Advanced Oscillator Technology Conquers Reference Degradation Due To Dynamic Environments

The Problem: The sophisticated military electronic systems aboard helicopters, missiles, and unmanned aerial vehicles (UAVs) must provide superior performance while being subjected to severe environmental conditions. The greatest impact on high performance comes from dynamic environments—those that induce degradations while the military platform is in motion accomplishing its intended mission. Of these mobile disturbances, vibration, acceleration, and shock have the greatest influence on performance. In light of this fact, a chasm exists between the performance of such systems in the quiescent (stationary) state versus while they are dynamic (mobile). The technology described herein closes this gap. It provides performance near theoretical quiescent limits while the platform is in the operational dynamic state.

The Solution: Sophisticated electronic systems have in common a precision frequency reference provided by a quartz-crystal oscillators—the heart of these systems—and the culprit of degradation in high dynamic environments. These internally mounted components generate the precision frequency and time signals that are crucial to system performance. Stress-compensated (SC)-cut quartz crystals have been extensively used as the resonating element in oscillator circuits. They are a reliable element for generating accurate frequencies.

Under static conditions (i.e., an acceleration-or vibration-free environment), a well-designed, SC-cut quartz-crystal oscillator will produce an output signal at a particular carrier frequency with relatively low sideband frequencies with respect to the carrier frequency. When the same oscillator is subjected to acceleration, however, undesirable spurious sidebands occur in the output signal. When motion and vibration are encountered, these spurious sidebands and unwanted signal noise can translate into overall system errors—depending on the particular oscillator application. In essence, acceleration forces, vibration, and shocks cause the oscillator's stability and accuracy performance to degrade and in turn degrade the system performance. The "g" (acceleration)-compensated quartz oscillator technology makes significant in-roads toward defeating such dynamic degradations.

The Technology: The FEI g-compensation technology has already been deployed in a host of systems. It promises to provide performance improvements for critical military platforms in high dynamic environments. The technology is based on a breakthrough in two main areas:

1. New methods of stress-compensated quartz resonator design and manufacturing, which provide for minimum cross-coupling between the three axes. Because each axis is more independent of the other, compensation is more effective. Each specially produced quartz resonator with low crosstalk and low g-sensitivity will have a resultant three-axes response (see figure). That response, which is defined as Gamma (g), is minimized for each application.
2. New sensing devices that can more easily be matched and mounted to each resonator axis

As linear and oscillator accelerations are applied, the low cross-coupled resonator responds and so do the sensing devices. The sensors generate compensation signals and in concert with the compensation electronics adjusts the amplitudes and phase relationships of the signals, which results in cancellation effects. These effects compensate for the oscillator's g-sensitivity while achieving the significant improvements shown in the figure.

Frequency Electronics, Inc., 55 Charles Lindbergh Blvd., Mitchel Field, NY 11553; (516) 794-4500,

Internet: www.freqelec.com.