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Ceramic capacitor value changes drastically with DC bias

I built a little LNA (not wideband, ends ca. 50MHz IIRC) with 10uF 50V

1206 X7R caps coupling the input and output. Thought it was reading strange waveforms, maybe power supply transients or something, until I realized they were microphonic.

On further inspection, the transients observed from tapping the PCB have a frequency reasonable with respect to the acoustic length of said board.

FWIW, that was around 10mV for a casual finger tap. Think the caps were TDK. Soldered with big globs on either end, which will tend to increase strain.

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com
Reply to
Tim Williams
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Here in CA, when sudden weird jitters start to appear on a circuit like that, it's better to get the hell out of the building :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Years ago when I used to do some repairs for my buddies, I had one bring me a guitar amplifier. He could not use it because it was feed back, even when nothing plugged into it. He also noted when tapping on the cabinet, it was perfectly microphonic.

When I finally found the problem, it was a transistor in a plastic package. The package was fine and so was the transistor but something inside broke loose and was playing with the beta and made a perfect microphone.

I used that transistor in an FM oscillator and it worked perfectly as a bug!..

Jamie

Reply to
Jamie

u
a
e
e

Grin... well can you turn the lemon into lemonade? some sort of vibration sensor... upthread tm said to heat it above it Curie temperature.

George H.

Reply to
George Herold

Grin... well can you turn the lemon into lemonade? some sort of vibration sensor... upthread tm said to heat it above it Curie temperature.

George H.

+++++++++++++++++++++++++++++++

With a DC voltage applied. Allow it to cool with the DC applied and it should become very microphonic. Put an audio tone on it and you should hear it sing. Usually a soldering iron will get it hot enough but the material makes a difference.

Reply to
tm

t

e a

ar

Yeah I was going to ask what the curie temperature is? Is there a better 'flavor'?

Thanks, George H.

Reply to
George Herold 

--
Whoopie doo... 

This thread is about the change in ceramic capacitor capacitance 
values as a function of DC bias, so why on earth is your 
phototransistor circuit relevant?
Reply to
John Fields

It's all about "podium"... the inadequate need it perpetually renewed. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     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     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

AFAIK, barium titanate and related blends are in the 120C+ range, maybe

200C tops. Comparable to ferrites. They're definitely annealed in soldering, the chips at least.

If you have old discs that aren't measuring right, you can try soldering them, I suppose the mass and size of the disc may prevent the whole thing from heating up.

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

You're whining again. What do you have to say about capacitor dielectrics?

--

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
Reply to
John Larkin

And what do you have to say about capacitors?

Sad old fool.

--

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
Reply to
John Larkin

--- So, instead of admitting that your statement was self-serving and irrelevant, you dodge by pulling your one-trick pony out of the barn and have him whinny the "whine" word? How typically Larkinistic!

As for the dielectrics themselves, instead of wasting a lot of my time trying to reason with a hostile "client",

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and

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are good tutorials, with the latter illustrating the voltage coefficient of capacitance of the dielectric,

as does:

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from within

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However, the underlying cause of the parametric capacitance isn't gone into, and might be worth discussing if you can keep a civil tongue in your head.

Otherwise, f*ck off.

-- JF

Reply to
John Fields

So, when pushed into a corner, you can actually use google.

--

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
Reply to
John Larkin 

--
You don't really want to discuss electronics, then, you just want to 
bicker and make things unpleasant for the group.
Reply to
John Fields

Hey, *that* was funny. Not creative, but funny.

--

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
Reply to
John Larkin

You ought to know that Larkin _never_ puts forth anything that can be substantiated. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     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     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

What's actually going on here is that you have fallen so far behind the times, become so specialized, that you can understand only a small fraction of what's posted here. That's why you stay out of the more interesting threads, or only make lame posts about your Lexus and killing liberals and stuff.

Getting obsolete is a hazard of getting older. You've got to fight it.

--

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
Reply to
John Larkin

Piezo elements are too expensive I presume? :-)

--
Failure does not prove something is impossible, failure simply 
indicates you are not using the right tools... 
nico@nctdevpuntnl (punt=.) 
--------------------------------------------------------------
Reply to
Nico Coesel

I use them in a design for detecting pressing a 'button' through metal. If that isn't sub-Hertz... and the signal is pretty decent. Maybe they work better if you stick them on a medium (plastic) which can be warped a bit by the sound pressure.

--
Failure does not prove something is impossible, failure simply 
indicates you are not using the right tools... 
nico@nctdevpuntnl (punt=.) 
--------------------------------------------------------------
Reply to
Nico Coesel

Take apart one of those piezo butane lighters and get a whole stack of them.

Reply to
tm

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