FPGA Design to an Variable Optical Attenuator Control Circuit

• Main Authors: Shu-wen Pan, 盤舒文
• Other Authors: Wan-De Weng
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/19448246104460776276

碩士 === 雲林科技大學 === 通訊工程研究所碩士班 === 97 === The dissertation uses the FPGA (Field Programmable Gate Array) to replace the 8051 (single-chip microprocessor) in the VOA (Variable Optical Attenuator) applications. In the whole system, the analog circuit includes the O/E (optical to electro) conversion, the ADC (Analog to Digital Converter), the DAC (Digital to Analog Converter), the VOA driver, and rectifier circuits, and the digital circuits are designed on FPGA development board: the Max II Starter Kit and use the ALTERA Quartus Ⅱ 7.0 software to design, simulation, and burn. The digital circuits is divided into the input/compare circuit, the fine tune circuit, the default output value select circuit, the output buffer circuit, and the system clock generator circuit. In the system, the sampling rate is 512 kHz. When only use the fine tune circuit, the attenuation rates are changed from 3 dB to 10 dB and from 10 dB to 3 dB the transition times are 2.25 ms and 2.4 ms, respectively. When the default output value select circuit is used, the attenuation rates are changed from 3 dB to 10 dB and from 10 dB to 3 dB the transition times are 0.65 ms and 0.95 ms, respectively. The default output value select circuit can effectively reduce the transition times. When the default output value select circuit is used, too, the attenuation rates are changed from 0 dB to 19.87 dB（attenuation rate is 97）and 19.87 dB and 0 dB, the transition times are 0.5 ms and 0.76 ms, respectively, when un-use and use the default output value select circuit, respectively. The transition times are similar to the attenuation rates are changed from 3 dB to 10 dB and from 10 dB to 3 dB. Therefore, the transition times are independent on the changing of the attenuation rates when use the default output value select circuit.