Patent ID: 8598901

Claim:
A photoelectric conversion system comprising: a plurality of pixels arranged in a matrix, each pixel including a photoelectric conversion element; a reference signal generating unit configured to generate a reference signal of a signal level changing in a monotonous manner with time; a plurality of A/D converters each arranged correspondingly to each column of the matrix of pixels, to convert analog signals from the plurality of pixels; and a counter configured to perform a count operation according to an output of the reference signal from the reference signal generating unit, and to supply a count signal through a count signal line to the plurality of A/D converters, wherein each of the A/D converters has a comparator configured to compare a signal from a pixel of the plurality of pixels with the reference signal generated by the reference signal generating unit, and a memory unit for storing the count signal from the counter, wherein the photoelectric conversion system further comprises a test circuit connected to the count signal line and provided independently from the plurality of A/D converters, and the test circuit is configured to test the counter, based on a matching of an expected value of the count signal with the count signal supplied through the count signal line from the counter.