Microlensed focal plane array (FPA) using sub-pixel de-selection for improved operability
View Patent ↗A cost-effective FPA includes a plurality of detectors per pixel, wherein radiation is directed by a microlens array into respective focal regions that are covered by the union of the detectors' collections regions within each pixel and any defective detectors are de-selected in the ROIC. The operability of each pixel is evaluated, and a map generated specifying detector de-selection for each pixel. This map is read into memory in the ROIC to de-select bad detectors. Bad detectors are preferably allowed to float to a photovoltage and re-emit some of their accumulated photo charge to neighboring detectors to improve collection efficiency. The radiation levels are preferably read out on a pixel-by-pixel basis. Accordingly, the signals from the selected detectors are combined within each pixel.
1. A focal plane array (FPA) having an array of pixels, wherein each pixel comprises:
a plurality of radiation detectors, each detector having a collection region, the detectors' collection regions overlapping within each said pixel;
a lens element that concentrates incident radiation into a focal region that is covered by a union of the detectors' collection regions; and
a plurality of switch elements connected to respective detectors, each said switch element being switchable between a first state for transmitting a signal received from its corresponding detector to an output and a second state for blocking transmittal of the signal for a de-selected detector,
wherein when the switch element is in the second state the de-selected detector floats to a photovoltage and re-emits some of its accumulated photo charge into the neighboring detectors within the pixel.
2. The FPA of claim 1 , wherein each pixel further comprises:
a summing circuit that sums the transmitted signals to form a pixel signal.
3. The FPA of claim 1 , wherein the switch elements for each pixel are switched in accordance with a map of bad radiation detectors such that the bad radiation detectors are de-selected.
4. The FPA of claim 3 , wherein each switch element comprises:
a switch that is switchable between said first and second states;
in-pixel memory for storing a map value for the corresponding sub-pixel detector; and
a de-select address circuit that is responsive to the map value to control said switch.
5. The FPA of claim 1 , wherein the shape of the lens element is independent of the selection or de-selection of any of said detectors with each said pixel.
6. The FPA of claim 5 , wherein the lens element concentrates the incident radiation into substantially uniform focal regions across the plurality of detectors in each pixel.
7. The FPA of claim 1 , wherein the focal region does not lie completely within the collection region of any one of the radiation detectors within each said pixel.
8. The FPA of claim 1 , wherein the number of detectors in said array exceeds the number of lens elements in said array.
9. The FPA of claim 1 , wherein said detectors are off-center of the focal region for the respective pixels.
10. A focal plane array (FPA), comprising:
a pixilated detector array including a plurality of radiation detectors in each pixel, said detectors having overlapping collection regions with each pixel;
a microlens array including lens elements that concentrate incident radiation into respective focal regions that are covered by a union of the detectors' overlapping collection regions within each pixel;
and a ROIC that includes for each pixel:
a summing circuit; and
a plurality of switch elements connected between respective detectors and the summing circuit, each said switch element being switchable between a first state for transmitting a signal received from its corresponding detector to the summing circuit and a second state for blocking transmittal of the signal while allowing the de-selected detector to float to a photovoltage and re-emit some of its accumulated photo charge into the neighboring detectors within the pixel.
11. The FPA of claim 10 , wherein the switch elements for each pixel are switched in accordance with a map of bad radiation detectors such that the bad radiation detectors are de-selected.
12. The FPA of claim 11 , wherein each switch element comprises:
a switch that is switchable between said first and second states;
in-pixel memory for storing a map value for the corresponding sub-pixel detector; and
a de-select address circuit that is responsive to the map value to control said switch.
13. The FPA of claim 10 , wherein the shape of the lens elements is independent of the selection or de-selection of any of said detectors with each said pixel.
14. The FPA of claim 13 , wherein the lens elements concentrate the incident radiation into substantially uniform focal regions across the detector array.
15. A method for operating a focal plane array (FPA), comprising:
providing a pixilated FPA having a plurality of detectors per pixel, each said detector having a collection region;
directing radiation incident into respective focal regions that are covered by a union of the detectors' collection regions with each pixel, wherein the detectors' collection regions overlap within each pixel;
de-selecting bad detectors;
allowing the bad detectors to float to a photovoltage to re-emit accumulated charge to neighboring detectors within the pixel;
combining output signals from the remaining detectors within each pixel to form pixel output signals; and
reading out the pixel output signals to form an output image.
16. The method of claim 15 , further comprising:
storing a map of bad detectors in said FPA, and de-selecting the bad detectors in accordance with the map.
17. The method of claim 16 , further comprising:
testing the FPA to determine defective detectors in the FPA; and updating the map stored in the FPA.
18. The method of claim 15 , wherein the incident radiation is directed into the respective focal regions independent of the de-selecting of bad detectors.