Under display optical fingerprint sensor arrangement for mitigating moiré effects

1. An electronic device for imaging a biometric object having structural features of interest, comprising:

a display including rows of pixel elements, the rows of pixel elements being parallel to a first primary direction along a first axis; and

an optical sensor disposed underneath the display, the optical sensor being parallel to a second primary direction along a second axis,

wherein the second axis has an angle relative the first axis and wherein the angle adjusts a moiré pattern frequency outside of a frequency range corresponding to the structural features of interest to reduce moiré effect on images when imaging the biometric.

2. The electronic device of claim 1 , wherein the biometric object is a finger and the frequency range of the structural features of interest corresponds to a frequency of ridges and valleys.

3. The electronic device of claim 1 , wherein the angle is between 20 and 30 degrees.

4. The electronic device of claim 1 , wherein the angle is between 26 and 27 degrees.

5. The electronic device of claim 1 , wherein the optical sensor includes an optical element having rows of apertures and a sensor array having rows of sensing elements, the rows of apertures and rows of sensing elements being parallel to the second axis.

6. The electronic device of claim 1 , wherein the optical sensor includes an optical element having rows of apertures and a sensor array having rows of sensing elements, the rows of apertures being parallel to the first axis and the rows of sensing elements being parallel to the second axis.

7. The electronic device of claim 1 , wherein the optical sensor includes an optical element having rows of apertures and a sensor array having rows of sensing elements, the rows of apertures being parallel to the second axis and the rows of sensing elements being parallel to the first axis.

8. The electronic device of claim 1 , wherein the optical sensor includes an array of sensing elements mounted on a die, the die having a primary axis parallel to the first axis and the array of sensing elements having a primary axis parallel to the second axis.

9. An electronic device, comprising:

a display having rows of pixel elements parallel to a first primary axis; and

an optical sensor having rows of sensing elements parallel to a second primary axis, the optical sensor configured to image a fingerprint,

wherein the optical sensor is disposed underneath the display and oriented such that the second primary axis is rotated relative to the first primary axis at an angle θ, the angle θ being sufficient to reduce moiré effect on images when imaging the fingerprint.

10. The electronic device of claim 9 , wherein the angle θ is sufficient to reduce a pattern of the moiré effect by an order of magnitude as compared to a non-rotated optical sensor.

11. The electronic device of claim 9 , wherein the rows of sensing elements are disposed on a die, the die having a third primary axis parallel to the first primary axis and the rows of sensing elements being parallel to the second primary axis.

12. The electronic device of claim 9 , wherein the angle θ is between 20 and 30 degrees.

13. The electronic device of claim 9 , wherein the angle θ is 27 degrees.

14. The electronic device of claim 9 , wherein the optical sensor further comprises a collimator and wherein the optical sensor is further orientated to reduce moiré effect on images caused by openings in the collimator.

15. A method for determining an angle to mount an optical sensor relative to a display to mitigate moiré patterns, comprising:

determining a frequency of components of the display;

determining a frequency of components of the optical sensor;

determining a frequency of moiré patterns reaching the optical sensor when mounted below the display; and

determining the angle based on the frequency of the components of the display and the frequency of the components of the sensor, wherein the angle adjusts the frequency of the moiré patterns to reduce moiré effect on images when imaging a biometric.

16. The method of claim 15 , further comprising:

determining a frequency of features of interest, the features of interest corresponding to structural features of an input object;

wherein the step of determining the angle includes selecting the angle to adjust the frequency of moiré patterns above or below the frequency of the features of interest.

17. The method of claim 16 , wherein the step of determining the angle includes selecting the angle such that the frequency of moiré patterns are an order of magnitude higher or lower than the frequency of features of interest.

18. The method of claim 15 , wherein the angle is between 25 and 30 degrees.

19. The method of claim 15 , wherein the step of determining the frequency of components of the display further comprises determining a frequency of pixels and sub-pixels.

20. The method of claim 19 wherein the step of determining the frequency of components of the display further comprises determining a frequency of electrodes.