Reducing phase noise degradation due to mechanical vibration on high performance quartz resonator oscillators for gateway applications

Abstract

Many modern telecommunication systems rely on a common signal source to serve as a phase and frequency reference signal for the network. This source is often employed to synthesize microwave transmit and receive signals locally for gateway signal processing purposes and to serve as a reference for the remotely located signal sources in the network. This scheme has the advantage of providing end-to-end network synchronization and reducing the cost of the remote terminals by requiring a high-performance phase and frequency source only at the gateway site.Achieving extremely low-phase noise for this common reference source in order to meet the performance demands over microwave radio links is the challenge. The high phase noise multiplication factor associated with this process drives the phase noise performance of the reference source to be state of the art.Electronic equipment for gateway telecommunications facilities is typically fashioned using a modular chassis-in-rack concept. This concept provides ease of maintainability and design configurability through an industry-standardized rack and chassis mounting system. In some applications, the racks are located on elevated flooring in order to facilitate inter-rack connectivity and site thermal management. This physical approach to gateway site facilities, while succeeding in providing a useful realization of the aforementioned design needs, does not provide a vibration-free environment for sensitive phase and frequency signal sources. The source of the vibration energy, due to mechanical influences, is notably from site air movement equipment, localized rack cooling blowers, staff operations (walking, closing of doors, etc.), physical building movement, etc.A design solution for this gateway application that employs a g compensated quartz crystal oscillator as a signal source is presented. This signal source is mounted on a vibration isolation device to effectively remove the residual mechanical vibration disturbances affecting phase noise. The oscillator utilizes a Stress Compensated (SC) cut quartz resonator with optimized circuit design and g compensation functionality to achieve state-of-the-art phase noise performance. The vibration isolation device features an entirely passive implementation and excellent mechanical isolation capabilities at a reasonable cost. The resultant phase noise performance under operational vibration conditions is nearly equivalent to the quiescent, at-rest, performance. The composite g sensitivity is better than 1 X 10 -11 /g at 5 Hz offset for this system application.

Emerging applications requiring precision time and frequency

“…FEI has developed a microprocessorcontrolled precise frequency generating system comprised of a rubidium oscillator phased locked to a low gsensitivity quartz oscillator. The main characteristics of the system consist of: Emerging applications for g-compensated, stable frequency sources are in Earth Stations as explained by Ernst, et al [12].…”