Resonators are used in various different circuits and integrated circuits (chips). Resonators can have a plurality of different resonant frequencies. Resonators include electrical circuits such as LC circuits which include an inductor and a capacitor. Some resonators include an array of capacitors, or more generally impedances, which are tuned by selectively switching capacitors in the array. Resonators are used to generate signals having a particular desired frequency. Filters may also use switched impedances to generate a desired narrowband passband function.