bypass-capacitorcapacitordecoupling-capacitorpcb-design
For my pcb which will be used at very low temperatures, say 50 K, I am searching appropriate Bypass Caps. Many papers stated that NP0(C0G) Caps are especially good because of their constant temperature behaviour.
But now the problem is that I need a 10 uF Bypass, which does not exist with NP0 dielectricum.. What alternatives do I have?
Till now I have a 1 nF (size 0603), 10 nF (0603), 100 nF (1203) all NP0 Ceramics.
Appreciate any help
Many thanks
An ideal capacitor has an impedance that falls with increasing frequency, which is good for decoupling high-frequency noise.
However, real capacitors have some amount of parasitic inductance, which appears in series with the capacitance, forming a series-resonant circuit.
Such a circuit has a minimum impedance at its resonant frequency, and at frequencies higher than that, the impedance starts rising again, which is less useful for decoupling.
That's why it's sometimes useful to use a number of different capacitors to decouple wide-bandwidth applications; each one provides the low impedance required for a particular band of frequencies.
But beware of strange cross-resonant effects! Sometimes the capacitance of one capacitor will interact with the inductance of another capacitor to create a parallel-resonant circuit, which has a very high impdeance at its resonant frequency. Verify your implementation with a wide-band network analyzer.
Your question is naive in that it doesn't consider what type of capacitor best suits the target application. Consider this: -
So, a 1uF ceramic may not be your best choice if wanting an accurate timing circuit (for instance) or some audio application where the microphonic problems associated with a ceramic capacitor cannot be tolerated. Also, these days, it's quite normal to find ceramics up at 100 uF and I'm sure in a few years time 1000 uF will be possible.
What do you suggest?
Choose a capacitor type that suits the application. If one doesn't exist look at alternatives and if those alternatives look problematic, find a different approach.
Pretty picture taken from here.
Best Answer
Looks like solid tantalum can be suitable for larger values at cryogenic temperatures, on the following nasa study the "in situ" column is when the part is still at liquid nitrogen temperatures.
Nasa Study