Display System with Independently Controlled Transmissive and Reflective Subpixels and Method of Use

Abstract

A device ( 100 ) includes a display ( 102, 800 ) that is suitable for use under widely ranging lighting conditions. The display includes separately operable transmissive light modulator subpixels ( 402, 404, 406, 502, 504, 506, 602, 604, 606, 702, 704, 706, 808, 810, 812, 1036, 1136, 1204, 1304, 1404, 1504, 1716, 1916 ) that can be provided in at least three colors to provide a full color display but also includes separately operable reflective light modulator subpixels ( 408, 508, 608, 708, 814, 1038, 1138, 1202, 1302, 1402, 1502, 1714, 1914 ) that provide basic readability when light levels are so high (e.g., bright summer day) that the image presented by the transmissive light modulators would be difficult to discern. The reflective light modulators may be provided with in-pixel memory ( 526 ) so as to reduce the energy cost of providing always-on functioning for displaying certain time sensitive information.

We claim: 
     
         1 . A liquid crystal display comprising:
 a 2-D array of subpixels including:
 at least one transmissive light modulator including a first light modulation signal input, and 
 at least one reflective light modulator including a second light modulation signal input, 
   wherein a ratio of a number of transmissive light modulators to a number of reflective light modulators to is less than 3-to-1.   
     
     
         2 . The liquid crystal display according to  claim 1  wherein the ratio is 1-to-1. 
     
     
         3 . The liquid crystal display according to  claim 1  wherein the reflective light modulator comprises:
 a first electrode, 
 a second electrode, and 
 a liquid crystal material located between the first electrode and the second electrode, 
 
       wherein the liquid crystal material is Vertical Alignment type liquid crystal type. 
     
     
         4 . A display system comprising:
 a liquid crystal display with
 at least one transmissive light modulator including a first light modulation signal input, and 
 at least one reflective light modulator including a second light modulation signal input, 
   wherein the at least one transmissive light modulator and the at least one reflective light modulator are present in the liquid crystal display in a ratio of one-to-one; and
 a circuit, coupled to the first light modulation signal input and the second light modulation signal input, including a circuit input for receiving binary input signals, wherein the circuit implements a first binary-to-voltage conversion function that produces a first light modulation voltage signal that is coupled to the first light modulation signal input and the circuit implements a second binary-to-voltage conversion function that produces the second light modulation voltage signal that is coupled to the second light modulation signal input, 
   wherein the first binary-to-voltage conversion function and the second binary-to-voltage conversion functions do not produce equal voltages for all input binary values.   
     
     
         5 . The display system according to  claim 4  wherein, for a given binary input signal, a voltage produced by the second binary-to-voltage conversion function is substantially equal to one-half of a voltage produced by the first binary-to-voltage conversion function. 
     
     
         6 . The display system according to  claim 4  wherein the circuit comprises:
 a binary subpixel data changer that alters either binary values used to generate the first light modulation voltage signal or binary values used to generate the second light modulation voltage signal and thereby produces a difference between the first binary-to-voltage conversion function and the second binary-to-voltage conversion function. 
 
     
     
         7 . The display system according to  claim 6  wherein the binary subpixel data changer comprises:
 a memory with a look up table. 
 
     
     
         8 . The display system according to  claim 6  wherein the binary subpixel data changer operates substantially according to the following equation:
     F   change   =F   ˜−1   driver,1 ( F   −1   display,+2 (Brightness(BPV)) 
 where
 Brightness(BPV) is an overall response of the liquid crystal display to an input binary pixel value BPV; 
 F ˜−1   driver,1  is an inverse of a voltage as a function of binary function F ˜   driver,1 (BPV) wherein F ˜   driver,1 (BPV) is at least approximately equal to a function F driver,t (BPV) given by:
     F   driver,1 (BPV)= F   −1   display,1 (Brightness(BPV)) 
 
 F −1   display,1  is an inverse of light modulation as a function of input voltage function F display,1  for a first subpixel selected from the group consisting of the first transmissive light modulator subpixel and the second reflective light modulator subpixel, and 
 F −1   display,2  is an inverse of light modulation as a function of input voltage function F display,2  for a second subpixel selected from the group consisting of the first transmissive light modulator subpixel and the second reflective light modulator subpixel. 
 
 
     
     
         9 . The display system according to  claim 8  wherein: 
       
         
           
             
               Brightness 
               ∝ 
               
                 
                   ( 
                   
                     BPV 
                     255 
                   
                   ) 
                 
                 γ 
               
             
           
         
         where gamma is a parameter that controls a nonlinear response of the liquid crystal display. 
       
     
     
         10 . The display system according to  claim 4  wherein the reflective light modulator comprises:
 a first electrode, 
 a second electrode, and 
 a liquid crystal material located between the first electrode and the second electrode, 
 
       wherein the liquid crystal material is Vertical Alignment type liquid crystal type. 
     
     
         11 . A liquid crystal display comprising:
 a 2-D array of subpixels including:   a first set of transmissive color subpixels; and   a second set of reflective subpixels,   wherein each of the transmissive color subpixels and the reflective subpixels is coupled to a separate transistor, and   wherein the reflective subpixels are substantially larger than the transmissive subpixels.   
     
     
         12 . The liquid crystal display according to  claim 11  wherein the reflective subpixels are about two times larger than the transmissive subpixels.