Abstract: A crystal controlled square wave oscillator requiring a minimum number of components, exhibiting high frequency stability, and operating at substantially a 50% duty cycle. A quartz crystal dual monolithic resonator is provided having a pair of signal electrodes and a reference electrode. The resonator is capable of oscillating in symmetric and anti-symmetric modes, points of minimum attenuation, the symmetric mode exhibiting a 180.degree. phase shift, and the anti-symmetric mode exhibiting a phase shift of 0.degree.. An integrated circuit logic gate is connected between the signal electrodes, the logic gate being of the type having low input and output impedances so as not to degrade the Q of the resonator. The logic gate provides a phase shift of 180.degree. or 0.degree. causing the resonator to oscillate in its symmetric or anti-symmetric modes, respectively, the gate switching between its two logic levels to produce a square wave output at the frequency of the excited mode.

Abstract: A quartz crystal thermometer in which a standard frequency is generated by a first oscillator circuit incorporating a quartz crystal element and in which a frequency which varies with temperature is generated by a second circuit incorporating the same quartz crystal element. Two electrode pairs are provided on the single quartz crystal element in order to excite two different modes of vibration of the quartz crystal element, with the metallization being on only one or on both of the major faces of the quartz crystal element. In accordance with preferred embodiments, an AT- or a BT-cut quartz crystal plate is utilized. The ratio of the said two frequencies provides an accurate measure of the temperature.