A crystal filter is classified as a passive device because it operates without external power, relying solely on the piezoelectric properties of quartz crystals and passive components (capacitors, inductors). Unlike active filters, it cannot amplify signals—only filter specific frequencies through m... read more

An OCXO (Oven-Controlled Crystal Oscillator) is classified as an active component because it requires external power to function. Unlike passive components, an OCXO actively generates and stabilizes frequency signals using internal oscillator circuits and a temperature-controlled heating element ("o... read more