I don't think I've seen this discussed before - I did not know this.
- posted
11 years ago
I don't think I've seen this discussed before - I did not know this.
Yeah, I got acquainted with that particular problem in the 1980's. High-K ceramics have all sorts of non-ideal behaviour. Capacitance varies with temperature and bias voltage, they are piezo-electric, hysteretic and tend to crack. If they couldn't be made so tiny, no one would want to use them.
There was one thing in your link that *did* surprise me: One commenter claims to have used a batch of caps that would oscillate all by themselves at 900 MHz when biased. I won't believe that until I see it.
Jeroen Belleman
It's been talked about in passing here, where the idea of using a Z5U (or Y) as part of a low frequency VCO.. (Hey Joerg how 'bout a cermaic cap for you 10kHz VCO?)
George H.
You could make a parametric amplifier with them. Power gain would be huge.
-- 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
Jeroen Belleman schrieb:
Hello,
a parametric oscillator? If I would see it, I would try to remove all semiconductors from that board to see if it still oscillates.
Bye
. .
Scratch, scratch... (google google)... OK I'm not sure how a parametric amplifer works. I 'did' a parametric oscillator in the past, but even that is a bit vague now. (I recall a plot of drive amplitude versus frequency that looked like a semi-circle, with a threshold.)
Got a link (or pic) that might explain it? (It's a mixer type thing, no?)
George H.
.highlandtechnology.com jlarkin at highlandtechnology dot com
Run high-frequency AC through a cap, and then rectify and drive a load. Vary the DC bias on the cap to change the power transferred into the load.
Parametric amps and oscillators used to be popular for RF stuff, using PN varicap diodes, but regular semis got faster and the paramps faded away.
-- 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
a-0-33--F-capacitor
It's been discussed. It's a known issue with high dielectric constant ceramics, and part of the reason that you want to avoid them unless you really need the capacitance in the space you can provide.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
It's been talked about in passing here, where the idea of using a Z5U
That's sort of a mag amp/saturable reactor approach, which would be easy to do.
A real paramp (one with pump, idler, and signal resonances) might be kind of hard to build, since Y5V caps below about 4.7 nF have basically disappeared, even in the really small sizes. I still have a few hundred
2200 pF ones that I bought to try this, but haven't got round to it yet. I suppose you could build a really low-Z one, e.g. 4.7 nF and 10 uH, to work around 1 MHz or thereabouts.I've never actually built one, but I've always wanted an excuse. I wonder how much gain you could get out of an 0201 capacitor?
Actually, one pretty cool application would be a floating isolation amp. A paramp doesn't necessarily need DC bias, so you can power it just from the RF pump.
Cheers
Phil Hobbs
-- 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 hobbs at electrooptical dot net http://electrooptical.net
There were potted-brick parametric opamps that had pretty good specs, Philbrick maybe. The floating front end differential stage was a pair of varicaps pumped at a MHz or so, all transformer coupled. I recall that TI (?) even did an IC opamp with a varicap front-end.
Nonlinear ceramic caps have been used to make shock lines, to speed up the leading edges of pulses. They work in the kilovolt range. I have a paper on that, somewhere.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
I have used the effect for moving a filter around. It doesn't get any cheaper than that.
Right now I am looking for capacitors with the worst microphonics because I want to use them ... as contact sound sensors. But has to be low enough in capacitance so I can reasonably squeeze 100Hz bandwidth out of them.
-- Regards, Joerg http://www.analogconsultants.com/
Also, don't automatically assume that X7R is always golden and never has that problem. The very high density ones often do and it can be very tough to pry some data about that out of manufacturers. BTDT, a lot. Murata is pretty good when it comes to furnishing such data so they are currently my preferred source.
-- Regards, Joerg http://www.analogconsultants.com/
Delta-c over C should be independent of C, so if you charge a cap through a big resistor, and look at the voltage, bandwidth should be OK for a big cap.
I did a little testing about ceramic caps generating noise from tapping the board and didn't see anything. We lost phase lock when a front-panel SMB connector was pulled out... turned out to be the XO. We had some tiny springs fabricated to shock isolate the dip14 oscillator.
How about a cheap piezo chirper disk?
I once designed a circuit that crashed a product if the cover was removed, using a phototransistor to detect light. I never used it.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
If you take a ceramic capacitor and apply the rated DC voltage across it and heat to above the curie point, when it cools it will exhibit the piezo effect.
With MLCC one never knows. All kinds of weird effects.
When I got the Fluke 8845A, or rather after UPS (literally!) threw it over the backyard fence, I took an older ceramic cap and hooked it up to it. Turned it to AC, all 6-/12 digits of it. Every time I clapped my hands near that cap I could see the excursion.
This meter is nice, no fan. But the relays clicking around when in ohms-mode are a bit annoying.
They are not very good at very low frequencies, sub-Hertz and such.
Or design one where it quits working for a minute every time someone says "s..t!" :-)
-- Regards, Joerg http://www.analogconsultants.com/
I wonder what the feedback sounds like with that.
Like this: Dang!
For customers in the south: Daiang! :-)
-- Regards, Joerg http://www.analogconsultants.com/
High capacity surface-mount ceramics also make good microphones when they've got a lot of bias on them. They're great blocking caps if you have a low-level signal riding on a lot of DC that you want to corrupt with ambient vibration.
-- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
I have an 8845A, replacing the horrible Chinese rebrand Keithley I sent back. Great meter, the Fluke.
The relay click is a good audible continuity indicator!
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Ah, that's what it's for :-)
It is a great meter but one thing I'll never understand: It's not the slowest on the continuity beep but if I drag the probe across a set of traces too fast it misses. The cheapo Chinese meter doesn't! So for continuity tests I'll keep using one of the Chinese meters. I wish the large companies would talk to their clients some more.
I'll still have to try out LAN and PC operation. It shipped with a little USB-RS232 gizmo. For the LAN I'll wait for warmer weather because it's a crawl space job to get Ethernet there. It came with some sort of Fluke software but (as usual with many US companise ...) that seems to only be some teaser kit.
-- Regards, Joerg http://www.analogconsultants.com/
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