EMRFD Message Archive 9511
Message Date From Subject 9511 2013-12-04 12:45:58 peepholenz Capacitance vs frequency Can someone give me an explanation of the physics behind the change in capacitance vs frequency as shown in the graph for X7R AVX ceramic caps...
See http://www.avx.com/docs/Catalogs/cx7r.pdf
Peter
9512 2013-12-04 13:01:37 Dana Myers Re: Capacitance vs frequency 9513 2013-12-04 13:36:56 Tayloe, Dan (NSN ... Re: Capacitance vs frequency The most alarming thing to me is that for these higher dielectric caps is that there is a significant change in C with the applied voltage. For audio circuits I would think a voltage dependant “C” would add distortion effects. Plus if you are using them in an R/C active filter, it would mess with the filter characteristics as well.
I notice the spec sheet does not go into the delta C vs. applied voltage.
- Dan, N7VE
9514 2013-12-04 13:44:44 peepholenz Re: Capacitance vs frequency Cap vs voltage - see http://www.johansondielectrics.com/images/stories/tech-notes/training/jdi_mlcc-basics_2007-12.pdf
Peter
ZL2AYX
9515 2013-12-04 13:45:06 Tayloe, Dan (NSN ... Re: Capacitance vs frequency At least the data sheet does say
“Capacitance for X7R varies under the influence of electrical operating
conditions such as voltage and frequency.”
Too bad they don’t show that voltage relationship.
- Dan, N7VE
9516 2013-12-04 13:52:00 Dana Myers Re: Capacitance vs frequency 9517 2013-12-04 13:54:25 Tayloe, Dan (NSN ... Re: Capacitance vs frequency I think that says if you try to use X7R in something more critical such as an audio active filter, try running at 10% or less of rated voltage. I.e., use a 50v part for a 5v application.
- Dan, N7VE
9518 2013-12-04 13:57:49 Graham / KE9H Re: Capacitance vs frequency
Not only are the High-K dielectric capacitors voltage dependent capacitors, they are also
piezoelectric. That is, audio vibrations can turn into voltage, and voltage variations
can convert into audio vibrations.
If you are designing a low noise amplifier circuit using them, you better make
sure the PC board is mounted in an acoustically-quiet environment. And not
be surprised when the PC board makes noises with high level signals going
through the amplifier.
--- Graham / KE9H
==
9519 2013-12-04 16:37:43 William Carver Re: Capacitance vs frequency
which breaks into oscillation at low temperature that would be someone
else's most alarming thing (I saw that happen in a product).
The product that developed oscillating regulators had a microcontroller
with many MB of fast static RAM, a DSP engine, microphone/speaker, and
battery to run it (intermittently) for months. It had to fit inside a 35
mm film can.
Size alone dominated their capacitor decision and they had a looming
disaster at the end of the project when they realized what the problem
was. Choice of capacitors should be a thoughtful one. Choosing one which
has dramatic changes in capacitance versus temperature, or capacitance
versus voltage better have a very compelling reason being that choice.
W7AAZ
On Wed, 2013-12-04 at 21:36 +0000, Tayloe, Dan (NSN - US/Tempe) wrote:
>
> The most alarming thing to me is that for these higher dielectric caps
> is that there is a significant change in C with the applied voltage.
> For audio circuits I would think a voltage dependant “C” would add
> distortion effects. Plus if you are using them in an R/C active
> filter, it would mess with the filter characteristics as well.
>
>
>
> I notice the spec sheet does not go into the delta C vs. applied
> voltage.
>
>
>
> - Dan, N7VE
>
>
>
>9520 2013-12-04 16:45:31 Russell Shaw Re: Capacitance vs frequency 9521 2013-12-04 16:58:00 Brooke Clarke Re: Capacitance vs frequency
When measuring capacitance of a device some equivalent circuit is used that typically has only capacitance and
resistance, but really many of these capacitors are made up of multiple layers.
The equivalent circuit may include some inductance.
http://en.wikipedia.org/wiki/Ceramic_capacitor#Series-equivalent_circuit
But when a simple 2 element equivalent circuit is used the apparent capacitance may show a frequency dependency that's
not really there when a better quality equivalent circuit is used.
