On 2023-02-21 15:54, John Larkin wrote:> 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.> To do optical measurement to that sort of precision, what do you use > for the light source?One of two models of LED source, based on either a 7-ns LED ($2) or a 2-ns LED ($50). For simple stuff I usually hang a LED barefoot on a Highland P400 DDG, then dork the pulse height to get the right brightness. Our LED source boxes are coming out Real Soon Now, with a BNC, a wall wart, mounting flanges, laser-inscribed case, perspulex running boards, ion drive, et cetera et cetera. ;) Inside, they're a 74AC14 driving one of the magic fast LEDs, with an AP2205 adjustable LDO providing a stable VDD. Subnanosecond edges, lots of drive, cheap like borscht. That way we get everything out of the LEDs. The AP2205 is a nice part--an adjustable small LDO with 36V max input, 2% accuracy, and _built-in polarity protection_, all for 15 cents. I may switch my allegiance from the venerable LP2951.> > Here's my photodiode calibrator for the ill-fated LAM project. > > https://www.dropbox.com/sh/0gsjeh8m94a0nbs/AAC_uLD7aO5QF6Qat6dR2NoFa?dl=0Nice pastel green color! 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 21, 20232023-02-21
Reply by ●February 26, 20232023-02-26
On Monday, February 20, 2023 at 5:02:53 PM UTC-8, Clifford Heath wrote:> On 21/02/23 11:36, legg wrote: > > On Mon, 20 Feb 2023 15:03:09 -0500, Phil Hobbs > >> 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,Back in the 1970s we had several hundreds 10% 1K TH carbon resistors. I measured a couple hundreds and crudely plotted the bins (years before "spreadsheet" software was all the rage.) Sure enough, the distribution had peaks at roughly +- 10%, and steps at ~5%. Just as everyone had been saying since the ?1950s? So, buy a too-high value, and then discard all the +5% capacitors, to create a single gaussian peak? Heh! OOoo! Build a highspeed machine which rapidly measures a whole spool, then mechanically extracts all the off-value components. Then next, SELL THE MACHINES. (For a much higher price, also offer the machine which re-spools SMT components, where the originating spool has many positions unfilled. Hmmm, maybe such products already exist?)
Reply by ●February 28, 20232023-02-28
On 2023-02-21, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> The AP2205 is a nice part--an adjustable small LDO with 36V max input, > 2% accuracy, and _built-in polarity protection_, all for 15 cents. I > may switch my allegiance from the venerable LP2951.That looks like a nice part (the adjustable startup time might be useful), but I don't see anything about reverse polarity protection in the datasheet, only reverse current protection. There is a new product announcement for the part which touts reverse battery protection, but the datsheet is lacking such information. cu Michael -- Some people have no respect of age unless it is bottled.
Reply by ●February 28, 20232023-02-28
On 2023-02-28 09:59, Michael Schwingen wrote:> On 2023-02-21, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >> The AP2205 is a nice part--an adjustable small LDO with 36V max input, >> 2% accuracy, and _built-in polarity protection_, all for 15 cents. I >> may switch my allegiance from the venerable LP2951. > > That looks like a nice part (the adjustable startup time might be useful), > but I don't see anything about reverse polarity protection in the datasheet, > only reverse current protection. > > There is a new product announcement for the part which touts reverse battery > protection, but the datsheet is lacking such information. > > cu > Michael >Yeah, I see that. I don't have any more info either--when they come in I'll try it out. 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
