Anderson Electronics, Inc. - Tutorial (DRAT)

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DRAT - Doubly Rotated AT Cut Crystals
DRAT is an acronym for Doubly Rotated AT. A DRAT is a crystal whose frequency vs. temperature characteristic is determined by controlling the angle of cut about two crystallographic axes in lieu of just one axis.

DRATS include SC, IT and FC cut crystals. For a given frequency and mode a DRAT has more mass that an AT Cut resonator making it less susceptible to the frequency altering effects of gravity, acceleration, vibrating, contamination, and shock. DRATs also exhibit lower phase noise that AT Cut resonators.

The upper turn or inversion point for a DRAT is typically between +65 deg. C and 95 deg. C and the frequency vs. temperature deviation in that range is minimal. DRATs provide superior performance over AT Cut resonators in terms of resistance to mechanical forces, absolute frequency stability, phase noise and aging. Applications include very high precision timing references, typically oven controlled crystal oscillators OCXO.

Superior Performance characteristics of DRATs vs. AT Cut resonators are:

Ultra-high stability
Low Phase Noise
Higher Drive Capability
Higher Multiplication Capability
Higher Q
Lower Aging & Hysteresis
Lower G tip-over shift
Higher Vibration vs. Frequency Stability
Faster Warm-up
Oven-less Operation

Comparison of SC and AT-cuts

Desired f vs. T of SC-cut Resonator

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