NPO ceramic vs polypropylene

Ha ha, should have looked it up. So there is no escape. (I think my brain was mixing it up with COG as in chip-on-glass LCDs).

Yes, I got confused between different dielectric types and which was the best for the application. Well, now that NP0 ceramic are available in the needed value and voltage, and at a reasonable cost, there's no point in messing with film anymore! But, there are a LOT of units out there with the film caps that seem to still be working fine.

Jon

Hi guys,

Spehro Pefhany Inscribed thus:

How do glass capacitors fare in relation ? Thanks:

Interesting.. I think they're better again, I've not used them. Perhaps better than anything else with a reasonable epsilon.

AVX shows them up to 2400pF.

See the DA curve on the 3rd-last page.

Judging by all the radiation and MIL spec stuff they don't look very inexpensive.

--sp

I had always avoided ceramics in S&H circuits due to bad DA memory effects.

If you have high reactive current, plastic is far superior to ceramic for high Q, insensitivity to DC bias, loss tangent, tan Delta vs f, piezo sensitivity.

For low current LC tuning in RF , NP0 or P250 was my preference using TDK or Murata.

You can now get quite high value NP0 caps.. not cheap at the highest values, but 0.1uF/50V for 37 cents in 100's isn't too terrible for a all that capacitance squeezed into a 1206 (and 10x better tempco than a PP cap).

--sp

Hi Spehro,

Spehro Pefhany Inscribed thus:

Thanks for the link.

The reason I asked is that I have a lot of "Dow Corning" glass capacitors of various values and have not been able to find any info about them. Some are quite high capacitance values and close tolerance ie 1%.

I was just looking at .22uF C0Gs at DigiKey. They're not small (1210s are the smallest) and NOT cheap ($1.34 ea. if you buy a whole reel

-2000 pcs.). Murata doesn't seem to have anything that big.

Trying to figure out the cost of external components for a chip design can be tricky since the volume purchase prices are not published. But when you do the arm twisting and find the numbers, the pricing of small ceramic capacitors requires 4 to 5 significant figures if evaluated as a unit price.

For sample and hold applications, dielectric absorption is the key parameter.

Oh...as in gears...

Maters not,it is STILL a gear...

Maybe two 0.1 uF in parallel?

George H.

Mine? Not particularly but eight 1210s would blow the space given

If there's vertical room you could piggy back 'em. But I guess not practical for a large number of units. Maybe wait a few years and ceramics will keep getting better? A 1uF (50V) NP0 for a buck or two would be nice.

George h.

Not very production friendly, either. A buck or two???? Yikes! Pennys hurt.

The trick of using two in series and biasing the middle will reduce the distortion there too.

Cheers

Phil Hobbs

You may be missing the point if tuned circuits are actually the topic.

Polystyrene tempcos are expected to cancel out those of ferrite. An NPO or other film dielectric couldn't do that, unless paralleled with a nother part with a suitable tempco. Caps aren't the weak point in this area. RL

That's an interesting idea, however it costs some seriously quiet references and only helps 3dB.

Well, in a single-supply circuit, you can probably bias the midpoint at ground. And the even-order distortion should cancel quite a bit better than 3 dB, unless the caps are +-100% tolerance.

Cheers

Phil Hobbs