MLX75031 Datasheet, PDF (15/67 Pages) Melexis Microelectronic Systems – Optical Gesture & Proximity Sensing IC

MLX75031
Optical Gesture & Proximity Sensing IC
with Integrated LED Drivers
Datasheet
8. Detailed General Description
8.1. Active Light Channels A & B
The MLX75031 has two separate Active Light channels. Both channels work synchronously & independently.
These channels are able to detect the amplitude/intensity of a reflected signal whilst subtracting the DC
variation of the background light or sunlight illumination.
The LEDs transmit one single light pulse (pulse duration is programmable via TP<2:0>) which is detected by
the channel receiver. The pulse amplitude is sampled and amplified by a S&H stage synchronized with the
LED pulse.
In addition to the LED pulse amplitude programming, the effective trans-impedance can be adjusted in
order to maximize the dynamic range of the system.
The calibration to find the best working point should be calculated and set by means of the µController over
the SPI interface.
8.1.1. Transimpedance Amplifier (TIA)
The transimpedance amplifier converts the photocurrent of the connected photodiode into a voltage signal.
The overall transfer function for the Active Light channels is defined by following formula :
 ^{ADC _ ActiveLight} − ¹  × 3.3 +1.45× GAIN _ BUF
I _pd = ^
65535
2_
0.02× GAIN _ ADJ × GAIN _ BUF × k
• I_pd : the current through the photo diode (in µA)
• ADC_ActiveLight : the decimal value of the Active Light measurement (see Output Data Frame of read-out)
• GAIN_BUF : the gain value selected by the GainBuf register
• GAIN_ADJ : the gain value selected by the SetAL or SetBL register
• k : Factor causing by signal attenuation from TIA. Range from 50% - 90%.
The TIA’s DC-light cancellation circuitry delivers a 16bit value of the received (external) DC light.
REVISION 001 – JANUARY, 2013
39010xxxxx
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