Image sensor with asymmetric-microlens phase-detection auto-focus (PDAF) detectors, associated PDAF imaging system, and associated method

1. An image sensor with a first asymmetric-microlens phase-detection auto-focus (PDAF) detector, the first asymmetric-microlens PDAF detector comprising:

a first plurality of pixels forming a first sub-array having at least two rows and two columns; and

a first microlens located above each of the first plurality of pixels, and being rotationally asymmetric about an axis perpendicular to the first sub-array, the axis intersecting a first local extremum of a top surface of the first microlens, the first microlens at least partially covering each pixel of the first plurality of pixels and having, in a cross-sectional plane intersecting the first microlens and perpendicular to a top surface of the first sub-array, a height profile having more than one local maximum.

2. The image sensor of claim 1 , capable of capturing an image formed thereon, and further comprising an image data processing unit capable of (i) receiving electrical signals from each of the plurality of pixels, and (ii) outputting data associated with misfocus of the image.

3. The image sensor of claim 1 , the first sub-array being a two-by-two planar array, the height profile having two local maxima.

4. The image sensor of claim 1 , further comprising:

a second asymmetric-microlens PDAF detector including:

a second plurality of pixels forming a second sub-array having at least two rows and two columns, and

a second microlens located above each of the second plurality of pixels and being rotationally asymmetric about a second axis perpendicular to the second sub-array and intersecting a second local extremum of a top surface of the second microlens, the second microlens at least partially covering each pixel of the second plurality of pixels;

the first and second plurality of pixels being part of a pixel array having a pixel-array top surface and a pixel-array center;

the second asymmetric-microlens PDAF detector being further from the pixel-array center than the first asymmetric-microlens PDAF detector;

a location on the pixel-array top surface directly beneath the first local extremum being at a first distance from a center of the first sub-array; and

a location on the pixel-array top surface directly beneath the second local extremum being at a second distance from a center of the second sub-array, the second distance exceeding the first distance.

5. The image sensor of claim 1 ,

the first plurality of pixels each having a respective color filter thereon, each color filter having a transmission spectrum,

the sub-array, by virtue of the transmission spectrum of each color filter, having reflection symmetry with respect to a center of the pixel sub-array.

6. A phase-detection auto-focus (PDAF) imaging system comprising:

an image sensor having a first asymmetric-microlens PDAF detector that includes:

(a) a first plurality of pixels forming a first sub-array having at least two rows and two columns, and

(b) a first microlens located above each of the plurality of pixels and being rotationally asymmetric about an axis perpendicular to the first sub-array, the axis intersecting a first local extremum of a top surface of the first microlens the first microlens at least partially covering each pixel of the first plurality of pixels and having, in a cross-sectional plane intersecting the first microlens and perpendicular to a top surface of the first sub-array, a height profile having more than one local maximum; and

an image data processing unit capable of receiving electrical signals from each of the plurality of pixels and generating a PDAF signal from the received electrical signals.

7. The PDAF imaging system of claim 6 , further comprising an autofocus module capable of receiving the PDAF signal and generating a misfocus signal indicative of a degree of misfocus between the image sensor and an imaging lens that has an optical axis intersecting the image sensor.

8. The PDAF imaging system of claim 6 , the first sub-array being a two-by-two planar array, the height profile having two local maxima.

9. The PDAF imaging system of claim 6 , further comprising:

a second asymmetric-microlens PDAF detector including:

a second plurality of pixels forming a second sub-array having at least two rows and two columns, and

a second microlens located above each of the second plurality of pixels and being rotationally asymmetric about a second axis perpendicular to the second sub-array and intersecting a second local extremum of a top surface of the second microlens, the second microlens at least partially covering each pixel of the second plurality of pixels;

the first and second plurality of pixels being part of a pixel array having a pixel-array top surface and a pixel-array center;

the second asymmetric-microlens PDAF detector being further from the pixel-array center than the first asymmetric-microlens PDAF detector;

a location on the pixel-array top surface directly beneath the first local extremum being at a first distance from a center of the first sub-array;

a location on the pixel-array top surface directly beneath the second local extremum being at a second distance from a center of the second sub-array, the second distance exceeding the first distance.

10. The PDAF imaging system of claim 6 ,

the plurality of pixels each having a respective color filter thereon, each color filter having a transmission spectrum,

the sub-array, by virtue of each transmission spectrum, having reflection symmetry with respect to a center of the pixel sub-array.