The HP 4291 RF Impedance Analyzer is a swept frequency instrument that includes fitting a equivalent circuit that
includes inductance.
--
Have Fun,
Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html9522 2013-12-04 19:29:15 AD7ZU Re: Capacitance vs frequency 9523 2013-12-04 19:53:10 William Carver Re: Capacitance vs frequency
very high dielectric constant (lots of capacitance in small size) but
EVERYTHING was sacrificed: voltage, temperature and frequency all cause
the capacitance to change. And two caps will not necessarily change the
same amount. Matching just isn't in the cards.
Even immediately after the matching process, the match would disappear
immediately if the two caps were in a circuit with different voltages on
the two capacitors. If you matched them in the workshop at 55F and used
them in a warm radio that was 80F again they will drift differently with
temperature and not be matched any more.
At RF, with NPO ceramic, silvered mica, stacked (SMD) mica, or
polystyrene you could use an AADE very successfully. Hint: match them
with EXACTLY the same lead length (preferably zero, hi) because lead
inductance differences will look like capacitance differences at RF.
At audio/lower frequencies polypropylene, polystyrene or other stable
dielectric capacitors should stay matched.
All of those are stable dielectrics that have low sensitivity to DC
voltage and well-behaved temperature coefficients (either simply low, or
two examples matched at one temperature would both change the same
amount at a different temperature.
W7AAZ
On Wed, 2013-12-04 at 19:29 -0800, AD7ZU wrote:
>
>
>
> This discussion prompts me to wonder if selecting caps using something
> such as an AADE meter, or something far cruder in my case, would lead
> to errant selections when incorporated into a new circuit design.
> secondly: if matching caps for applications requiring more precision
> will selected caps behave consistently over a wide voltage range?
>
>
> Randy
> AD7ZU
>
>
>
>9534 2013-12-05 09:17:14 Andy Re: Capacitance vs frequency
It sure does.There are articles written about the subject of picking appropriate capacitor types for audio circuits. Occasionally I go back to one of the first that I remember, in "Audio" magazine that appeared somewhere in the 1970s. I think you can still download it from Walt Jung's website.Those same characteristics that can mess up audio circuits, can be pretty important to non-audio circuits too.73,Andy9537 2013-12-05 11:43:04 Dana Myers Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9538 2013-12-05 12:17:57 Brooke Clarke Re: Capacitance vs frequency
One other thing, is that they change value because of soldering into a circuit.
For example the 60 kHz loopstick antenna assemblies made by C-Max had a production problem because the individually
tested surface mount ceramic caps changed value when installed. They have since changed to capacitors with leads.
http://www.prc68.com/I/Loop.shtml#C-MAX
--
Have Fun,
Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html9539 2013-12-05 12:18:06 in3otd Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) That's interesting, I knew that board stress is important for precisi
9545 2013-12-07 10:01:45 Bill Higgs Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency)
9546 2013-12-07 11:18:50 n2msqrp Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency)
We replaced the LC filters with active filters using the 709 op amp. The gain-bandwidth product of the 709 was not high enough for the filters so the filter manufacturer had to supply hand selected op amps. I remember the replacement parts wer not cheap.
Mike N2MS
----- Original Message -----
9547 2013-12-09 09:26:31 Andy Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9548 2013-12-09 09:48:09 Dana Myers Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9549 2013-12-09 21:16:28 Russell Shaw Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9550 2013-12-09 22:57:36 Andy Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9551 2013-12-09 23:01:37 k6jq Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency) 9552 2013-12-10 06:11:35 William Carver Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency)
commercially for about three decades now (Endevco, etc).
W7AAZ
On Tue, 2013-12-10 at 01:56 -0500, Andy wrote:
>
> What part of the IC has the actual sensitivity (piezoelectric or
> strain)?
>
>
> Is it the silicon die, or the package or bondwires or their
> connections, I wonder?
>
>
> Regards,
> Andy
>
>
>
>
>9553 2013-12-10 08:44:56 Dana Myers Re: Audiophile op-amps (was Re: [emrfd] Capacitance vs frequency)