >>> >>> Cheers >>> >>> Phil Hobbs >> >> The parts are bulk (funneled) before test and taping. >> >> Don't buy 5% from anyone offering 2% and expect a >> normal distribution. > > Interesting. Lemme guess: a bimodal distribution? -5..-2, +2..+5? > > Clifford Heath. >Or all 2%. -- Cheers Clive
Reply by ●February 21, 20232023-02-21
On 21/02/2023 7:03 am, Phil Hobbs wrote:> Hi, all, > > We're making some 7-pole active lowpass filter boards, primarily to go > into test systems (ours and other people's). > > It would be convenient to be able to use 0.5% resistors and 5% > capacitors. There are 2% caps available in most of the range we want, > but they're expensive and relatively scarce. If we could get a few > reels of 5% caps, we could dork the resistor values to get the right > frequency response, _provided_ that the parts on the reel cluster closer > than 5% in value. > > Have any of you folks done any measurements on the consistency of NP0 > cap values within a reel? > > Cheers > > Phil Hobbs >Do you put these boards through some sort of test jig in production? If so, could you make it electronically adjust the resistors at test and store the settings in EEPROM? You wouldn't need a proper digital pot, just a few steps of coarse adjustment (with some analog switches or even tristated microcontroller pins) to get from 5% to 2%, though it would be tempting to make it much better. For low volumes you could do one of those schemes where an operator cuts off a resistor on some units. You can get capacitor arrays with NP0 dielectric - I wonder whether the matching within each unit is better than between separate ordinary MLCCs - though the datasheet doesn't say and it wouldn't solve your problem anyway.
Reply by ●February 21, 20232023-02-21
On 2023-02-21 04:57, Clive Arthur wrote:> On 21/02/2023 01:02, Clifford Heath wrote: >> On 21/02/23 11:36, legg wrote: >>> On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> Hi, all, >>>> >>>> We're making some 7-pole active lowpass filter boards, primarily to go >>>> into test systems (ours and other people's). >>>> >>>> It would be convenient to be able to use 0.5% resistors and 5% >>>> capacitors. There are 2% caps available in most of the range we want, >>>> but they're expensive and relatively scarce. If we could get a few >>>> reels of 5% caps, we could dork the resistor values to get the right >>>> frequency response, _provided_ that the parts on the reel cluster >>>> closer >>>> than 5% in value. >>>> >>>> Have any of you folks done any measurements on the consistency of NP0 >>>> cap values within a reel? >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> The parts are bulk (funneled) before test and taping. >>> >>> Don't buy 5% from anyone offering 2% and expect a >>> normal distribution. >> >> Interesting. Lemme guess: a bimodal distribution? -5..-2, +2..+5? >> >> Clifford Heath. >> > > Or all 2%. >I'd expect that to be more likely. You can't afford much test time for a part that sells for a fraction of a cent. I'll have to get a few reels and see, I suppose. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●February 21, 20232023-02-21
On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Hi, all, > >We're making some 7-pole active lowpass filter boards, primarily to go >into test systems (ours and other people's).Sharp cutoff? That's going to be tricky at 7 poles. I like passive LC filters when feasible; they are less twitchy. Might you make your filter trimmable somehow? That could be fun. Pity that switched-cap filters are/were so awful. Seems like someone could make a thinfilm all-analog programmable filter, but I guess it's not worth the trouble. The monolithic ceramic filters are all up at outrageous frequencies, not suited for DDS filtering or most of the real-world signals we work with. All the effort is going into narrowband wireless where the money is.> >It would be convenient to be able to use 0.5% resistors and 5% >capacitors. There are 2% caps available in most of the range we want, >but they're expensive and relatively scarce. If we could get a few >reels of 5% caps, we could dork the resistor values to get the right >frequency response, _provided_ that the parts on the reel cluster closer >than 5% in value. > >Have any of you folks done any measurements on the consistency of NP0 >cap values within a reel? > >Cheers > >Phil HobbsYou could assign one of your lab lackeys to measure some caps here and there on a reel or two, and report back here. We did order a reel of truly custom-brewed caps from Capax, 3.3 pF N4700, to temperature compensate our instant-start LC oscillators. That worked great. Maybe they would make you a reel of close-matched parts.
