Temperature compensated color LCD projector

Abstract

In a projection display device based on one or more (twisted nematic) LCDs (4), simple temperature compensation is possible by optimizing the d.DELTAn value (n) at the maximal operating temperature. The associated transmission/voltage characteristics at different temperatures then extend substantially parallel so that it is possible to compensate for temperature changes by means of a simple voltage compensation.

We claim:  
     
       1. A projection display device comprising at least one liquid crystal display device in a light path for a light beam having a central wavelength λ, said display device having a layer of liquid crystalline material of a thickness d, and of a difference in index Δn between two supporting plates provided with electrodes which define at least one pixel, via which electrodes a voltage of a value y can be applied across the pixel, characterized in that in at least one of the extreme transmission states the product d.Δn of the thickness d of the layer of liquid crystalline material and the difference in refractive index Δn is chosen to be such that d.Δn/λ at the  a maximum temperature of use is 0.45-0.50   0 . 76 - 0 . 85 μm, the device being also provided with means for correcting the value of ansaid applied voltage in dependence on thesaid temperature. 
     
     
       2. A device as claimed in claim  1 , characterized in that the electrodes define a matrix of pixels arranged in rows and columns, in which the column electrodes are driven by means of corrected or uncorrected data voltages when a row of pixels is being selectively driven. 
     
     
       3. A device as claimed in claim  1 , characterized in that the liquid crystal display device is present between mutually perpendicularly crossed polarizers and is light-transmissive in an extreme state. 
     
     
       4. A device as claimed in claim  1 , characterized in that the maximal temperature of use of the liquid crystalline material is 80° C. 
     
     
       5. A device as claimed in claim  1 , characterized in that the product  d.Δn at room temperature (20° C.) is between 0.50 and 0.65 μm. 
     
     
       6. A device as claimed in claim  1 , characterized in that a correction value for the voltages is determined by means of temperature measurement in the liquid crystal display device, and in that a measured temperature difference is converted into a correction signal. 
     
     
       7. A device as claimed in claim  1 , characterized in that a correction value for the voltages are determined by mean of light intensity measurement after the light has passed through the liquid crystal display device and in that a measured light intensity difference is converted into a correction signal. 
     
     
       8. A liquid crystal display device for use in a device as claimed in claim  6 , characterized in that the liquid crystal display device also comprises a thermocouple, a temperature sensor or a temperature-sensitive resistor. 
     
     
       9. A liquid crystal display device for use in a device as claimed in claim  7 , characterized in that the liquid crystal display device is provided with an optical sensor and a pixel which is always light-transmissive. 
     
     
       10. A device as claimed in claim  2 , characterized in that the liquid crystal display device is present between mutually perpendicularly crossed polarizers and is light-transmissive in extreme state. 
     
     
       11. A device as claimed claim  3 , characterized in that the  a maximal temperature of use of the liquid crystalline material is 80° C. 
     
     
       12. A device as claimed in claim  4 , characterized in that the product d.Δn at room temperature (20° C.) is between 0.50 and 0.65 μm. 
     
     
       13. A device as claimed in claim  3 , characterized in that a correction value for the voltages is determined by means of a temperature measurement in the liquid crystal device, and in that a measured temperature difference is converted into a correction signal. 
     
     
       14. A device as claimed in claim  3 , characterized in that a correction value for the voltages are determined by means of a light intensity measurement after the light has passed through the liquid crystal display device and in that a measured light intensity difference is converted into a correction signal. 
     
     
       15. A projection display device comprising at least one liquid crystal display device in a light path for a light beam having a central wavelength λ, said display device having a layer of liquid crystalline material between two supporting plates provided with electrodes which define at least one pixel, via which electrodes a voltage can be applied across the pixel, characterized in that in at least one of extreme transmission states the product d.Δn of the thickness d of the layer of liquid crystalline material and the difference in refraction index Δn in relation to an intended maximum temperature of use in chosen to be such that ( d.Δn )/ λ at the intended maximum temperature of use in between  0 . 76  and  0 . 85 .    
     
     
       16. A device as claimed in claim  1 , characterized in that the liquid crystal display device is present between mutually perpendicularly crossed polarizers and is light- transmissive in an extreme state.    
     
     
       17. A device as claimed in claim  1 , characterized in that maximal temperature of use of the liquid crystalline material is  80 ° C.  
     
     
       18. A device as claimed in claim  1 , characterized in that the product d.Δn at room temperature (   20 ° C. )  is between  0 . 50  and  0 . 65  μm.    
     
     
       19. A projection display device comprising at least one liquid crystal display device in a light path for a light beam having a central wavelength λ, said display device having a layer of liquid crystalline material of a layer thickness d and a difference in refractive index Δn between two supporting plates provided with electrodes which define at least one pixel, via which electrodes a voltage can be applied across the pixel, characterized in that d.Δn is chosen to be such that, when cooling the display device from a maximum operating temperature to ambient temperature (   20 ° C. )  d.Δnλ/ has a value which passes a value  (   0 . 87   )  corresponding to a first Gooch  &  Tarry maximum.    
     
     
       20. A projection device as claimed in claim  3  characterized in that the device is provided with means for correcting the applied voltages in dependence on the temperature.