Development of a digital lock-in amplifier for photoconductivity measure in photorefractive materials

• Grant number: 15/18217-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2015
• End date: October 31, 2016
• Field of knowledge: Engineering - Electrical Engineering - Electrical, Magnetic and Electronic Measurements, Instrumentation
• Principal Investigator: Rangel Arthur
• Grantee: Guilherme Paulino
• Host Institution: Faculdade de Tecnologia (FT). Universidade Estadual de Campinas (UNICAMP). Limeira , SP, Brazil

Abstract

This research project aims to study and to develop a digital equipment to measure photoconductivity that will serve mainly to characterize photosensitive crystals. To study photosensitive materials, for example, the Bi12TO20, which usually generate very low currents in the order of tens of picoamperes (pA), is necessary obtain an instrument able to measure this scale and with low noise. In February 2015 was the master's dissertation defense of the student William Roberto de Araujo, which endorsed the development and testing of this equipment based on excitation performed using a disk with LEDs, but used analog devices, filters with operational amplifiers and external synchronization. The equipment built could generate important results, but it is susceptible to noise and is based on a number of devices that require timing synchronism. From this, will be proposed for this Scientific Initiation the digitalization and signal processing using FPGA (Field Programmable Gate Array). One of the challenges of the proposal is to implement an Amplifier "Lock-in", which aims to identify and filter signals of interest, eliminating spurious frequency components. A digital Amplifier "Lock-in" prevents the use of precision analog devices that are expensive and are less susceptible to temperature variations and offsets. In addition, the objective is change later the excitation source of the present meter to white light to eliminate unwanted behaviors of the crystals current response due to wavelength ranges of LEDs. Is aimed with the new digital photoconductivity meter that new crystals can be characterized and new characteristics can be found.