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In this paper, measurement results for a micropower 2MHz CMOS frequency reference circuit fabricated with a ml2 13 M7 M5 M6 M8 :Ml8 M19 0.13 ,um CMOS process are presented. This frequency reference circuit, based on source-coupled CMOS multivibrator, provides M14 m 2 M22 the clock signal for a read-out circuit of a capacitive sensor. In Cm addition to a low power consumption, a good frequency stability M15 OUT is required. Supply independent biasing and symmetrical loads are used to optimize the frequency stability. The typical power C X16 M17 consumption is 3.0 ,uW at room temperature with 1.8 V supply _ voltage. When properly calibrated, the frequency stays within M(MlM 2 2 ±2.5% of the nominal oscillation frequency in the operating Rm voltage range of 1.8 -2.5 V (with ±10 % variation) over a temperature range from -35 to +85 C. The measured phase BIASINGCIRCUIT OSCILLATOR COMPARATOR noise and jitter agree well with the simulations.Fig. 1. Presented frequency reference circuit.

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Retinal detachments have a tendency to occur more commonly in spring and summer than in winter. Two new series are presented here, the first collected in Northern Finland at latitudes 64 degrees-70 degrees and the second from Novosibirsk, at a much lower latitude, 55 degrees N, but with an equally long winter. A statistically significant seasonal variation is found in both. The highest incidence peak is seen in June in Oulu and in July in Novosibirsk, the difference between the prevalence curves was, however, not statistically significant. The Oulu series shows a statistically highly significant seasonal variation in low refractive errors but no seasonal difference in high myopia and aphakia.

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