Imaging systems having column readout circuitry with test data injection capabilities

A method of operating an image sensor to generate an image frame, wherein the image sensor comprises an array of image pixels arranged in rows and columns and a column readout circuit coupled to a given column of the array, wherein the column readout circuit comprises column memory coupled to the given column of the array via a column switch, the method comprising:

• with test data injection circuitry in the column readout circuit, enabling the column switch;
• with the column memory, storing pixel values generated by image pixels in the given column of the array while the column switch is enabled;
• with the test data injection circuitry, disabling the column switch;
• and
• with the test data injection circuitry, injecting test data bits onto the column memory while the column switch is disabled.

A system, comprising:

• a central processing unit;
• memory;
• input-output circuitry;
• and
• an imaging device, wherein the imaging device comprises:
• an array of image pixels arranged in rows and columns;
• and
• column readout circuitry coupled to the array via a plurality of column readout lines, wherein the column readout circuitry comprises:
• reset memory;
• subtraction circuitry;
• test data injection circuitry, wherein the test data injection circuitry is configured to provide a first set of test bits to the reset memory and a second set of test bits to the subtraction circuitry, wherein the reset memory is configured to provide the first set of test bits to the subtraction circuitry while the subtraction circuitry receives the second set of test bits, and wherein the subtraction circuitry is configured to generate test data by performing a subtraction operation using the first and second sets of test bits;
• and
• output memory, wherein the output memory is configured to store rows of an image frame having rows and columns, wherein at least one row of the image frame is formed from the test data and at least one row of the image frame is formed from pixel data generated by the image pixels.