Patent ID: 7755595

Claim:
A backlight brightness control system for a visual display comprising: a light sensor configured to detect ambient light and to output a signal indicative of the ambient light level; and an electronic circuit coupled to the output of the light sensor and configured to generate a brightness control signal that increases backlight intensity of the visual display with increasing ambient light levels for a first range of ambient light levels and decreases the backlight intensity of the visual display with increasing ambient light levels for a second range of ambient light levels, wherein the first range of ambient light levels is lower than the second range of ambient light levels, wherein the electronic circuit further comprises: a summing circuit that combines a first input with a second input to generate the brightness control signal, wherein a first signal is provided to the first input and the first signal increases linearly with increasing ambient light levels for the first range of ambient light levels and is approximately constant for the second range of ambient light levels; a linear amplifier configured to output a second signal proportional to a difference between the output of the light sensor and a threshold signal corresponding to a lower limit of the second range of ambient light levels; and a comparator configured to compare the output of the light sensor with the threshold signal, wherein the second signal is selectively coupled to the second input of the summing circuit when the output of the light sensor is greater than the threshold signal.