Conditioning Stage of a QADA Receiver for a Large Range IR Positioning System

Optical positioning systems in the infrared or visible spectrum find application in the tracking of people or mobile vehicles in indoor spaces. A line of research proposes the use of LED emitters, acting as tags to be positioned, and quadrant receivers (QADA, Quadrant Photodiode Angular Diversity Aperture) located at known positions in the infrastructure. These systems can operate at a measurement rate that can reach some MHz at relatively low cost. Apart from the challenge of high-speed processing, they must also deal with low and changing signal-to-noise ratios (measurements at short and long distances, with different transmitter-receiver angle of view, etc.). This paper deals with the design of the analog conditioning stage of a QADA receiver taking into account that it must operate in a linear area with large dynamic signal margins and provide three outputs, one sum signal and two differential signals, that must be amplified with identical gain, as the performance of the triangulation algorithms used in positioning depends on this. Each signal has a transimpedance amplifier with continuous and low-frequency backlight cancellation. Furthermore, an automatic gain control with a large dynamic range is applied to the sum signal and the gain derived over time is used to manage two variable gain amplifiers for the other two differential signals. Some results are presented that show the performance of the system.