Abstract:
A lens unit includes a lens having a focal length variable responsive to an applied electrical field, and an electrical connector. The electrical connector is a flexible circuit element that connects the lens to an electrical power supply.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a lens unit, and more particularly, but not exclusively, to a lens unit comprising flexible circuitry, such as for a digital camera integrated into a mobile telephone.  
       BACKGROUND OF THE INVENTION  
       [0002]     Liquid lenses having a variable focal length that varies with a voltage applied across them are used in digital cameras for mobile telephones. However, in a typical digital camera in a mobile telephone, electrical connections to the terminals of a liquid lens have a high failure rate.  
         [0003]     A number of connection schemes have been used in the manufacture of mobile telephone cameras. One current connection scheme involves the routing of copper tracks inside channels formed in an injection molded mount. This connection scheme is expensive and complex to manufacture. Also, there is a high yield failure rate associated with this connection scheme.  
         [0004]     An alternative connection scheme involves the soldering of wires between the substrate and the lens unit. This is unreliable due to the brittleness of the soldered connection, and is also costly to assemble. A further connection scheme employs resilient copper spring contacts to contact the terminals of the lens unit to a voltage supply. This arrangement is difficult and expensive to process manufacture.  
       SUMMARY OF THE INVENTION  
       [0005]     According to a first aspect, a lens unit comprises a lens having a focal length variable responsive to an applied electric field, and an electrical connector to connect the lens to an electrical power supply. The electrical connector may comprise a flexible circuit element.  
         [0006]     The use of a flexible circuit element simplifies the manufacture of the lens unit as compared to prior art connection arrangements, and may also reduce the failure rate. This is because the modes of failure associated with the prior art arrangements are at least partially removed by the use of a flexible circuit element.  
         [0007]     The lens may comprise a liquid lens. The lens may comprise first and second terminals. The electrical connector may be arranged to connect either, or both, of the first and/or second terminals to the electrical power supply. The electrical connector may be connected to either, or both, of the first and/or second terminals by an electrically conducting adhesive. The electrical connector may be connected to an output of the electrical power supply by an electrically conducting adhesive. The use of an electrically conducting adhesive simplifies the processing required as compared to the prior art arrangements.  
         [0008]     The flexible circuit element may comprise an electrical component and/or a circuit. The electrical components may comprise a passive electrical component. The circuitry may comprise a drive circuit. The provision of passive components and/or drive circuits on the flexible circuit allows these components to be removed from a substrate, thereby yielding greater substrate area for other signal processing applications.  
         [0009]     According to a second aspect, an electronic device comprises a lens unit according to the first aspect. The electronic device may comprise any of the following: digital still camera, digital video camera, mobile telephone, web-cam, and an endoscope.  
         [0010]     These and other aspects of the present invention will be apparent and more clear with reference to the embodiments described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0012]      FIG. 1  is a side view of a sensor unit comprising a lens unit according to the present invention;  
         [0013]      FIG. 2  is a cut-away perspective view of the lens unit of  FIG. 1 ;  
         [0014]      FIG. 3  is a perspective side view of terminal regions of the lens unit of  FIG. 1 ; and  
         [0015]      FIG. 4  is a side view of a sensor unit comprising a lens unit according to another aspect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring now to FIGS.  1  to  3 , a camera  100  comprises a substrate  102 , an optical stack  104  and a flexible circuit  106 . The substrate  102  comprises a sensor  108 , electrical components  110   a - 110   c,  and positive and negative power supply connections  112   a,    112   b  on the substrate. The optical stack  104  comprises a cylindrical liquid lens  114  and a cylindrical housing  116 . The housing  115  is mounted coaxially with the liquid lens  114 , and between the liquid lens  114  and the substrate  102 .  
         [0017]     The flexible circuit  106  comprises an annular body portion  116  and two rectangular legs  118 ,  120  diametrically opposed to the body portion  116 . The annular body portion  116  is located about the periphery of the liquid lens  114  such that is does not obscure the field of view of the liquid lens  114 . The legs  118 ,  120  extend from the body portion  116  toward the substrate  104  where they are electrically connected to the respective positive and negative power supply connections  112   a,    112   b.  Typically, the legs  118 ,  120  are connected to the power supply connections  112   a,    112   b  by an electrically conductive glue or solder.  
         [0018]     The liquid lens  114  comprises positive and negative terminals  122 ,  124 . In the present embodiment the positive terminal  122  is located on an outer surface  126  of the lens  114 , and the negative terminal  124  is located on a side surface  128  of the lens  114  adjacent the positive terminal  122 . Typically, the flexible circuit  106  is connected to the terminals  122 ,  124  by an electrically conductive glue or solder.  
         [0019]     The liquid lens  114  has a focal length that varies in response to an electric field applied across the positive and negative terminals  122 ,  124  and is arranged to focus incoming electromagnetic radiation, typically visible or infra-red radiation, onto the sensor  108 . The sensor  108  outputs a signal corresponding to the scene focused by the liquid lens to image processing circuitry (not shown).  
         [0020]     With particular reference to  FIG. 3 , it will be appreciated that, in the present embodiment, the positive terminal  122  may be located at any point about the circumference of the outer surface  126 , and the negative terminal  124  may be located at any point about the circumference of the side surface  128 .  
         [0021]     Referring now to  FIG. 4 , the embodiment is substantially the same as that described in relation to FIGS.  1  to  3 . Accordingly, similar parts will be accorded the same reference numerals. The flexible circuit  406  comprises electrical components  430 ,  432 . Typically, the electrical components  430 ,  432  will comprise passive circuit elements as will be known to those skilled in the art. Alternatively or additionally, the electrical components  430 ,  432  may comprise drive circuitry for driving the liquid lens  414 .  
         [0022]     It will be appreciated that in the present embodiment the voltage and currents supplied to the flexible circuit  406  will have to be adjusted to allow for power dissipation by the electrical components  430 ,  432  in order that the correct voltage is supplied to the positive and negative terminals  422 ,  424  to ensure that the desired focusing properties are achieved.  
         [0023]     It will be further appreciated that although described in relation to a liquid lens the present invention is suitable for use with any lens arrangement in which the focal characteristics of the lens vary with an applied electric field.  
         [0024]     While various embodiments of the invention have been described, it will be apparent to those skilled in the art, once given this disclosure, that various modifications, changes, improvements and variations may be made without departing from the scope of the invention.