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Optimization MAX44007 ambient light sensor, designed to improve the performance of black glass

In Electronic Infomation Category: O | on May 03,2011

Abstract: The black glass will change according to ambient light sensor in the light spectrum, which is an ambient light sensor facing the design challenges. Especially the black glass-reinforced components of the spectrum in the infrared, but not this part of the spectrum the human eye. This application note describes several calibration / compensation to optical sensors with different light conditions in the lumen readings corrected. This article discusses how to use the MAX44007 high-level model light sensor to adjust its visible light, IR channel response. MAX44007 can optimize the use of sensors register under glass in black performance.

Introduction

MAX44007 ambient light sensor provides advanced operating modes, to optimize the sensor performance under glass in black.

Now, most smart phones, tablet PCs, laptops and LT1077 datasheet and TV has a black glass LCD screen as a framework that makes the end product looks exquisite, beautiful. Traditional design, the location of the ambient light sensor to provide a clear circular window or gap. The new products, the light sensor window or gap is almost opaque black ink coverage, seamless color of its surroundings. The manufacturers reason is simple: the deeper the color, the more user attention is not easy to disperse, will look more professional, more refined look!

Unfortunately, the dark ink coverage ambient light sensor, it will result in design complexity in two ways. First, attenuation of ambient light to dark ink, thereby reducing the amount of light received by the sensor. Second, the ink has also changed the light spectrum. See from the spectral characteristics of ink, nearly all of the incident light through the infrared, and LT1077 price and visible light is attenuated to its original light intensity of 3% to 5%. Therefore, the infrared content of ambient light is greatly magnified. As the actual chemical properties of the dark ink with the vendor will vary, so that the optical signal transmission (infrared light or ambient light) are further complicated.

Black glass for calibration and LT1077 suppliers and compensation

Accurately match the CIE curve of the human eye is very difficult. For this reason, most of the high ambient light sensor (eg MAX9635) with a calibration / compensation mechanisms, under different light sources used to correct the number of lumens. Such an amendment through a combination of both on-chip photodiode implemented effectively combined to provide accurate readings of light intensity to eliminate the influence of different lighting conditions. Black glass beneath the light sensor in the spectral change significantly the need for further adjustment of calibration parameters.

Need to pay special attention to light on the impact of black glass beneath the sensor, its calibration correction. If the light in the infrared component is greater, such as sunlight and incandescent light, in particular, need to be corrected. White LED (WLED) and fluorescent lighting, the necessary adjustments small.

MAX44007 has advanced mode, can be used to adjust the visible and IR signals for the response.

Glass bottom sensors used to optimize the performance of register The following is the MAX44007

register, the device also provides data on the register table.


One-time pre-set, power set

Follow the steps below pre-set time, usually at power settings.

1. Read four registers the contents of each register: 0x09-0x0C.

Storage variables: namely Adv1, Adv2, VisibleGain and IRGain.

2. Will complement these variables is saved as a new variable: namely Adv1C, Adv2C, VisibleGainC and IRGainC. For example, IRGainC =! IRGain;

If IRGain = 1010 0110, the IRGainC = 0101 1001.

3. 0x0D write 10000001 to register to enter the advanced mode (the ADV set 1).

4. Will Adv1C, Adv2C, VisibleGainC and IRGainC were written to register 0x09-0x0C.

Example, write to the register 0x0C 01,011,001, 10,100,110 of its original value.

Note: The following read register 0x0C (after the write operation), is still read back 01,011,001, because the IC in the high-level register data to the internal automatic bit before flipping.

Reserved IRGainC value for future use.

5. Necessary for the door when the register is limited to setting an appropriate delay 0x07.

6. Set the INTE = 1 (register 0x01), enable the interrupt.

Into the normal operating mode

The following steps to enter the normal measurement mode.

7. Read registers 0x03 and 0x04, get 12 lumens readings.

The value saved as ComboLux.

8. 0000 0000 to register 0x0C is written into the temporary measurement mode.

9. Wait for at least 1.6s (2x 800ms).

If necessary, contact Maxim shorten this time.

10. Read registers 0x03 and 0x04, get 12 lumens readings.

The value saved as ApproxLux.

11. To register 0x0C is written IRGainC, withdraw the provisional measurement mode.

12. Calculation: ActualLux = ApproxLux - IRFactor (ApproxLux - ComboLux)

AcutalLux the actual ambient light readings.

ApproxLux = ComboLux, similar to fluorescent lamps and WLED lamps.

ApproxLux> ComboLux, usually incandescent, and sunlight. For calculating the appropriate

IRFactor, please contact Maxim application support, and provide the glass samples. Can be obtained directly from the laboratory test data.

13. According to the above calculation ActualLux, set the backlight intensity accordingly.

14. Will ComboLux as a reference (the devices normal operating mode), set the upper limit of the corresponding lumen (register 0x05) and the minimum lumen (register 0x06).

15. Executive INTS bit (Register 0x00) read empty, clear all interrupt (if previously set).

16. Waiting for hardware interrupt.

Process takes the longest time.

17. A hardware interrupt, the read register 0x00, confirmed INTS = 1.

If INTS = 1, then go to step 7 above.

Otherwise, if INTS = 0, checking other hardware interrupt source, return to step 16.

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