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

When a frequency is applied to a crystal filter, the piezoelectric properties of the quartz crystal cause it to vibrate at its resonant frequency. The filter selectively allows frequencies within its passband to pass with minimal loss while attenuating out-of-band frequencies. This high selectivity ... read more