analysis of noise origin in ultra stable resonators: Preliminary Results on Measurement bench

The Centre National d'Etudes Spatiales (CNES), Toulouse, France and FEMTO-ST Institute, Besancon, France, have initiated a program of investigations on the origins of noise in bulk acoustic wave resonators. Several European manufacturers of high quality resonators and oscillators take part in this operation. Tests and measurements are mainly performed on an advanced phase noise measurement system, recently set up for this program. The bench principle uses carrier suppression technique. The carrier signal of the driving source is split into two equal parts to drive both crystal resonator pairs. Noise of both resonators is measured through symmetrical ways in order to suppress the source noise. Investigations on the sensitivity of selected quartz crystal resonators to various externally-controlled parameters such as temperature, drive level, load impedance, and series capacitance are presented. Various batches of different types of 5 and 10 MHz quartz crystal resonators provided by the industrial partners have already been tested (conventional, QAS, BVA, ...). Results are discussed with a special attention on some specific topics. The influence of the temperature is particularly studied according to the operating point versus the quartz crystal turn over temperature. A double enclosure and two thermally controlled ovens are used in order to control the quartz crystal temperature. The temperature step can be lower than 0.05°C between two remote-controlled operating temperatures around 80 °C. Measurements are compared to a review of theoretical aspect of temperature effects in quartz crystal resonators. In the measurement system, the resonator frequency of each arm of the bench has always to be tuned, as in an oscillator. This is fulfilled by a series capacitor having a pull-up effect. Several sets of measurements have been compared. Resonator noise is observed according to the input power in the bench arm. The frequency tuning is achieved with the series capacitor or with the source frequency. Resonator noise is also measured at constant resonator power according to a wide range of series capacitors. The tuning capacitor modifies the overall impedance, thus, correlation between load impedance and the flicker noise of the resonator is analyzed through the previous measurements. Finaly, a discussion about the contributions of the different parameters to the measurement results is done