MONOLITHIC CRYSTAL FILTER

摘要

A monolithic crystal filter includes a monolithic crystal filter element, a capacitive network connected in series with the monolithic crystal filter element and a bridging capacitor connected across the monolithic crystal element and the capacitive network. The monolithic crystal filter provides a passband that is symmetrically located about the passband center frequency. The monolithic crystal filter element has two pairs of electrodes that resonate at substantially the same frequency. The resonating frequencies of the electrode pairs are preferably below the passband center frequency. The capacitive circuit raises the resonating frequency of one of the electrode pairs such that the geometric mean of the raised and non-raised electrode-pair frequencies is substantially the same as the passband center frequency. The monolithic crystal filter can be cascaded with one or more similar monolithic crystal filters or monolithic crystal filter elements to obtain greater selectivity.