Some non-electrolytic capacitor types such as polyester generate distortion when they have a significant signal voltage across them. This can be avoided by using polypropylene or polystyrene types but they are larger and more expensive. I have previously shown that in 2nd-order Sallen & Key filters, both lowpass and highpass, only one of the two capacitors has to be of the expensive sort to obtain the same freedom of distortion achieved with two. The Geffe configuration allows 3rd and 4th-order filters to be realized economically in one stage, and it is shown that here too only one linear capacitor is required in both lowpass and highpass cases, saving a lot of money.
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