Patent Application
20080078921
A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.”
As shown in
The light sensors could include any device capable of providing a meaningful, detectable output in response to light intensity. Examples of light sensors that could be used with the invention include discrete photosensitive semiconductors, pixilated light sensors (which could be within the plane of and mechanical boundaries of the display), thin film transistor light sensors, and charge coupled devices, etc.
Included in the device 10 is a lighting unit 120 for controlling display brightness, as shown in
The processor 122 generates a pulse width modulated (PWM) signal to an LED driver 126 that powers an array of LEDs 128. The PWM signal is a periodic signal in which the percentage of each cycle in which the PWM signal is asserted determines the brightness of the display 102. For example, if the PWM signal is asserted for only 33% of the cycle, then the display 102 will appear to be outputting only about one-third of its maximum brightness and if the PWM signal is asserted for 100% of the cycle, then the display 102 will appear to be outputting its maximum brightness. While PWM is employed in the present embodiment, it should be understood that many other methods of controlling display brightness could be employed within the scope of the invention. For example, the brightness could be modified by controlling the voltage or the current applied to the lighting unit, or any other method of controlling light intensity of a display.
Also, additional light sensors could be employed to increase redundancy. In such a case, rather than using only one first sensor and only one second sensor, a first sensor array and a second sensor array would be used. The processor could average all of the sensors from and array and could reject anomalous signals. This approach would compensate for individual light sensor failure.
In one prototype embodiment, the following components were used: model no. TPS851 light sensors, available from TAEC Sales Office, 2150 E. Lake Cook Road, Suite #310, Buffalo Grove, Ill. 60089; model no.: PIC12F675 microprocessor, available from Microchip Technology Inc., 2355 West Chandler Blvd., Chandler, Ariz., USA 85224-6199; and model no. FDG6324L switch, available from Fairchild Semiconductor. 1721 Moon Lake Blvd., Suite 105, Hoffman Estates Ill. 60194.
In an embodiment employing a PIC12F675 microprocessor, the threshold about which the microprocessor decides the output brightness depends upon the chip's reference voltage. Since this reference voltage depends on the supply voltage, a steady Vdd is important in maintaining a consistent threshold value. Since the MCLR pin for the microprocessor is not used in this embodiment, it is connected to ground through a 100 Ohm resistor. The resistor is necessary because the MCLR pin is sensitive to Voltage spikes below Vss (which in the prototype embodiment equals ground). Without the resistor to maintain the pin voltage slightly above ground, the microprocessor could latch up. This would cause the output PWM to be 100% regardless of the input from the light sensors.
As shown in
In one method 146 of determining the light intensity, as shown in
Initially, the system sets 148 the brightness state (“B”) to “low” and the pulse width (“PWM”) to 33% (indicating that the asserted pulse width will be 33% of the period of each cycle). A brightness state of “low” indicates either that the output from the display is at its lowest value or that the output is changing in the direction to its lowest value. Similarly, a brightness state of “high” indicates either that the output from the display is at its highest value or that the output is changing in the direction to its highest value. A test 150 determines if both of the sensors (S1 representing the front sensor and S2 representing the back sensor) have been read a predetermined number (“n”) of times. If not, the processor will sample both sensors 154 and store the output from the sensor indicating the greatest ambient light intensity 152. Then the system will return to test 150. If the predetermined number of samples has been read, then the system will calculate the average of the stored sensor readings 156. One way of doing this is to sum each of the stored sensor outputs and divide them by “n.”
The system determines 158 which brightness state it is in. If the current brightness state is “low,” then the system determines 160 if the average result of the stored sensor readings is less than a predetermined “upper” threshold. If the average result is less than the upper threshold, then the system will a predetermined increment (in this embodiment, the increment is 0.27%) to the pulse width output by the processor and will set the brightness state to “high.” 162. If the average result is greater than or equal to the upper threshold, the system will determine 166 if the current pulse width is greater than a predetermined minimum pulse width (in this embodiment, the minimum is 33% of the total cycle time). If the pulse width is at the minimum pulse width, then the system will output 164 its current value for pulse width. If the pulse width is above the minimum, then the system will subtract 168 a predetermined decrement from the pulse width and then output 164 the new current value for pulse width.
Returning to step 158, if the brightness state is not set at “low” (e.g., it is “high”), then the system determines 170 if the average result is greater than a “lower” threshold. If not, then a predetermined decrement is subtracted from the pulse width and the brightness state is set to “low” 172. Otherwise, the system determines if the pulse width is less than a maximum value 174. If not (i.e., the pulse width is currently at its maximum), then the system will output 164 the current value of the pulse width. Otherwise, it will add a predetermined increment to the pulse width 176 and output the pulse width 164. Once the pulse width is output 164, the system repeats the process and returns to step 150. By waiting until the result has gone above a high threshold to begin incrementing output brightness and until the result has gone below a low threshold to begin decrementing brightness, the system adds hysteresis to the brightness control, thereby preventing display brightness jitter as a result of such events as briefly passing under a shadow.
Several brightness transition scenarios are shown in
In one embodiment, a visually smooth transition is used to change display intensity from one brightness level to the next. Multiple auxiliary lighting brightness steps may be employed when transitioning from one final auxiliary lighting level to the next in order to produce a visually smooth transition. For example, in one embodiment, going from a high intensity to a low intensity may involve 100 steps. One embodiment of a display lighting system could employ multiple first and second thresholds and correspondingly multiple final (target) auxiliary lighting levels. Also, the invention can be applied to self-emissive displays and any display that provides its own light without or in conjunction with auxiliary lighting, such as organic light emitting diode (OLED) displays.
In one embodiment, it may be desirable to increase the lighting of the display when the display is in a relatively dark environment and decrease the lighting of the display when the display is in a relatively light environment. This embodiment could be useful with displays such as transflective displays (displays that use ambient light for illumination) and key pads (displays used for user input). In such an embodiment, the lighting unit is driven so that light from the lighting unit has a high intensity value when the maximum value is less than a first intensity threshold and so that light from the lighting unit has a low intensity, less than the low intensity, when the maximum value is greater than a second intensity threshold.
The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.
