[sdiy] Hand-matching capacitors for filter stages

[Dave Manley]

Neil Johnson wrote:
>
> Basic ceramic caps (at the cheaper end, e.g. Y5V) are highly 
> voltage-dependent - the capacitance decreases with applied voltage.  
> The effect in a filter at various amplitudes is left as an exercise 
> for the reader, but do check out the AVX datasheets for Y5V ceramics 
> and see how much the capacitance changes over a 0-10V range.
>
There's an old design example in EDN (or similar) for a VCO where the 
frequency was set by changing the voltage across a Y5V (or Z5U?) 
capacitor.  It was an interesting curiosity that directly showed this 
effect.  Of course, this is done all the time in production oscillators 
where the capacitor is replaced by a varactor.

-Dave