CRYSTAL FILTERS

• US 3,599,124 A
• Filed: 04/24/1968
• Issued: 08/10/1971
• Est. Priority Date: 04/24/1968
• Status: Expired due to Term

• Current Assignee: Roger A. Sykes, Warren L. Smith
• Original Assignee: Roger A. Sykes, Warren L. Smith
• Inventors: Smith, Warren L., Sykes, Roger A.
• Application Number:
  US04/723,677
• Time in Patent Office: 1,203 Days
• US Class Current: 333/32
• CPC Class Codes: H03H 9/566 Electric coupling means therefor H03H9/0095 takes precedence

Abstract

Three or more resonator-forming electrode pairs and a crystal wafer on which they are mounted, form a multiresonator crystal filter with respective inductors connected to two of the pairs. The electrode pairs have masses such as to tune the frequency exhibited by the unconnected resonator to a frequency fp. The inductors tune the interelectrode capacitances of the connected resonators to the frequency fp. The masses of electrodes in the connected resonators tune the mechanical resonance of the crystal between the electrodes to the frequency fp. The electrode spacings in view of their masses are such as to achieve predetermined couplings between resonators.

Claims

1. An electromechanical filter comprising, in combination, a body of piezoelectric material, input electrode means sandwiching a first region of said body therebetween, output electrode means sandwiching a second region of said body therebetween, means for applying electrical energy to said input electrode means, means for extracting electrical energy from said output means, intermediate electrode means sandwiching said body therebetween located between said input and output electrode means, each of said electrode means having sufficient mass to decrease exponentially the amplitude of acoustic energy in said body as the distance from said electrode means increases, thereby to confine said acoustic energy substantially to a limited acoustic field in said body close to said electrode means and away from the edges of said body, each of said electrode means being spaced at a preselected distance within the acoustic field of each adjacent one of said electrode means, the portions of said body between each adjacent pair of said electrode means being coupled acoustically as a result of the combined effect of said mass and said distance whereby energy transfer between said pairs is limited substantially to acoustic energy, inductor means connected to said input and output electrode means, thereby to facilitate accurate shaping of the passband characteristics of said filter, said intermediate electrode means comprising a single pair of short-circuited electrodes, said inductor means forming a respective tuning circuit with each of said input and output electrode means, and each of said tuning circuits being tuned to the mechanical resonant frequency of a respective one of the resonators formed by said input and output means.

2. An electromechanical filter comprising, in combination, a body of piezoelectric material, input electrode means sandwiching a first region of said body therebetween, output electrode means sandwiching a second region of said body therebetween, means for applying electrical energy to said input electrode means, means for extracting electrical energy from said output means, intermediate electrode means sandwiching said body therebetween located between said input and output electrode means, each of said electrode means having sufficient mass to decrease exponentially the amplitude of acoustic energy in said body as the distance from said electrode means increases, thereby to confine said acoustic energy substantially to a limited acoustic field in said body close to said electrode means and away from the edges of said body, each of said electrode means being spaced at a preselected distance within the acoustic field of each adjacent one of said electrode means, the portions of said body between each adjacent pair of said electrode means being coupled acoustically as a result of the combined effect of said mass and said distance whereby energy transfer between said pairs is limited substantially to acoustic energy, inductor means connected to said input and outpuT electrode means, thereby to facilitate accurate shaping of the passband characteristics of said filter, said intermediate electrode means comprising a plurality of pairs of electrodes, said inductor means forming a respective tuning circuit with each of said input and output electrode means, and each of said tuning circuits being tuned to the mechanical resonant frequency of a respective one of the resonators formed by said input and output means.