Method and apparatus to control display brightness with ambient light correction
First Claim
Patent Images
1. A visual information display system with ambient light correction comprising:
- a visible light sensor configured to output a sensor current signal in proportion to the level of ambient light;
a dimming control input signal determined by a user to indicate a desired brightness level for one or more light sources, wherein the dimming control input signal is represented by a user adjustable pulse-width-modulation logic signal;
a multiplier circuit configured to generate a brightness control signal based on a mathematical product of the sensor current signal and the dimming control input signal, wherein the multiplier circuit comprises;
a pair of current steering diodes configured to multiply the sensor current signal by the user adjustable pulse-width-modulation logic signal to generate the brightness control signal, wherein anodes of the current steering diodes are coupled to an output of the visible light sensor to receive the sensor current signal;
a network of resistors coupled to cathodes of the current steering diodes and configured to scale the brightness control signal; and
at least one capacitor coupled to the network of resistors and configured as a low pass filter for the brightness control signal; and
a display driver configured to adjust brightness levels of the light sources in response to the brightness control signal.
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Abstract
An ambient light sensor produces a current signal that varies linearly with the level of ambient light. The current signal is multiplied by a user dimming preference to generate a brightness control signal that automatically compensates for ambient light variations in visual information display systems. The multiplying function provides noticeable user dimming control at relatively high ambient light levels.
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Citations
21 Claims
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1. A visual information display system with ambient light correction comprising:
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a visible light sensor configured to output a sensor current signal in proportion to the level of ambient light; a dimming control input signal determined by a user to indicate a desired brightness level for one or more light sources, wherein the dimming control input signal is represented by a user adjustable pulse-width-modulation logic signal; a multiplier circuit configured to generate a brightness control signal based on a mathematical product of the sensor current signal and the dimming control input signal, wherein the multiplier circuit comprises; a pair of current steering diodes configured to multiply the sensor current signal by the user adjustable pulse-width-modulation logic signal to generate the brightness control signal, wherein anodes of the current steering diodes are coupled to an output of the visible light sensor to receive the sensor current signal; a network of resistors coupled to cathodes of the current steering diodes and configured to scale the brightness control signal; and at least one capacitor coupled to the network of resistors and configured as a low pass filter for the brightness control signal; and a display driver configured to adjust brightness levels of the light sources in response to the brightness control signal. - View Dependent Claims (2, 3, 4, 5, 6, 8, 9)
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7. A visual information display system with ambient light correction comprising:
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a visible light sensor configured to output a sensor current signal in proportion to the level of ambient light; a dimming control input signal determined by a user to indicate a desired brightness level for one or more light sources; a multiplier circuit configured to generate a brightness control signal based on a mathematical product of the sensor current signal and the dimming control input signal, wherein the dimming control input signal is provided as a digital word and the multiplier circuit further comprises; a digital-to-analog converter configured to receive the digital word and to output an analog signal representative of the brightness control signal based on a multiplication of the digital word and a reference voltage; an isolation diode with an anode coupled to an output of the visible light sensor to receive the sensor current signal and a cathode coupled to a network of resistors, wherein the network of resistors conducts the sensor current signal to generate the reference voltage for the digital-to-analog converter; and an optional output capacitor configured as a low pass filter for the reference voltage; and a display driver configured to adjust brightness levels of the light sources in response to the brightness control signal.
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10. A method to adjust display brightness over ambient light variations, the method comprising the steps of:
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sensing ambient light with a visible light detector, wherein the visible light detector outputs a sensor current signal that varies linearly with the ambient light level; multiplying the sensor current signal with a user-adjustable dimming control input signal to generate a brightness control signal, wherein the user-adjustable dimming control input signal is a pulse-width-modulation logic signal and the multiplying step further comprises the steps of; steering the sensor current signal toward a network of resistors when the pulse-width-modulation logic signal has a first logic level; and steering the sensor current signal away from the network of resistors when the pulse-width-modulation logic signal has a second logic level, wherein the network of resistors generate the brightness control signal based on a multiplication of the sensor current signal and a duty cycle of the pulse-width- modulation logic signal; and providing the brightness control signal to a display driver to thereby adjust brightness levels of one or more light sources. - View Dependent Claims (11, 12, 13, 14)
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15. A method to adjust display brightness over ambient light variations, the method comprising the steps of:
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sensing ambient light with a visible light detector, wherein the visible light detector outputs a sensor current signal that varies linearly with the ambient light level; multiplying the sensor current signal with a user-adjustable dimming control input signal to generate a brightness control signal, wherein the user-adjustable dimming control input signal is a digital word and the multiplying step further comprises the steps of; providing the digital word to a digital-to-analog converter for conversion to an analog output voltage that is representative of the brightness control signal; and generating a reference voltage for the digital-to-analog converter by driving a resistor network with the sensor current signal from an output of the visible light detector such that the brightness control signal is based on a multiplication of the sensor current signal and a value of the digital word; and providing the brightness control signal to a display driver to thereby adjust brightness levels of one or more light sources.
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16. A visual information display system with ambient light correction comprising:
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means for monitoring ambient light and generating a sensor current signal with an amplitude proportional to the ambient light level; means for multiplying the sensor current signal and a dimming control input signal with a first current steering diode and a second current steering diode to generate a brightness control signal, wherein the dimming control input signal is a pulse-width-modulation logic signal, the first current steering diode conducts the sensor current signal when the pulse-width-modulation logic signal has a first logic level, and the second current steering diode conducts the sensor current signal when the pulse-width-modulation logic signal has a second logic level such that the brightness control signal is based on a multiplication of the sensor current signal and a duty cycle of the pulse-width-modulation logic signal; and means for adjusting display brightness of one or more light sources with the brightness control signal. - View Dependent Claims (17, 18)
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19. A brightness control circuit comprising:
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a visible light sensor configured to generate a sensor current signal indicative of ambient light; a buffer circuit configured to receive a pulse-width-modulation logic signal indicative of a user desired brightness level; a pair of current steering diodes comprising a first diode and a second diode with commonly connected anodes that are coupled to an output of the visible light sensor to receive the sensor current signal, wherein the first diode conducts the sensor current signal when the pulse-width-modulation logic signal has a first logic level and the second diode conducts the sensor current signal when the pulse-width-modulation logic signal has a second logic level; a network of resistors coupled to an output of the buffer circuit and cathodes of the first diode and the second diode, wherein the network of resistors generates a brightness control signal at an output node based on a multiplication of the sensor current signal and a duty cycle of the pulse-width-modulation logic signal; and a display driver configured to receive the brightness control signal and to deliver power to one or more light sources to achieve a brightness level in accordance with the brightness control signal. - View Dependent Claims (20, 21)
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Specification