Automatic brightness control apparatus
First Claim
1. Apparatus for receiving voltage from a power supply and for producing a periodic electrical output signal whose average value is proportional to the ambient light level and independent of fluctuations in the power supply voltage, comprising:
- a photosensor circuit for producing an electrical signal proportional to the ambient light level and substantially independent of the power supply voltage;
a ramp oscillator circuit for producing a periodic electrical signal having a ramp waveform whose amplitude is proportional to the power supply voltage; and
an output circuit for comparing the photosensor signal to the ramp signal and producing a periodic output signal whose duty cycle is the portion of time the photosensor signal exceeds the ramp signal.
3 Assignments
0 Petitions
Accused Products
Abstract
Automatic brightness control apparatus for providing real time control of the brightness of various types of displays while also providing ambient light compensation is disclosed which includes a photodiode for providing a current proportional to the ambient light level. Amplifiers, together with a load, change the photodiode current to a control voltage indicating the level of ambient light. The control voltage is provided as a reference input to a voltage comparator. The other input to the voltage comparator is the output of a free running ramp oscillator. The pulse width modulated logic signal comprising the output of the voltage comparator is provided as the input for an output driver whose pulse stream output is used to control the brightness of the designated display. The duty cycle of the pulse stream output varies with the ambient light level. Several logic gates are added to the free running ramp oscillator to provide synchronization capability and assure that the ramp output waveform of the ramp oscillator will always begin with an incoming synch pulse. The automatic brightness control apparatus is packaged as a monolithic integrated circuit on a single silicon chip which is housed in a clear plastic 8 pin DIP.
111 Citations
5 Claims
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1. Apparatus for receiving voltage from a power supply and for producing a periodic electrical output signal whose average value is proportional to the ambient light level and independent of fluctuations in the power supply voltage, comprising:
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a photosensor circuit for producing an electrical signal proportional to the ambient light level and substantially independent of the power supply voltage; a ramp oscillator circuit for producing a periodic electrical signal having a ramp waveform whose amplitude is proportional to the power supply voltage; and an output circuit for comparing the photosensor signal to the ramp signal and producing a periodic output signal whose duty cycle is the portion of time the photosensor signal exceeds the ramp signal. - View Dependent Claims (2, 3, 4)
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5. Apparatus for controlling the brightness of a light-emitting display having a plurality of display elements which are sequentially time multiplexed at a certain frequency, comprising:
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means for driving each display element with a periodic electrical signal; means for controlling the duty cycle of the periodic electrical signal to control the brightness of each display element; and means for synchronizing the frequency of the periodic signal driving each said display element to a multiple of the frequency at which the display elements are sequentially time multiplexed.
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Specification