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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]

Operating conditions

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

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Light sources consists of ac noise frequencies. For example a flourescent light consists of about 100Hz ac noise frequency. A low pass filter is required to be added in the circuit parallel with the load resistor to decrease the ripple.

Figure 23: Electronic configuration for APDS-9003[1]

As shown in figure 23, 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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