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• Electronic Signs and Signals

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Figure 1: Application of sensor in smartphones 2

As shown in figure 1, the APDS-9003 sensors can be used as Ambient Light Detection sensor. They are responsible for dimming the light with respect to the surroundings light. They are also responsible to black out the screen during a call. This helps to save the power of the device and increase the life of the screen and power source.

Relative Spectral Response vs Wavelength

Figure 12: Relative Spectral Response Vs wavelength[1]

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Figure 2: Typical application circuit[1]

Operating conditions

ParameterSymbolMinMaxUnit
Storage/Operating TemperatureTs/Ta-4085°C
Maximum rating Supply VoltageVcc06V
Operating Supply VoltageVcc2.45.5V

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So if we check the figure and the sensitivity the change in wavelength changes the sensitivity response. The change in Lux also changes the current by 1.2. Typically, the white light is used as the source which consists of 3Volts input signal with 100 illuminance. However the output depends on the load ressistor connected with the sensor. As the increase in the illuminance effects the output signal it is better to avoid unwanted lights except the source light.

Interface Electronic circuits

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Figure 3: Electronic configuration for APDS-9003[1]

As shown in figure 3, The 3V Vcc is supplied to the sensor in pin 1 and pins 2 to 5 are not connected. Pin 6 is the output pin. When a light source strikes the sensor it produces photo current. The current through load resistor creates the analog voltage output. The capacitor in parallel with the RL filters the noise and the filtered signal is converted to digital format in our electronic devices using A/D converter or a microcontroller.

 

Materials and Manufacturing Technologies

 
Thursday, April 24, 2014 10:17 AM
Photoresistors

Photo resistors are classified into two types according to the materials used to build them. They are intrinsic and extrinsic. In the intrinsic photo resistor electrons in the valence band are excited to the conduction band due to the photons that fall in the device, as a result more free current carrying electrons in the material are produced and therefore less resistance.

However extrinsic photo resistors are built of the materials doped with impurities known as dopants. These dopants reduce the energy gap by creating a new energy band above the existing valance band. As a result the electrons need less energy to make transition to the conduction band. This makes the device sensitive to different wavelengths of light.

In contrast to the different type of photo sensor, Both types of sensors use silicon and germanium, one with impurity and next without. Both types will exhibit decrease in resistance when illuminated. Thus, Increase in the light intensity, decrease in the resistance.

References

  1. Anchor
    [1]
    [1]
    APDS-9003, Avago Technologies datasheet
    URL: http://www.avagotech.com/docs/AV01-0238EN [Online], Last Accessed: 10.4.2014
  2. Anchor
    [2]
    [2]
    Mobile phones- much more than just telephones, Avago Technologies
    URL: http://www.sekorm.com/Ectm/19789 [Online], Last Accessed: 10.4.2014

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