Ambient light detector, detector array and method

#The present application concerns an ambient light detector. The application also refers to an ambient light detector, a detector array and a method of forming an ambient light sensor.

#An Ambient Light Sensor (ALS) is an electronic device that measures intensity of an ambient illumination and outputs an electrical signal proportional to the level of illumination. The output may then be used to control the strength or colour temperature of a lighting device. An ALS may include a photodiode array and a current amplifier.

#Dark current is the relatively small electric current that flows through photosensitive devices, such as photodiodes, even when no photons are entering the device. The dark current consists of charge carriers generated in the detector when the detector is not illuminated by incoming light. It is a temperature depending characteristics of semiconductors. The dark current can be increased by heating of the photodiodes and correspondingly reduced when the diode is cooled down.

#Further aspects and different examples are further disclosed in detail with the accompanying Figures, in which:

#FIG. 1 illustrates an exemplary embodiment of a dark current compensation circuit;

#FIG. 2 shows an embodiment of an ambient light sensor in accordance with some aspects of the proposed principle;

#An ambient light sensor is an electronic device that measures the intensity of ambient illumination. It outputs an electrical signal in some elation to the illumination, for example directly proportional to the illumination. However, due to thermal movement and different ambient temperatures, the photodiode used for ambient light measurement provides a small current, even when the photodiode of the sensor itself is not illuminated. This is called dark current. To achieve a dark current cancellation a second photodiode is often used. FIG. 1 illustrates the principle. A cancellation 1 comprises the sensor photodiode 11 and a dark current photodiode 12. The dark current photodiode is shielded such that no measured light can reach the opening of diode 12. In a combiner 15, the dark current of diode 12 is subtracted from the photodiode 11. The result is amplified in amplifier 14 and provided at output 16.

#The total response of the exposed photodiode 11 comprises the generated photo current induced by the incident ambient light and the (mostly thermally) generated dark current. The dark current diode 12 only provides the dark current. The cancellation results in an improvement of the sensor sensitivity particular at low illumination levels.

#To achieve good results, both photodiode and dark current diode should be similar and arranged close to each other. However, light impinging on a photodiode structure at low angles of incidence or scattered light may reach the dark current diode and create a crosstalk between adjacent structures.