Patent Abstract:
A cover for an image sensor array is disclosed. The cover includes a plate formed of substantially transparent material and placed adjacent to the image sensor array. The plate has a plurality of surfaces and forms a lensing structure. At least one of the plurality of surfaces is contoured into a lensing surface capable of performing an imaging improvement or enhancement function.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 09/470,284, filed on Dec. 22, 1999 now U.S. Pat. No. 7,133,076, which is incorporated herein by reference. This application claims benefit of the priority of U.S. Provisional Application Ser. No. 60/113,850, filed Dec. 24, 1998 and entitled “Contoured Surface of Image Plan Array Cover Plate.” 
    
    
     BACKGROUND 
     The present specification generally relates to image sensor arrays, and particularly to a contoured-surface cover plate for such image sensor arrays. 
     When a sensor array is mounted on an image sensor assembly such as a digital camera system, the sensor array is sealed for protection by bonding a cover plate on the assembly over the sensor array. Often, the cover plate is a flat piece of transparent material, such as glass, plastic or plexiglass, which provides protection only from the environment. The cover plate offers little in terms of optical enhancement. 
     On the other hand, competition for cheap camera systems is driving demand for high quality optics at a low price. However, such high quality optics are difficult to design and fabricate without the use of multiple lensing elements. Therefore, the use of multiple lensing elements often drives the price up. In addition, the lensing elements, once fabricated, must be mounted and aligned to the camera system at fairly tight tolerances in positioning, focus, and attitude. This also adds to the overall cost of the camera system. 
     SUMMARY 
     The techniques described herein obviate, the above described difficulties by deterministically contouring the optically-flat cover plate. The contouring allows for the use of the cover plate as an additional lensing element. The placement of the contoured cover plate in the optical path of an incident light converts a singlet lens system into a doublet system, a doublet system into a triplet system, and so on. 
     The contouring of the cover plate also allows using the plate as mounting structures for the lensing elements, such as lenses, filters, and polarizers. The mounting structures can have alignment marks which are used to automatically align and secure the lensing elements. Furthermore, the contouring of the cover plate enhances the ability of the lensing element to correct the aberration of Petzval field curvature. The aberration is the natural tendency for a lens to produce its image on a curved rather than a flat focal plane. Therefore, the placement of the contoured cover plate close to the image sensor often reduces this aberration. 
     A lensing structure may include lensing elements, mounting structures, and alignment marks. 
     In one aspect, the present specification involves a cover for an image sensor array. The cover includes a plate formed of substantially transparent material and placed adjacent to the image sensor array. The plate has a plurality of surfaces and forms a lensing structure. At least one of the plurality of surfaces is contoured into a lensing surface capable of performing an imaging improvement or enhancement function. 
     In another aspect, an image sensor camera system for converting optical data into digital image data is described. The camera system includes a lens system, an image sensor array, and sensor electronics. 
     The lens system carries and focuses the optical data onto the image sensor array. The lens system includes a plurality of lenses and a cover plate. The cover plate is contoured into a lensing structure for imaging improvement and enhancement function. 
     The image sensor array has a plurality of sensors. The sensors receive the optical data and integrate the data into electrical charge proportional to the amount of optical data collected within a particular period of time. The sensor electronics receive the electrical charge and converts the electrical charge received by the plurality of sensors into digital image data. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other embodiments and advantages will become apparent from the following description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects will be described in reference to the accompanying drawings wherein: 
         FIG. 1A  is an exploded view of a cover plate; 
         FIG. 1B  is a side view of the cover plate cut along the plane  1 - 1  indicated in  FIG. 1A ; 
         FIG. 1C  is another embodiment of the cover plate contoured into a positive lens with convex protuberance; 
         FIG. 2A  is one embodiment of an existing three-element lens system; 
         FIG. 2B  is the lens system of  FIG. 2A  inserted into the cover plate; 
         FIG. 3A  is a diffraction grating blazed onto the surface of the cover plate; 
         FIG. 3B  is a diffraction grating blazed on a concave depression; 
         FIG. 3C  is a diffraction grating blazed on a convex protuberance; 
         FIG. 4A  is an injection molded cover plate having a post and a convex lensing surface; 
         FIG. 4B  is an injection molded cover plate having a post and a concave lensing surface; 
         FIGS. 5A and 5B  show top views of the cover plates including mounting structures; 
         FIGS. 5C through 5H  show different embodiments of the mounting structure from the side; 
         FIGS. 6A through 6C  show different embodiments of the cover plate having a combination of lensing elements and mounting structures; 
         FIG. 7A  is a cut-away side perspective view of an image sensor camera system; and 
         FIG. 7B  is a block diagram of the image sensor camera system. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A detailed description of the contoured surface of an image sensor array cover plate is herein provided with respect to the figures. 
