A circuit and method measure the output voltage of a CMOS pixel in a manner that
substantially reduces all columnar pattern noise due to mismatches in the signal
processing circuits including the correlated double sampling amplifiers and A/D
converters. The circuit includes a test switch, operatively connected between a
reference voltage source and a correlated double sampling amplifier, for applying
a test voltage from the reference voltage source when the state of the test switch
is ON to the correlated double sampling amplifier. The reference voltage source
produces a voltage corresponding to a full-scale voltage level to enable the determination
of a gain error in the correlated double sampling amplifier and/or A/D converter;
a voltage corresponding to ground to enable the determination of an offset error
in the correlated double sampling amplifier and/or A/D converter; and a plurality
of analog voltages ranging from analog ground to a full-scale voltage level to
enable the determination of non-linearity errors in the A/D converter.
