QUARTZ VIBRATOR PARAMETER DETERMINATION BY PARALLEL BRIDGE METHODS.

Bridge methods are the most accurate means of determining the parameters of quartz vibrators, particularly in the VHF region, and above. Present and future crystal requirement specifications point toward the increasing use of such methods to obtain the accuracy necessary for both filter and oscillator applications. A practical difficulty which arises is that the ranges of any given bridge are not compatible with every immittance characteristic encountered with the various crystal types in use, particularly if measurements are to be made over substantially different portions of the region of resonance. One means of obviating this difficulty is to augment the crystal with another impedance element in series or parallel so that the behavior of the combination is accommodated within the bridge ranges; the value of the augmenting element is determined separately, usually on the same bridge. Thus a capacitance in parallel with the crystal is suitable for reducing the impedance variation when using impedance bridges which consider the unknown as a series combination of resistance and reactance, while a series element reduces the admittance variation in parallel bridges--those representing the unknown as a conductance and susceptance in parallel. It is one purpose of this technical report to discuss the applicability and limitations of this latter procedure, and describe how the crystal parameters are extracted from measurements of this type. (Author)