A radiation-hard AGC stabilized SOS crystal oscillator

A 12 MHz crystal oscillator/divider fabricated in silicon on sapphire (SOS) is presented. The chip incorporates a significant analog component, as an automatic gain control (AGC) loop is used to minimize the influence of changing transistor parameters due to radiation. The design tackles the problems associated with realizing analog circuitry in a floating substrate technology and the use of circuit techniques to achieve radiation hardness. A simple system-level modeling method is used to predict the oscillator start-up and AGC loop stability. The measured stability is around 0.1 p.p.m./V; circuits are still functional at more than 50 Mrad (Si) and show frequency deviations of typically 8 p.p.m. from nominal.<
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