Nope. Ceramic capacitors are rated at room temperature and at zero bias. All ceramic material has a lousy V/C curve, some much worse than others. C0G is bad enough but as JL has pointed out Y5V or such can lose 2/3s, or even more, of the rated capacitance at rated voltage. This is something board designers always have to take into account and why ceramic caps are really good at distorting audio.
Irrelevant. It's the materials. The rated capacitance is *only* at zero bias (kinda useless). The C/V curve isn't specified, except as nominal.
Don't pretend there isn't with chips.
If you're paying for it, it's available. It's one thing that the automotive specs do but it doesn't come free.
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058
hobbs at electrooptical dot net
http://electrooptical.net
Actually, C0G is better than any film*, in tempco and ESR, and maintains rated tolerance at many times rated voltage. That's part of why they're expensive.
Only type II (high K) dielectrics suck.
*At least, films that you can get. Teflon might be better, but far more expensive. If you can even find them.
--you can control it electronically, using a PLL or FLL. I agree that they aren't the most stable things in the world, but neither are silicon varac tors. So what? It's inside a feedback loop. Of course, one has to maint ain enough design margin to guard against eventualities, but that's SOP.
John's particular problem. It is, however, one very cheap, simple, and pr obably effective solution. I didn't invent it, but I think it's pretty.
It's got its charms, but John particular problem rests in his delusion that he can't get an inductor better than +/-20%, and that trimmable inductors have to be small and high frequency.
Several people have pointed out that this is wrong - including me, Jim Thom pson and Phil Allison, none of whom he likes very much, so he's ignored the point.
Just to waste a bit more bandwidth repeating the information, he could buy a heavily gapped ferrite core which could offer - say - 160nH+/-3% per turn squared - and wind himself a +/-3% inductor. If he bought a heavily gapped EPCOS P26x16 pot core with a central hole, he could also buy a screw-in ad juster which offers fine control of inductance by bridging the central gap in a smoothly variable way.
It's a very old-fashioned solution, but it works really well, and has done so for years. The parts are still stocked by some broad line distributors, including Newark and Farnell. I've posted part numbers in this thread.
One of my more hilarious moments was when I was invited into a Top Secret meeting with an Admiral... who proceeded to describe his needs with a MULTI-block diagram on a chalk board (~1965 :)
After about 1/2 hour of this, I jumped up and accurately guessed what he was actually trying to do... much to his consternation that I had guessed his "secret".
I then proceeded to show how to do it with about 5% of the number of blocks.
Ever since I have always allocated enough time in my quotations to have a complete "shakedown cruise" with the customer to determine his actual needs. Makes for much smaller and much less expensive chips... that yield good!
Most of the time I get to do it my way. Occasionally I'll get an insistent customer, then I make sure they sign-off on their way of doing it. They usually end up being sorry for being insistent. (They're usually PhD's >:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
We check a few parts on every reel, in receiving, before we put them into stock. When we saw those 2.2uF caps being almost all out of tolerance low, we used several different c-meters; all read about the same.
Maybe some other guys could check their hi-K caps.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
The "L" has no other function than to just sit there and recirculate current? No further use than amusement ?>:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
And designating you a smug, useless smart-ass. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I don't use them. I think I use one X6S and everything else is either C0G(small stuff) or X7R. X7R is bad enough at voltage. I don't need worse problems. I've found that high-K caps aren't worth the money spent on them.
I once designed some FPGA-based video cameras (color and a FLIR) for a military application. The frame and bit rates were classified (secret) but the number of lines and pixels per line (COTS CCDs and FPAs) and horizontal rate weren't, so I had to work with that "incomplete" information because I didn't have a clearance (and didn't want one). ;-)
The government really is as screwed up as Obamacare. Everywhere.
The best metalized polypropylene capacitors have ESRs and DA at least as good as the best C0Gs (for C>=1nF or so), maybe even better. Sorry, they're not cheap either, but possibly a better choice if C*V >? 5 V*uF.
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