| AndrewT |
Hi all,
what is the difference between NPO and COG ceramic capacitors?
How might it affect their intended end use? |
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| mzzj |
| quote: | Originally posted by AndrewT
Hi all,
what is the difference between NPO and COG ceramic capacitors?
How might it affect their intended end use? |
Nada, they are same thing. And its NP0 and C0G, not NPO or COG
"Negative-Positive-Zero" as tempco is +-30ppm :) |
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| AndrewT |
Thanks Mzzj,
What is C0G? |
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| jacco vermeulen |
| COG is the name of the dielectric type. |
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| serengetiplains |
| C0G capacitors have excellent dielectric characteristics which compete with better film varieties: low distortion, low DA, low DF. X5R capacitors, and its siblings, are another matter entirely having dielectric characteristics that compete with the worst of electrolytics for Worst Capacitor Ever. |
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| serengetiplains |
Seeing as I mentioned the dreaded X5R, here's a distortion plot of an X7R. Says Cyril Bateman who performed the test generating the plot:
"This 10nF X7R ceramic was made by a CECC approved, European manufacturer. It was tested at 1kHz and 3 volts, in series with a 10k ohm current limiting resistor. Measurable distortion exists at all voltages down to 0.5 volts – my lowest test voltage." |
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| serengetiplains |
| Here's the same test on a C0G. |
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| RetroAudio |
| I've been using NPO/COG caps in a variety of places with extremely good results,..at least to the ear. |
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| AndrewT |
Hi Serenq,
that's some difference -63db (x7r) reduced to -127db for the C0G.
Thanks to all.
Is the low distortion an indication that ppm/V is not an issue for C0G and NP0 when used in Audio locations. We all use ceramic in bypass duty. |
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| infinia |
Hi Tom,
Thanks for the plots. Do you have the test configuration diagram?
Too bad ceramics a got a bad rap in the audio world. They are really good performers if used properly. But can a nightmare if misused. (piezo microphonics). I still use em X7R included and could not be without.
Generally use for low imp/supply bypass. Never in high imp/ high gain circuits like feedback networks. NP0's abound in RF world up to several GHz. |
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| serengetiplains |
| Infinia, here's Bateman's test jig. Sorry for the resolution; it's as good as I could make it. |
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| infinia |
Yikes that'll break my eyeballs. Way too much detail. Couldn't even find the DUT. Would it be possible to draw something highly simplified? do it have DC bias with resistor impedance? AC generator levels/imp @1KHz, spectrum analzer used, etc
Alternatively if it's really a bother links on the web for tests like these that are handy. sorry this is interesting for me. |
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| mzzj |
| quote: | Originally posted by infinia
Alternatively if it's really a bother links on the web for tests like these that are handy. sorry this is interesting for me. |
See if you can get "Electronics World" at your hands in library or whatever, C. Bateman had something like 12-part article spread over one year issues about capacitor distortion and its causes.
You can do sub-ppm distortion measurements relatively easily with ultra-low distortion oscillator, passive notch filter and mid-level PC soundcard equipped with FFT software. But first you need super-quality caps wich are polypropylene extended metal foil (not metallized film) |
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| forr |
Cyril Bateman used to sell a CD-rom full of his articles on caps (and many more). Send me an email and I'll send him your contact, I think he'll then contact you. Sorry for the procedure, but he had huge problems with his spammed email box and it is preferable to make contacts with him a bit complex.
For his sub-1ppm distortion test I built, I am looking for a freeware handy spectrum analyser using a PC-sound card. Any idea ? |
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| mzzj |
| quote: | Originally posted by forr
For his sub-1ppm distortion test I built, I am looking for a freeware handy spectrum analyser using a PC-sound card. Any idea ? |
28euros for Audiotester is not that bad. |
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| AndrewT |
Hi,
now I've got it.
C 0 G is the EIA three character code for -0 +-30 ppm/Cdeg.
and this happens to be N P zero (NP0).
Thanks all.
Any response to cap variation with voltage for this type? ppm/V? |
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| mzzj |
| quote: | Originally posted by AndrewT
Any response to cap variation with voltage for this type? ppm/V? [/B] |
Very low as distorition measurements show. |
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| infinia |
Mzzj,Forr,
Thank you for your kind suggestions. I will check my puplic/uni library for the WW publications when I go. I think it is important for the test diagram/conditions to be included with plots/test data when the information is to be analyzed correctly.
Praxis v2.14 in time domain has been used by others on this forum. FYI All PC SpAnalyzers use FFT in function.
For PC SA see the following link I found.
http://www3.ocn.ne.jp/~hanbei/eng-winanalyzer.html |
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| jcx |
RMAA -RightMark Audio Analyzer is popular, not very flexible
Audacity project at Sourceforge will help you grab/create/edit .wavs
Scilab (just checked, Scilab.org website is down over this weekend) has wav import and I think I've seen a useful looking analysis package in thier reference page - free matlab work alike has many of the heavy duty matlab toolboxes for signal analysis
Cyril's circuitry isn't the best for the application - considerable simplification can be had with indirect nonlinearity measurements of IM differences - no need to build a low distortion oscillator, better recent 24 bit sound cards can also add ~ 20 dB resolution vs his setup - esi juli@, emu 1212m are < us$200 |
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| pooge |
Whether or not Bateman's test setup is the best or not, all of the caps tested were tested on that common denominator, and valuable comparisons could be made.
