Susie Maestre

user Electronics Engineer

city Innovuze Solutions Inc.

  • ADPD105 Photometric Front End

  • Created: Oct 25, 2016

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In science, photometry is the measurement of light in terms of its perceived brightness to the human eye. Instruments used in photometry are called photometers. These devices function by collecting light through some kind of input optics, passing it through a spectral modifying filter and then measuring the light with a photosensitive detector. The filter is carefully trimmed to modify the detector response so that it matches the International Commission on Illumination (CIE) photopic or scotopic function. The detector converts the incoming light energy into an electrical signal, which is then amplified and displayed. This reference design features ADPD105 photometric front end with an integrated 14-bit analog-to-digital converter (ADC) and a 20-bit burst accumulator that works well with flexible light emitting diode (LED) drivers.

This circuit is an evaluation board for ADPD105 photometric front end. This provides users with simple means of connecting optics to the ADPD105 photometric front end to evaluate the ADPD105 in a number of different applications, from vital signs monitoring to industrial sensing. The USB port powers the circuit and the on-board voltage regulators provide voltage supplies for the ADPD105, ADuCM360, and FTDI Chip FT232. There are on-board regulators that provide 3.3V and 4.3V LED supplies, as well as a selectable option to add an external LED supply. The evaluation board provides an LED and photodiode for a finger Photoplethysmography (PPG) measurement that is useful for a quick functionality check of the evaluation system. The evaluation board includes the ADPD103_ADPD105 OpenMarket WaveTool Graphical User Interface (GUI) that provides users with low level and high-level configurability, real time frequency and time domain analysis, and User Datagram Protocol (UDP) transfer capability so the evaluation board can easily interface to the user development system.

Photometric front end is useful in a wide variety of applications especially in medical electronics. It is specifically useful in wearable health monitors, fitness monitors, clinical measurements, industrial monitoring and background light measurements.



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