| Electronics > Projects, Designs, and Technical Stuff |
| Non microphonic, 1uF SMT cap in a high Z circuit? |
| (1/5) > >> |
| dmills:
So I have a dc removal servo integrator (1M ohm, 1uF caps), and I am after building this thing SMT, question is, what to use for the integrator cap? I need something non microphonic (critical, which rules out class II dielectrics) and low leakage, and I don't know which polarity will be applied. Current thinking is PPS film from Wima or Kemet, but I am seeking the brain trusts input on this one. I would rather avoid reaching for banks of 10 of the (Awesome) 100nF C0G parts that are now available on cost and space grounds if nothing else. The other downside of these is that they are not generally available as soft term parts and in 1206 that is not a good thing. |
| Conrad Hoffman:
Not sure but PPS is probably OK. Is there any way to raise the impedance further, say 10X and use a smaller cap? |
| dmills:
10 Meg is getting annoying from a offset current perspective even with the excellent chopper opamps now available, also getting into a space where board cleaning is becoming critical..... I could, but I would very much rather not as a gut reaction, might be worth some spice modelling tonight to see what I get however, as 100n I use elsewhere on the board in C0G. Regards, Dan. |
| Conrad Hoffman:
I think dielectric absorption is the thing to look at, and it's also the thing with the least data available. >:( |
| DaJMasta:
Two back to back 2uF tantalums? Even if you don't know the polarity, can you bias it in a way that whatever the eventual signal is, you have a set polarity, and you can just use a small electrolytic or tantalum? While there are plenty of film caps and stuff that would fit the bill, I think the ones small enough to be smaller than the proposed array of C0G caps probably are pretty pricey (though maybe not in comparison of 1uF worth of C0G caps). Would stacking the C0Gs be viable/give you the footprint you were looking for? |
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