Photodiode operable in photoconductive mode and photovoltaic mode

摘要

A body-mountable device equipped with a light sensor is disclosed. The light sensor includes a photodiode that operates in either a photoconductive mode or a photovoltaic mode depending on whether the photodiode is reverse biased. A group of switches are arranged to selectively couple the photodiode to first and second voltage sources to configure the photodiode to operate in either mode. A controller selects a mode of operation of the photodiode and controls the switches to cause the photodiode to respond to incident light while operating in the selected mode. The controller then obtains a measurement from the photodiode indicative of the intensity of light received during an exposure interval. The light sensor can thus include a single photodiode and yet be used to alternately obtain measurements based on the photoconductive response of the photodiode or based on the photovoltaic response of the photodiode.

主权项

1. A device comprising:
a photodiode having a light-sensitive area, an anode, and a cathode, wherein the photodiode operates in a photoconductive mode when reverse biased, in which the photodiode generates an internal photocurrent directed from the cathode to the anode in response to light incident on the light-sensitive area, and operates in a photovoltaic mode when not reverse biased, in which the photodiode develops a voltage between the cathode and the anode in response to light incident on the light-sensitive area; a first voltage source; a second voltage source; a sampling capacitor coupled to an output node; a plurality of switches, including:
a first switch coupled between the anode of the photodiode and the first voltage source;a second switch coupled between the cathode of the photodiode and the first voltage source;a third switch coupled between the anode of the photodiode and the sampling capacitor;a fourth switch coupled between the cathode of the photodiode and the sampling capacitor; anda fifth switch coupled between the second voltage source and either the anode or the cathode of the photodiode; and a controller configured to operate the plurality of switches and to obtain voltage measurements of the sampling capacitor, through the output node, so as to alternately: (i) configure the photodiode to operate in the photoconductive mode during a first exposure interval, and obtain, through the output node, a voltage measurement indicative of an amount of current drained through the photodiode during the first exposure interval; and (ii) configure the photodiode to operate in the photovoltaic mode during a second exposure interval, and obtain, through the output node, a voltage measurement indicative of a voltage developed across the photodiode during the second exposure interval.