Wireless Systems Design

Oscillators Keep Projectiles On Target

The requirements for military applications are obviously more severe than consumer demands. Yet these technologies still must provide the latest services and enhancements. As an example, the new temperature-compensated crystal oscillators (TCXOs) from C-MAC Micro-Technology merge high stability with acceleration resistance and small size.

This group of devices is prepared for harsh environments. The CFPT-9025 range is designed to withstand acceleration up to 20,000g. Typical applications for the TCXOs include guided missiles, guided mortar shells, and other smart munitions that add GPS satellite guidance to conventional projectiles.

In the development of missile-guidance systems, a lot of emphasis is placed on the time taken to acquire the GPS signal after the shock of launch. The reference oscillator that determines this elapsed time has three key requirements: small physical size; a low shock-induced frequency offset following launch; and low deviation from nominal frequency. This last requirement must be met in spite of possibly extreme temperature—and while the missile is in the barrel of the launcher, shielded from the incoming reference signal.

The CFPT-9025 is packaged as a ceramic SMD measuring just 9.22 × 7.57 × 3mm. Its stability specification of ±1.0 ppm (with respect to nominal frequency) has been tested following exposure up to 20,000g acceleration. The temperature stability of ±1 ppm over ±55° to +95°C is achieved using Pluto, the company's proprietary analog temperature-compensation ASIC. Shock resistance is imparted by use of a special g-hardened crystal resonator and solid construction.

For missile-guidance applications, the CFPT-9025 has a standard nominal frequency between 10 and 50 MHz. The frequency adjustment range is ±5.0 ppm. The device operates from a 3.3-V supply. It provides a clipped sinewave output.

The CFPT-9025 range also includes specifications for use in handheld GPS receivers. These offer even higher stability of ±0.5 ppm over a less demanding military temperature range of −40° to +70°C. They carry a lower shock-resistance specification as well.

C-MAC MicroTechnology
4222 Emperor Blvd., Suite 300, Durham, NC 27703-8466; (919) 474-3500, FAX: (919) 941-0530, www.cmac.com/mt/.

TAGS: Components
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