Ambient Light Sensor with 358pW / cm^2 equivalent noise floor for behind screen operation

This paper describes the design and performance of an ultra-high sensitivity ambient light sensor (ALS) for use behind an organic light emitting diode (OLED) display. A low-capacitance photodiode is biased at ground using a custom analog readout. Typically, the display brightness is controlled using PWM (pulse width modulation) and photo charge integration is performed when the display is off and the pixel is held in reset when the display is on. This enables the rejection of photons produced by the display and measured values are solely that of the ambient illuminance.