Design of fundamental mode suppressed AT-cut quartz resonator for nontuned third overtone oscillators
MetadataShow full item record
In striving for the elimination of mode selector or tuning circuit for the overtone operation of crystal controlled oscillators, a new resonator design having suppressed fundamental mode is presented in this thesis. The mode suppression was successfully achieved by restricting the electrode diameter to empirically established values and mass loading at crystal plate edge. Electrode diameter and electrode gap spacing are the two key parameters used to optimize the resonator performance. These surface perturbation effects, derived from the converse concept of trapped energy resonator and contouring at plate edge, significantly damp the fundamental mode vibratory energy and degrade the resonator Q. The resultant electrode arrangement was experimentally investigated and qualitatively discussed. For practical oscillator application, the preferred mode will be the one with lower motional resistance. Therefore, efforts have been made trying to obtain high fundamental mode motional resistance. This direct high frequency generation technique offers economical benefits such as component count and simplicity of circuit design. Resonators of such structure have been practically used in crystal clock oscillators.