The NP0/C0G caps looked really good in all aspects. They were at the top of the heap in just about everything. They practically appear to be the perfect cap.
However, he did not test microphonics. Whether or not this is a real issue, I have not been able to determine. Because Class 1 caps do not use barium titinate, a piezoelectric material, they are orders of magnitude better than Class 2 ceramics that do, which should not be used for such critical applications such as a feedback compensation cap. The best info I could find about microphonics wrt Class 1 caps is that microphonics are "low". However, while all caps have some degree of microphonics, determining the relative value of Class 1 ceramics vs. caps other than Class 2 ceramics has not been easy to find. If the microphonics of Class 1 is less than, say, silver mica, they could be a perfect low cost, easily available cap for those critical applications such as feedback compensation, etc. |
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| infinia |
| quote: | Originally posted by pooge
Whether or not Bateman's test setup is the best or not, all of the caps tested were tested on that common denominator, and valuable comparisons could be made.
it's OK no biggie I just wanted a look see
The NP0/C0G caps looked really good in all aspects. They were at the top of the heap in just about everything. They practically appear to be the perfect cap.
I agree. Practical values (limit case size) are a little small for audio
However, he did not test microphonics. Whether or not this is a real issue, I have not been able to determine. Because Class 1 caps do not use barium titinate, a piezoelectric material, they are orders of magnitude better than Class 2 ceramics that do, which should not be used for such critical applications such as a feedback compensation cap. The best info I could find about microphonics wrt Class 1 caps is that microphonics are "low". However, while all caps have some degree of microphonics, determining the relative value of Class 1 ceramics vs. caps other than Class 2 ceramics has not been easy to find. If the microphonics of Class 1 is less than, say, silver mica, they could be a perfect low cost, easily available cap for those critical applications such as feedback compensation, etc. |
Believe me microphonics are there and are very real. There are in direct proportion to the amounts of Barium T used in the caps. I was involved with a corp in developing a demodulation IC for TV settop boxes. And the analog tuner ahead of our chip was giving us high BitError rates in proto testing. Along story short the tuner's LO PLL had an X7R cap in feed back of loop filter integrator. You could tap with your finger on the bench and count the errors.
Had the tuner vendor change to film cap there you go all fixed.
My belief is harmonic distortion and microphonics are related to piezo mechanics of Barium T parts. Test crystal's with same set up. |
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| serengetiplains |
| Infinia, send me a pm. |
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| jcx |
np0/c0g are very good but not quite perfect:
I have seen ~ -110 dB 2nd order difference in an amp with 2x series 100V np0 caps in a sallen-key 40 KHz low pass with 20 + 21 KHz 1:1 @ 8V pk sine drive
after replacing the np0 with polystyrene the 1 Khz diff dropped below my~ -160 dB measurement limt ( ~ -130 dB noise floor in a Lynx22 sound card + 30 dB gain @ 1 KHz) |
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| serengetiplains |
Hi jcx, Bateman's tests show that polyproplenes beat NP0s, and styrenes beat propylenes. Teflons are currently at the top of the heap for distortion, DA, etc.
Note that Bateman's test setup is not ideal for testing the better capacitors---though it does give some relative indication---as the measuring instrument he designed uses less than the best capacitors in all parts of the circuit. |
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| RetroAudio |
| it's been shown before that all the dielectrics and the cap construction play a part in this performance,..and that they vary from cap to cap,..you just have to test them. some npo's can outperform other pp and ps caps,..just depends. not all pp caps are alike. |
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| forr |
Thanks for your help concerning FFT software.
JCX
---Cyril's circuitry isn't the best for the application - considerable simplification can be had with indirect nonlinearity measurements of IM differences---
Cyril is currently doing experiments with TDFD tests, a kind of IM measurements whose idea comes from Neville Thiele (1975) : almost unknown (at least to me till a few weeks ago), its sensitivity to non-lineraity can beat THD. |
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| pooge |
| quote: | Originally posted by infinia
Believe me microphonics are there and are very real. There are in direct proportion to the amounts of Barium T used in the caps. I was involved with a corp in developing a demodulation IC for TV settop boxes. And the analog tuner ahead of our chip was giving us high BitError rates in proto testing. Along story short the tuner's LO PLL had an X7R cap in feed back of loop filter integrator. You could tap with your finger on the bench and count the errors.
Had the tuner vendor change to film cap there you go all fixed.
My belief is harmonic distortion and microphonics are related to piezo mechanics of Barium T parts. Test crystal's with same set up. |
Class 1 ceramics (NP0/C0G) do not use barium T. X7R caps are class 2. |
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| serengetiplains |
| Forr, any chance Cyril might update us on his project? I really appreciate what he's done in measuring capacitor distortions---one of the few guys with proper credentials and experience to pull something like that off. |
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| davidsrsb |
There seems to be some confusion between microphonics and piezo in this thread.
Even an ideal parallel plate capacitor with vacuum dielectric would be microphonic if the plate gap can be modulated. This only happens if there is a dc bias. Piezo voltage is generated by stress so it happens even with no dc bias or gap modulation.
Microphonics by gap modulation will depend on the capacitor construction, pcb thickness and pcb support |
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