An image sensor including: a plurality of phase shift code generators, wherein each of the plurality of phase shift code generators outputs a phase shift code; a test data selection circuit for outputting test data corresponding to a test pattern; a counter for receiving the phase shift code from at least one of the plurality of phase shift code generators, receiving the test data from the test data selection circuit, latching a digital code corresponding to the test pattern using the phase shift code, and outputting the digital code; and a control logic for calculating a data pattern using the digital code and selecting one of the plurality of phase shift code generators in accordance with a result of a comparison between the data pattern and the test pattern.