PURPOSE: To make it possible to readuce decision circuits and expectation generating circuits in the multilevel output circuit of especially a liquid-crystal display unit, by making a comparison between the output of a checked article an that of a standard article with the same function.
CONSTITUTION: pattern generating circuit 1 forms sequentially test patterns needed for inspection and the same signal is inputted to checked article 2 and standard article 3 which is of the same kind as the checked article and of good quality found by checking, and corresponding outputs are inputted to subtracter circuits 4 and 4' to obtain a difference in output voltage between checked article 2 and standard article 3. Voltage comparator circuit 5 and 5' compare this voltage difference with a positive allowable value and voltage comparator circuits 6 and 6' make a comparison with a negative allowable value, so that when either one exceeds allowable values, a high-level defective signal will be sent out. Then, logic circuit 7 decides that the checked article is of normal quality when those outputs are all low in level.
OOMORI ISAO
SATOU YOSHINOBU
