Importance

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Abstract

A signal conversion circuit is provided for obtaining quantized pattern data indicating a variation of photoelectric signal amplitudes along photosensor arrays by a variable pulse width signal indicating the amplitude of the photoelectric signal from each photosensor. A difference detector detects differences in pulse width of the variable pulse width signals to be compared to determine the extent of the variation with a predetermined unit precision. A comparison device determines whether or not the difference in pulse width exceeds a selected number of difference units and the pattern data indicating the variation are supplied only if the difference exceeds the selected number. Consequently, even if there are errors in the circuit elements constituting the signal conversion circuit, correct pattern data free from influence of such errors can be supplied. If the influence of an error on the circuit elements is to be compensated, a device is provided to determine the precision of the pattern data based on the purpose of the conversion circuit. Therefore, the precision of the pattern data can be kept at the highest possible level. The pulse width difference detector and the comparison device each operate as a quantizing system to convert the variable pulse width signal into a quantized signal at the same time so that it is not necessary to supplement the circuit with a circuit element for initiating operation.

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