FreeLists / si-list / [SI-LIST] Re: Antwort: Re: Placement of Decoupling Caps

[John Barnes <jrbarnes@xxxxxxxxx>]

Paul,
NPO is an old acronym for "negative positive zero", for ceramic
capacitors that have a nearly-constant dielectric constant (K, also
known as permittivity).  The temperature coefficient for the capacitance
is approximately 0 parts-per-million per degree C over the specified
operating temperature range for the capacitor. 

If you are designing a critical inductor-capacitor (LC) tuned-circuit,
you may want to compensate for the (usually) positive temperature
coefficient of the inductor.  By parallelling two ceramic capacitors,
one with a specified negative temperature coefficient, and one with an
NPO/C0G temperature coefficient, you can vary the ratio of their values
to get just about any nominal value and negative temperature coefficient
that you may need.  Doug DeMaw's ham-radio books talk about this scheme
in a lot more detail.
                                        John Barnes  KS4GL
                                        dBi Corporation
                                        http://www.dbicorporation.com/
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