[R-390] Ceramic Temp coefficients

[Bob Camp]

Hi

If you want to dig a bit deeper:

http://www.avx.com/docs/masterpubs/mccc.pdf

Yes, it's chip data, but the goop in a leaded part is the same stuff. Since chips have no leads, the series resonant data should be looked at as an upper limit.

--------------

Remember that we are talking about RF caps here. If there is audio involved, the decision process changes.

Bob

On Feb 11, 2013, at 6:43 AM, Sheldon Daitch <SDAITCH at bbg.gov> wrote:

> An interesting article on change over temperature characteristics of ceramic capacitors at:
> 
> 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
> 
> Enjoy,
> 
> 73
> Sheldon
> 
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Bob Camp
> Sent: Monday, February 11, 2013 5:15 AM
> To: r-390 at mailman.qth.net Group
> Subject: Re: [R-390] Ceramic Temp coefficients
> 
> Hi
> 
> There's a lot more to it than the simple EIA information. Ceramic caps (as previously mentioned) change capacitance with applied voltage. The X7R does this less than a Z5U. An NPO will beat any of the rest. They also have leakage (usually dimensioned in megohms per microfarad). Again, NPO wins the race compared to other ceramics. Next on the list is either microphonics (as in it's a ceramic mic) or dielectric absorption (as in short out the cap, come back in a while and there's voltage on it). NPO wins both of those as well, X7R comes in second.
> 
> So far that's all DC performance. In a radio IF, you likely have RF on the caps. Caps have both a Q and an effective series resistance. For most caps, the Q gets worse as frequency goes up past some magic point. Again NPO wins, X7R works pretty well at any R-390 type frequency. 
> 
> No, that's not the whole story. But it's already getting awfully repetitive. Simple answer is always - if it's ceramic use NPO if you can. If you can't get NPO, use X7R. If you can't use X7R, dig very deeply into what you are doing.
> 
> --------
> 
> That's just talking about ceramics. For DC performance, you can beat ceramics with *good* film caps in *good* packages. For purely RF specs, film caps generally are not going to perform as well as an NPO ceramic. 
> 
> Lots of choices. 
> 
> Bob
> 
> On Feb 10, 2013, at 7:55 PM, quartz55 <quartz55 at hughes.net> wrote:
> 
>> I've always been a bit confused about the TC on caps.  Here's a good 
>> one on the ceramics.  http://www.niccomp.com/Products/TC_Ceramics.pdf
>> 
>> N3DT
>