"Characterization of 1.2GHz Phase Locked Loops and Voltage Controlled Oscillators in a Total Dose Radiation Environment"
Martin Vandepas, Kerem Ok, Anantha Nag Nemmani, Merrick Brownlee, Kartikeya Mayaram, Un-Ku Moon
Oregon State University
Radiation hardness is an important consideration for Phase Locked Loops (PLLs) intended for space applications. Total dose radiation hardness of analog intensive circuits such as PLLs are of special interest as they do not lend themselves to calibration or redundancy techniques as readily as digital circuitry. This work summarizes measurement results obtained on a set of voltage controlled oscillators (VCOs) and a charge-pump PLL in a total dose radiation environment. The radiation was produced by a calibrated low energy X-ray (LEXR) source with dose rates of 300-500rad(SiO2)/sec. The designs are completed in a 0.35um SOI process without specific design effort to reduce radiation effects. The circuits are all designed to operate nominally at 1.2GHz. They are characterized before and after irradiation with a total dose of 500kRad(SiO2). The VCO's were measured for jitter and tuning range. The tuning range of the passively tuned LC-VCOs remained stable while the range of the actively tuned ring VCOs varied significantly. In addition, a more in depth test was done on the PLL. It was irradiated to 6.2MRad(SiO2). The bias current as well as the tuning range were monitored throughout the test. The PLL was able to lock to a reference even after the 6.2MRad(SiO2) dose. This paper describes the methodology and results of this testing and also presents insight on the design of high speed, rad-hard PLLs.
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