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Design Of DFB Laser Driver Based On FPGA

Posted on:2014-01-12Degree:MasterType:Thesis
Country:ChinaCandidate:X Y WangFull Text:PDF
GTID:2248330395997128Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
Distributed Feed back laser (DFB) is a typical wavelength tunable laser, and it isoften used as a light source in the gas concentration detection. The biggest feature ofDFB laser is monochromatic, and it has a high side mode rejection ratio (SMSR,>40-50dB). In the detection of gas concentration, compared with the normal testingmethods, wavelength modulation method is to add the sine signal superposedtriangular wave to the laser and use the two harmonic amplitude to characterize thegas concentration, and then we detect the two harmonic of sine signal, which canmake the detection sensitivity higher2-3magnitude than the direct absorption. Inorder to match the wavelength of DFB laser with the absorption peak of gas, itswavelength must be tune precisely. So the study on DFB laser driver has practicalvalue.Firstly, the paper describes the principle of DFB laser, and researches the basicidea of the laser driver. It Focuses on the tunable diode laser absorption spectroscopy(TDLAS) and the wavelength modulation method, and then proposes the overallscheme of the driver circuit based on the wavelength modulation method.Secondly, ATmega16microcontroller is used as the core to finish the hardwaredesign of the drive circuit. Because the sine wave and the triangular wave need to addto finish the laser’s modulation and scanning, so the adder circuit is designed. Thevoltage-controlled constant current source circuit is based on the OP37chip, and it isdesigned to get a constant current of the laser driver. At the same time, the drivercircuit further includes key circuit, display and communication circuit.Then, the software part is focused on Direct Digital frequency Synthesis (DDS)which is designed by Field Programmable Gate Array (FPGA). The simulation of theDDS is achieved by Quartus II software, and the output frequency of DDS can beadjusted by controlling the frequency word, and the corresponding waveform can bechanged by the stored data in the ROM. Finally, as the experimental aspect of the paper, DDS system uses VHDLlanguage and Quartus II software download the design in the FPGA chipEP2C8Q208C8, and then we can generate a20kHz sinusoidal signal and20Hztriangular signal. The constant current generated by the voltage-controlled constantcurrent source is in the range0-100mA. At last, Using the simulated load to carry outexperiments, the results showed the constant current generated by the driver is in therange of20-100mA.
Keywords/Search Tags:FPGA, DFB, laser driver, DDS, ATmega16, wavelength modulation
PDF Full Text Request
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