Calibration method for fingerprint sensor and display device using the same

1. A calibration method for calibrating a fingerprint sensor comprising a plurality of photosensors, the calibration method comprising:

generating calibration data through white calibration and dark calibration; and

applying offsets to the plurality of photosensors using the calibration data,

wherein the white calibration comprises first, second and third white calibration operations of measuring received light amounts corresponding to first, second and third brightness values, respectively,

wherein the dark calibration comprises first, second and third dark calibration operations of measuring received light amounts corresponding to the first, second and third brightness values, respectively, and

wherein the third brightness value of a plurality of light-emitting elements is higher than the second brightness value, and the second brightness value is higher than the first brightness value.

2. The calibration method according to claim 1 , wherein:

the fingerprint sensor further includes a substrate, a light-blocking layer located on a first surface of the substrate and having openings formed in a light-blocking mask, and a sensor layer located on a second surface of the substrate and having the plurality of photosensors, and

generating the calibration data comprises disposing a first reflector having a flat reflective surface on the first surface of the substrate so that the first reflector overlaps the sensor layer in a thickness direction.

3. The calibration method according to claim 2 , wherein:

the first reflector comprises a skin color reflector and a black reflector, and

the white calibration is performed using the skin color reflector, and the dark calibration is performed using the black reflector.

4. The calibration method according to claim 2 , wherein:

a light-emitting element layer is located on the light-blocking layer and has the light-emitting elements,

the white calibration comprises the first, second and third white calibration operations of measuring the received light amounts of the sensor layer corresponding to the first, second and third brightness values of the light-emitting elements, respectively, and

the dark calibration comprises the first, second and third dark calibration operations of measuring the received light amounts of the sensor layer corresponding to the first, second and third brightness values of the light-emitting elements, respectively.

5. The calibration method according to claim 2 , wherein a light reception period of the sensor layer in the white calibration is longer than a light reception period of the sensor layer in the dark calibration.

6. The calibration method according to claim 4 , wherein a light reception period of the sensor layer in the first white calibration operation is longer than a light reception period of the sensor layer in each of the second and third white calibration operations.

7. The calibration method according to claim 4 , wherein generating the calibration data further comprises:

measuring a received light amount of the sensor layer in each of the first, second and third white calibration operations and in each of the first, second and third dark calibration operations; and

determining whether a corresponding calibration operation is a normal operation by checking whether the measured received light amount of the sensor layer is within a preset range.

8. The calibration method according to claim 7 , wherein the preset range is designated such that a brightness value corresponding to the received light amount of the sensor layer, which is higher than a reference brightness value by a threshold amount, is set as an upper limit and such that the brightness value corresponding to the received light amount of the sensor layer, which is lower than the reference brightness value by the threshold amount, is set as a lower limit.

9. The calibration method according to claim 8 , wherein a panel driver configured to control brightness values of the light-emitting elements is used.

10. The calibration method according to claim 9 , further comprising:

generating a test image of a second reflector comprising an uneven reflective surface with an irregularity based on sensing signals provided from the photosensors;

detecting a shape of the irregularity of the second reflector by calibrating the test image using the calibration data;

performing a noise checking operation of determining whether generation of the calibration data is normally performed based on the shape of the irregularity of the second reflector; and

resetting the panel driver when the received light amount of the sensor layer is outside of the preset range.

11. A program storage device tangibly embodying a program of non-transient instructions executable by a processor for calibrating a fingerprint sensor, the instructions comprising:

generating calibration data through white calibration and dark calibration; and

applying offsets to a plurality of photosensors based on the calibration data,

wherein the white calibration is performed using a substantially skin-colored reflector and the dark calibration is performed using a substantially gray-colored reflector,

wherein white calibration comprises first, second and third white calibration operations of measuring received light amounts corresponding to first, second and third brightness values, respectively,

wherein the dark calibration comprises first, second and third dark calibration operations of measuring received light amounts corresponding to the first, second and third brightness values, respectively, and

wherein the third brightness value of a plurality of light-emitting elements is higher than the second brightness value, and the second brightness value is higher than the first brightness value.