Abstract: An obstacle layer is grown on an inner surface of a mask structure defining a first opening over a first area assigned to a thick field oxide layer during a growth of the thick field oxide layer, and prevents a silicon substrate beneath a peripheral area of the thick field oxide layer from a dopant impurity implanted through the thick field oxide layer into the silicon substrate beneath the central area of the thick field oxide layer so that a channel stopper is never exposed to a major surface of the silicon substrate outside of the thick field oxide layer.

Abstract: A compandor converts a linear code signal consisting of a polarity bit and a plurality of absolute value bits. The polarity bit represents the polarity of each sample value of an original analog signal. The absolute value bits represent the absolute value of the sample. The compandor converts the linear code into a nonlinear code including the polarity bit, a plurality of segment bits representing the segments in a characteristic curve to which the original analog signal belongs, and mantissa bits which indicate the position of the sample value in that segment.