System and method for converting ambient light energy into a digitized electrical output signal for controlling display and keypad illumination on a battery powered system
View Patent ↗A system and method of ambient light detection with digitized output. A light sensitive device is coupled to electronic circuitry for receiving an output of the light sensitive device corresponding to a level of ambient light. The electronic circuitry compares the output to a threshold level. The threshold level corresponds to a desired level of light. The electronic circuitry for provides an output signal indicative of said desired level of light.
1. A method of illuminating a display on a battery powered system, comprising:
converting ambient light energy into an electrical signal with a Gallium Arsenide Phosphate (GaAsP) photodiode;
accessing said electrical signal from said GaAsP photodiode via a node on an integrated circuit device;
amplifying said electrical signal from said GaAsP photodiode with an amplifier in said integrated circuit device;
filtering said electrical signal from said GaAsP photodiode with a low pass filter in said integrated circuit device, wherein said filtering prevents a flicker effect on said signal from flickering ambient light conditions;
comparing said amplified, filtered electrical signal to a threshold level with a comparator in said integrated circuit device, said threshold level corresponding to a pre-determined level of ambient light;
generating an output signal from said comparator indicating whether said ambient light is greater than or less than said threshold level;
driving and buffering said output signal at a driver stage in said integrated circuit device, wherein said driving and buffering generates a signal compatible with voltage and drive levels required for digital logic;
direct coupling said output signal with a processor, wherein said processor comprises digital logic circuitry;
activating an illumination source if said ambient light is less than said threshold level, wherein said activation is performed by said processor.
2. The method of claim 1 further comprising:
selecting a gain level from a plurality of gain levels to amplify said electrical signal.
3. The method of claim 2 wherein said selecting comprises: utilizing a digital input to select said gain level.
4. The method of claim 1 further comprising:
selecting a low power quiescent mode subsequent to said generating.
5. The method of claim 1 , wherein said illumination source comprises a backlight LED for illumination of said display.
6. The method of claim 1 , wherein said battery powered system further comprises a keypad and a backlight LED array for illumination of said keypad, wherein said activation of said illumination source backlights said keypad.
7. A battery powered computer system comprising:
a processor:
an ambient light detection device comprising a Gallium Arsenide Phosphate (GaAsP) photodiode disposed to receive ambient light falling upon said computer system;
an integrated circuit device comprising
a node for accessing a current corresponding to light energy of said GaAsP photodiode;
a resistor for adjusting a voltage to light energy relationship of said current;
an amplifier for amplifying said current;
a low pass filter for filtering said current to prevent a flicker effect on said current due to said light received at said GaAsP photodiode;
a comparator for comparing a voltage of said current after said amplifying and said filtering to a threshold voltage and for generating an output signal, wherein said output signal indicates if said light energy received by said GaAsP photodiode is greater than or less than a desired ambient light level; and
a driver stage for driving and buffering said output signal to make said output signal compatible with voltage and drive levels of said processor, wherein said processor is direct coupled with said output signal after said driving and said buffering; and
an illumination source controlled by said processor, wherein if said output signal indicates that said light energy received by said GaAsP photodiode is less than a desired ambient light level, said illumination source is activated.
8. The computer system of claim 7 wherein said ambient light detection device is contained in a semiconductor package.
9. The computer system of claim 7 wherein said electronic circuitry further comprises:
a selectable gain control for determining amplification of said electrical signal.
10. The computer system of claim 9 wherein said selectable gain control is selected via digital input.
11. The computer system of claim 7 wherein said electronic circuitry further comprises:
a selectable low power quiescent mode.
12. The battery powered computer system of claim 7 further comprising a display, wherein said activation of said illumination source backlights said display.
13. The batter powered computer system of claim 7 wherein said display is a liquid crystal display.
14. The battery powered computer system of claim 7 further comprising a keypad, wherein said activation of said illumination source backlights said keypad.
15. The battery powered computer system of claim 7 wherein said battery powered computer system is a mobile telephone.
16. The battery powered computer system of claim 7 wherein said battery powered computer system is a personal digital assistant.