Forums

Ceramic capacitor value changes drastically with DC bias

Started by JW March 6, 2013
I don't think I've seen this discussed before - I did not know this.

http://www.edn.com/design/analog/4402049/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor
On 2013-03-06 14:55, JW wrote:
> I don't think I've seen this discussed before - I did not know this. > > http://www.edn.com/design/analog/4402049/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor >
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
On Mar 6, 8:55=A0am, JW <n...@dev.null> wrote:
> I don't think I've seen this discussed before - I did not know this. > > http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari...
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.
On Wed, 6 Mar 2013 06:37:06 -0800 (PST), George Herold <gherold@teachspin.com>
wrote:

>On Mar 6, 8:55&#2013266080;am, JW <n...@dev.null> wrote: >> I don't think I've seen this discussed before - I did not know this. >> >> http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari... > >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:

> 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.
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
On Mar 6, 10:20=A0am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Wed, 6 Mar 2013 06:37:06 -0800 (PST), George Herold <gher...@teachspin=
.com>
> wrote: > > >On Mar 6, 8:55=A0am, JW <n...@dev.null> wrote: > >> I don't think I've seen this discussed before - I did not know this. > > >>http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari..=
.
> > >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=
. 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.
> > -- > > John Larkin =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Highland Technology Incwww=
.highlandtechnology.com=A0 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 =A0analog, thermocouple, LVDT, synchro, tachometer > Multichannel arbitrary waveform generators
On Wed, 6 Mar 2013 07:58:27 -0800 (PST), George Herold <gherold@teachspin.com>
wrote:

>On Mar 6, 10:20&#2013266080;am, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 6 Mar 2013 06:37:06 -0800 (PST), George Herold <gher...@teachspin.com> >> wrote: >> >> >On Mar 6, 8:55&#2013266080;am, JW <n...@dev.null> wrote: >> >> I don't think I've seen this discussed before - I did not know this. >> >> >>http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari... >> >> >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. > >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.
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
On Wed, 06 Mar 2013 08:55:49 -0500, JW wrote:

> I don't think I've seen this discussed before - I did not know this. > > http://www.edn.com/design/analog/4402049/Temperature-and-voltage-
variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes- 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
On 03/06/2013 11:09 AM, John Larkin wrote:
> On Wed, 6 Mar 2013 07:58:27 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > >> On Mar 6, 10:20 am, John Larkin >> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> On Wed, 6 Mar 2013 06:37:06 -0800 (PST), George Herold >>> <gher...@teachspin.com> wrote: >>> >>>> On Mar 6, 8:55 am, JW <n...@dev.null> wrote: >>>>> I don't think I've seen this discussed before - I did not >>>>> know this. >>> >>>>> http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari... >>> >>>> >>>>>
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. >> >> 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. > > 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. >
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.
> 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. >
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
On Wed, 06 Mar 2013 11:31:04 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 03/06/2013 11:09 AM, John Larkin wrote: >> On Wed, 6 Mar 2013 07:58:27 -0800 (PST), George Herold >> <gherold@teachspin.com> wrote: >> >>> On Mar 6, 10:20 am, John Larkin >>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>> On Wed, 6 Mar 2013 06:37:06 -0800 (PST), George Herold >>>> <gher...@teachspin.com> wrote: >>>> >>>>> On Mar 6, 8:55 am, JW <n...@dev.null> wrote: >>>>>> I don't think I've seen this discussed before - I did not >>>>>> know this. >>>> >>>>>> http://www.edn.com/design/analog/4402049/Temperature-and-voltage-vari... >>>> >>>>> >>>>>> >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. >>> >>> 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. >> >> 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. >> > >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. > >> 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. >> > >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.
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