Liquid crystal display device with automatic constrast control

Claim 1

A liquid crystal display apparatus comprising: a liquid crystal display unit having liquid crystal cell means for use in detection of display contrast, the liquid crystal cell means comprising a pair of liquid crystal cells, one held in an OFF state and the other held in an ON state, so as to monitor the display contrast; a photosensor unit for sensing an intensity of light transmitted through the liquid crystal cell means and for converting the sensed intensity into a corresponding signal; a contrast detecting unit receptive of the corresponding signal for producing an electric signal indicative of the display contrast a voltage control unit receptive of the electric signal for producing an output signal effective to control a drive voltage applied to the liquid crystal display unit, the voltage control unit including a peak-hold circuit for holding a peak of the electric signal to produce the output signal effective to control the drive voltage; and a stabilized power supply unit receptive of the output signal from the voltage control unit for supplying a stabilized drive voltage to the liquid crystal display unit so as to automatically control the display contrast of the liquid crystal display unit.