       FIG. 1A  shows an exploded view of a cover plate  100  placed in front of an image sensor array  102 . The image sensor array can be an array of active pixel sensors. Each active pixel sensor includes a photoreceptor, e.g., a photodiode or photogate, an in-pixel follower transistor, and an in-pixel selector transistor. The cover plate  100  is contoured to act as an additional lensing element  104 . The lensing element  104  operates to enhance the focusing of light onto the image sensor array  102 . 
       FIG. 1B  shows a side view of the cover plate  100  cut along the plane  1 - 1  indicated in  FIG. 1A . The cover plate  100  is contoured into a negative lens with concave depression  106  and is placed in front of the image sensor array  102  to focus the light falling onto the sensor array  102 . 
       FIG. 1C  shows another embodiment of the cover plate  108  contoured into a positive lens with convex protuberance  110 . The cover plate  108  is placed in front of the sensor array  102 . 
       FIG. 2A  shows one embodiment of an existing three-element lens system  200 . The lens system  200  includes a first convex lens  202 , a second plano-concave lens  204 , and a third plano-convex lens  206 . The lens system  200  also includes a lens mount  208 , a threaded retaining ring  210 , and a guide tab  212 . Light enters the lens system  200  from the direction indicated as  214 . 
       FIG. 2B  illustrates the lens system  200  inserted into a cover plate  214 . The cover plate  214  can have a mounting structure  218  attached to the front surface  222 . In another embodiment, the cover plate  214  can be a single-piece injection molded structure that includes the mounting structure  218 . 
     The lens system  200  can be inserted into the cover plate  214  by threading it into the mounting structure  218 . The threaded retaining ring  210  on the lens mount  208  is guided into a threaded ring  220  on the mounting structure  218  to lock the lens system  200  onto the cover plate  214 . In an alternative embodiment, the lens system  200  can be secured onto the cover plate  214  by locking the guide tab  212  on the lens mount  208  onto the cover plate  214  using an alignment mark  216 . 
     Once the three-element lens system  200  is firmly secured to the cover plate  214 , the combination effectively forms a four-element lens system comprising the three lenses  202 ,  204 ,  206  in the lens system  200  and a contoured surface  226  of the lens  224  formed by the cover plate  214 . Furthermore, the contoured lens  224  enhances the ability of the four-element lens system to correct the aberration of Petzval field curvature. The aberration is the natural tendency for a lens to produce its image on a curved rather than a flat focal plane. Therefore, the placement of the contoured cover plate  214  close to the image sensor  102  often reduces this aberration inherent in flat cover plates. 
       FIG. 3A  shows a diffraction grating  302  blazed onto the surface of a cover plate  300 . The diffraction grating  302  performs similar imaging improvement function to the refractive lens system in  FIG. 2B . Therefore, the cover plate  300  with the diffraction grating  302  formed on its surface acts as a diffractive lensing element  316 . 
     In another embodiment, hybridization of refractive and diffractive profiles is formed on a cover plate  304 .  FIG. 3B  shows a diffraction grating  306  blazed on a concave depression  308  formed on the cover plate  304 . The concave grating  306  can be manufactured using ruling and holographic techniques. The concave grating forms a hybrid refractive-diffractive lensing element  318 . 
     In a further embodiment, shown in  FIG. 3C , a diffraction grating  312  is formed on a convex surface  314  of a cover plate  310 . The convex grating  312  can be manufactured using a similar is technique used for the concave grating  306  shown in  FIG. 3B . The convex grating forms a hybrid refractive-diffractive lensing element  320 . 
       FIG. 4A  shows an injection-molded cover plate  400  having a post  402  and a convex lensing surface  404 . The post  402  and the lensing surface  404  form a complete lens system and thereby eliminate the need for additional lenses. The post  402  and the lensing surface  404  are formed over the sensor array region  406  to direct the light onto the sensor array  102 . The post  402  and the lensing surface  404  form a lensing element  408 . 
