Optical touch sensor devices and systems

A touch sensor system comprising:

• a sensing area having a periphery;
• a plurality of light sources and a plurality of analog optical detectors arranged about the periphery of the sensing area,
• wherein each of the plurality of analog optical detectors comprises:
• a respective photodiode;
• a respective first bipolar transistor having a first base, a first collector, and a first emitter, wherein the first bipolar transistor is coupled to the photodiode in a current amplifier configuration that generates an amplified current output as a function of a photodiode current, the photodiode being coupled to the first base and reversed biased, the first bipolar transistor arranged to amplify the photodiode current by a current gain factor to generate the amplified current output in the first collector, wherein a modulated enable input signal drives the first collector of the first bipolar transistor through a first resistance;
• and
• a respective second bipolar transistor having a second base, a second collector, and a second emitter, and the second base of the second bipolar transistor is connected to the first collector of the first bipolar transistor and the first resistance,
• wherein the second collector of the second bipolar transistor is coupled to a voltage source, and the second emitter of the second bipolar transistor is connected to an output of the optical detector, and
• wherein the first resistance is connected in series between the second base of the second bipolar transistor and a detector input that receives the enable input signal;
• wherein the first emitter of the first bipolar transistor is coupled to ground;
• and
• wherein, the modulated enable input signal is modulated between:
• a first signal voltage level that forward biases the first collector and enables generation of the amplified current output by the first bipolar transistor, the second emitter of the second bipolar transistor following a voltage across the first resistance generated by the amplified current output;
• and a second signal voltage level at which a collector-to-emitter junction and a base-to-emitter junction of the second bipolar transistor are both reverse biased and generation of the amplified current output by the first bipolar transistor is disabled,
• wherein the outputs of the plurality of analog optical detectors are collectively connected to an analog databus.