A New Generation of Very High Stability BVA Oscillators

Abstract

A third generation of "Oscilloquartz" OCXO's using the technique of housing a BVA SC-cut crystal resonator and its associated oscillator components in double oven technology has been developed with the funding support of European Space Operations Centre (E.S.O.C). The main purpose is to provide a local oscillator for high performances ground clock [ref 1].The main features targeted of that new "8607-C series" are to get significant improvements compared to the classical "state of the art" 8607-B design in a better short term stability @ 1 sec in Allan variance, a better-low phase noise and outstanding short term stability and a better-high isolation from "pressure and humidity" variations.

Volume dependence in handel's model of quartz crystal resonator noise

“…Since the comparison of the previous graphs clearly shows that one should not forget that the quality factor depends on the physical dimensions of the resonator, we study in more details the thickness dependence of ⁄ . For that purpose, we recall that, in the expression Since, for the same specific kind of resonator that was used for the record measurement [5], the motional capacitance was measured to be 0.195 fF in [3], we have together with (7) of the main text, a set of two nonlinear equations in and R. In order to solve them numerically, we compute initial estimates of and R using first the fact that the thickness at the center of the resonator 2 is approximately given by 2 3/2. In the present case, since the acoustic velocity for the 5 MHz thickness shear C-mode in a SC-cut quartz crystal is ̂ ⁄ 3613 m/s ( = 2650 kg/m 3 ), we find that 2 1.084 mm Then, we use the fact that the electrodes diameter is always chosen big enough so that the two Gaussian integrals in …”

“…with Q the intrinsic quality factor of the resonator, V (in cm 3 ) the volume of the resonant part inside the resonator, and  a proportionality factor dependent on the physical parameters of the material, numerically estimated to be of the order of 1 cm 3 in quartz resonators. We note first that this is supposed to represent the fundamental lower limit of noise spectral density at low frequencies, in the resonator, therefore in the oscillator.…”

“…This seemed to be the ultimate limit that one could obtain for a quartz based oscillator in the short-term stability domain since, no more tangible solution had been found to improve the phase noise of the resonator itself. Recently, better experimental results [3][4][5] have reintroduced hopes that quartz crystal oscillators may still have a progression margin in the short-term stability domain and refueled the discussion about what is the main factor limiting the stability between the phase flicker noise in the electronics and the intrinsic noise of the quartz crystal.…”

“…So far, ultra-stable oscillators (USO) using quartz crystal resonators remain the best solution to have the highest short-term stability in volumes of a few cm 3 which is very important for local time references in space applications (for example) since size and weight are important parameters. With low noise electronics at the state of the art, the fundamental limitation for this short-term stability is flicker frequency noise in the resonator (hereafter simply called 1/f noise).…”

Optically referenced broadband electronic synthesizer with 15 digits of resolution

“…Although research into varied photonic and electronic schemes have strived to improve upon the spectral purity of microwave and millimeter-wave signals, the reliance on conventional electronic synthesis for tuning has resulted in limited progress in broadband sources. Using a digital-photonic synthesizer architecture that derives its time-base from a highstability optical reference cavity, we generate frequency-agile and wideband microwave signals with exceptional dynamic range and with a fractional frequency instability of 1 × 10 −15 at 1 s. The presented architecture demonstrates digitally controlled, user defined and broadband frequency tuning from RF to 100 GHz with orders-of-magnitude improvement in noise performance over room-temperature electronic wide-bandwidth synthesis schemes.0.01-10 s comes from oven-controlled 5 MHz quartz with a stability as good as 8 × 10 −14 [9]. Further improvements in the stability of electronic oscillators on this timescale have required operation at cryogenic temperatures, with impressive achievements in Q and stability coming from quartz, niobium and sapphire dielectric resonators in the microwave X-band [10][11][12][13].…”