     In an alternative embodiment, shown in  FIG. 4B , the lensing surface  410  can be contoured as a concave depression forming a lensing element  412 . 
       FIGS. 5A through 5H  show several different embodiments of a mounting structure  500 ,  502 . The mounting structure  500 ,  502  is formed over the sensor array. The mounting structure  500 ,  502  is configured to allow the lens system to be easily and quickly mounted onto the cover plate  504 . 
       FIG. 5A  shows a top view of the cover plate  504  including the mounting structure  500  formed on the top surface  506  of the cover plate  504 . In this embodiment, the mounting structure  500  forms a square pattern, which allows a square-shaped lens mount to be mounted securely to the mounting structure  500 .  FIG. 5B  shows a circular-shaped mounting structure  502  formed on the surface  506  of the cover plate  504 . 
       FIGS. 5C through 5H  show several different embodiments of the mounting structure  500  from the side. The side views are formed by slicing the cover plate  504  along the line  5 - 5 . 
       FIG. 5C  shows a mounting structure formed with a mesa-like protrusion  508  on the surface  510  of the cover plate  504 . The protrusion  508  can be a clear material attached to the front surface of the cover plate  504  or injection molded into a single-piece cover plate  504 . The protrusion  508  can have a threaded retaining ring on the outside wall for easy insertion, focus and removal of the lens system. 
       FIG. 5D  shows a variation of the mounting structure shown in  FIG. 5C . The mounting structure in  FIG. 5D  can be formed with a hollowed-out mesa-like protrusion or a ringed-wall structure attached to the cover plate  504 . 
       FIGS. 5E and 5F  show two variations of the ringed mounting structure  512  shown in  FIG. 5D .  FIG. 5E  shows a threaded retaining ring  514  on the outside wall of the ringed structure  512 .  FIG. 5F  shows the threaded retaining ring  514  on the inside wall of the ringed structure  512 . The threaded retaining ring  514  is used to mount and securely attach the lens mount to the mounting structure  512 . 
       FIGS. 5G and 5H  show a mounting structure formed with a well-like depression  516  in the cover plate  504 . The depression  516  can be used to lock the lens mount onto the cover plate  504 .  FIG. 5H  also shows a threaded retaining ring  518  on the side wall of the well-like depression  516  for locking the lens mount. 
       FIGS. 6A through 6C  show different embodiments of the cover plate having a combination of lensing elements and mounting structures. 
       FIG. 6A  shows a cover plate  600  having a lensing element  608  and a mounting structure  604 . The lensing element  608  is formed with a concave lensing surface  602 . The mounting structure  604  can have a threaded retaining ring  606  on the inside or outside wall of the mounting structure  604 . 
       FIG. 6B  shows another combination of a lensing element  616  and a mounting structure  612 . The lensing element  616  is formed with a post  618  and a convex lensing surface  614  at the top of the post  618 . 
       FIG. 6C  shows a combination of a ringed mounting structure  622  and a lensing element  620  in the middle. The lensing element  620  is formed with a post  624  and a convex lensing surface  626 . 
       FIG. 7A  shows a cut-away side perspective view of an image sensor camera system  700 . The camera system can be an active pixel sensor (APS) system or a charge-coupled device (CCD) system. The camera system  700  includes a lens system  708 , a cover plate  702 , an image sensor array  704 , and sensor electronics  706 . 
     The lens system  708  includes a plurality of lenses  714  mounted on a lens mount  710 . The lens system  708  may also include other lensing elements, such as a filter or a polarizer  712 . The contoured cover plate  702  acts as an additional lensing element. 
       FIG. 7B  shows a block diagram of the image sensor camera system  700 . The camera system  700  receives optical image data  716 . The optical data  716  are focused by the lens system  708  and the contoured cover plate  702  onto the image sensor array  704 . The sensor electronics  706  converts electrical charge falling on the sensor array  704  to digital image data  718 . 
     Although only a few embodiments have been described in detail above, those of ordinary skill in the art certainly understand that modifications are possible. For example, a contouring can be done on both surfaces of the cover plate. Also, while the preferred aspect shows only a square and a circular mounting structures, mounting structures of other shapes are possible, such as a hexagonal- or octogonal-shaped mounting structure. In addition, other alignment marks or lens locking mechanisms can be used on the cover plate to securely attach the lens system to the cover plate. All such modifications are intended to be encompassed within the following claims, in which:

Technology Classification (CPC): 7