Reply by ●February 21, 20232023-02-21
On 2023-02-21 11:33, John Larkin wrote:> On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Hi, all, >> >> We're making some 7-pole active lowpass filter boards, primarily to go >> into test systems (ours and other people's). > > Sharp cutoff? That's going to be tricky at 7 poles. I like passive LC > filters when feasible; they are less twitchy. Might you make your > filter trimmable somehow? That could be fun. > > Pity that switched-cap filters are/were so awful. Seems like someone > could make a thinfilm all-analog programmable filter, but I guess it's > not worth the trouble. The monolithic ceramic filters are all up at > outrageous frequencies, not suited for DDS filtering or most of the > real-world signals we work with. All the effort is going into > narrowband wireless where the money is. > > >> >> It would be convenient to be able to use 0.5% resistors and 5% >> capacitors. There are 2% caps available in most of the range we want, >> but they're expensive and relatively scarce. If we could get a few >> reels of 5% caps, we could dork the resistor values to get the right >> frequency response, _provided_ that the parts on the reel cluster closer >> than 5% in value. >> >> Have any of you folks done any measurements on the consistency of NP0 >> cap values within a reel? >> >> Cheers >> >> Phil Hobbs > > You could assign one of your lab lackeys to measure some caps here and > there on a reel or two, and report back here. > > We did order a reel of truly custom-brewed caps from Capax, 3.3 pF > N4700, to temperature compensate our instant-start LC oscillators. > That worked great. Maybe they would make you a reel of close-matched > parts. > > >Turns out that in the hundreds of picofarads we can get 1% caps for reasonably cheap. The filters are 12-dB transition Gaussians, made with LT1260 triple CFAs and a THS4631 output stage. I want really blameless performance--less than 0.5% overshoot, 1% bandwidth accuracy, 4:1 shape factor, ideally < 10 nV noise, good linearity. The amps all have 1 kV/us slew rates, which helps a lot when you have no control over what ugly thing somebody's going to connect to it. The idea is to be able to characterize photoreceivers for noise using a true-RMS meter rather than a scope FFT or spectrum analyzer, and to have a choice of bandwidths. Simon is doing a nice box with four of them: 10 kHz, 100 kHz, 1 MHz, 5 MHz. We really don't want to do any tweaking if we can possibly help it. Going to 10 MHz or higher would probably need LCs, at least for the higher-Q sections. The current design is three Sallen-Key sections with equal or nearly equal resistors, and one RC pole on the first stage. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●February 21, 20232023-02-21
On Tue, 21 Feb 2023 14:40:51 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2023-02-21 11:33, John Larkin wrote: >> On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Hi, all, >>> >>> We're making some 7-pole active lowpass filter boards, primarily to go >>> into test systems (ours and other people's). >> >> Sharp cutoff? That's going to be tricky at 7 poles. I like passive LC >> filters when feasible; they are less twitchy. Might you make your >> filter trimmable somehow? That could be fun. >> >> Pity that switched-cap filters are/were so awful. Seems like someone >> could make a thinfilm all-analog programmable filter, but I guess it's >> not worth the trouble. The monolithic ceramic filters are all up at >> outrageous frequencies, not suited for DDS filtering or most of the >> real-world signals we work with. All the effort is going into >> narrowband wireless where the money is. >> >> >>> >>> It would be convenient to be able to use 0.5% resistors and 5% >>> capacitors. There are 2% caps available in most of the range we want, >>> but they're expensive and relatively scarce. If we could get a few >>> reels of 5% caps, we could dork the resistor values to get the right >>> frequency response, _provided_ that the parts on the reel cluster closer >>> than 5% in value. >>> >>> Have any of you folks done any measurements on the consistency of NP0 >>> cap values within a reel? >>> >>> Cheers >>> >>> Phil Hobbs >> >> You could assign one of your lab lackeys to measure some caps here and >> there on a reel or two, and report back here. >> >> We did order a reel of truly custom-brewed caps from Capax, 3.3 pF >> N4700, to temperature compensate our instant-start LC oscillators. >> That worked great. Maybe they would make you a reel of close-matched >> parts. >> >> >> > >Turns out that in the hundreds of picofarads we can get 1% caps for >reasonably cheap. > >The filters are 12-dB transition Gaussians, made with LT1260 triple CFAs >and a THS4631 output stage. I want really blameless performance--less >than 0.5% overshoot, 1% bandwidth accuracy, 4:1 shape factor, ideally < >10 nV noise, good linearity. > >The amps all have 1 kV/us slew rates, which helps a lot when you have no >control over what ugly thing somebody's going to connect to it. > >The idea is to be able to characterize photoreceivers for noise using a >true-RMS meter rather than a scope FFT or spectrum analyzer, and to have >a choice of bandwidths. > >Simon is doing a nice box with four of them: 10 kHz, 100 kHz, 1 MHz, 5 MHz. > >We really don't want to do any tweaking if we can possibly help it. >Going to 10 MHz or higher would probably need LCs, at least for the >higher-Q sections. The current design is three Sallen-Key sections with >equal or nearly equal resistors, and one RC pole on the first stage. > >Cheers > >Phil HobbsTo do optical measurement to that sort of precision, what do you use for the light source? Here's my photodiode calibrator for the ill-fated LAM project. https://www.dropbox.com/sh/0gsjeh8m94a0nbs/AAC_uLD7aO5QF6Qat6dR2NoFa?dl=0
