Image sensor with test circuit

A test method of an image sensor for converting an analog signal generated in each of a plurality of pixels into a digital signal using a counter in an analog-to-digital converter, the test method comprising:

• generating a count clock signal based on a test code that is received in response to a test mode signal;
• changing a reset code to output different values for each horizontal time period, wherein the reset code comprises a first counting value according to the count clock signal in a reset time period of a test mode;
• counting the count clock signal according to the reset code;
• comparing a second counting value with the test code, wherein the second counting value is obtained by subtracting the reset code from an image code, and wherein the image code is a counting value during a signal time period of the test mode;
• and
• outputting a comparison result between the second counting value and the test code through a test terminal.

A test circuit for a counter of an image sensor, the test circuit comprising:

• a test pattern generator that is configured to receive a test code from an external circuit when in a test mode;
• a clock controller that is configured to generate a count clock signal, generate a count enable signal corresponding to the test mode, and periodically change a reset code based on the counter, wherein changing the reset code comprises determining a value of the reset code at least in part by:
• determining a first counting value during reset time period by counting the count clock signal during the reset time period among time periods of the count enable signal;
• and
• assigning the determined first counting value as the value of the reset code;
• and
• a comparison logic that is configured to output a comparison result between an output counting value according to the count clock signal and the test code based on the reset code.