Method of fine-tuning a monolithic crystal filter

摘要

A method of fine-tuning a monolithic crystal filter (11) having a solid electrode (16) on one side of a crystal wafer (13) and a pair of split electrodes (12-1 and 12-2) on an opposite side of the wafer, to define a pair of resonators (19 and 21), involves short-circuiting one of the split electrodes to the solid electrode to produce a filter resonator coupling frequency wave form having first and second peaks (P. sub.A and P. sub.B), the positions of which correspond to upper and lower short circuit resonator resonant frequencies (F.sub.A and F.sub.B), respectively, of the filter. Additional electrode material then is plated on one or the other half of the solid electrode (16) to balance the wave form peaks (P.sub.A and P.sub.B), thus balancing the open circuit resonator resonant frequencies of the filter (11). Additional electrode material then is plated on the entire solid electrode to fine-tune the midband frequency (F.sub.M) of the filter (11) to a final desired value (F.sub. MF).