數位訊號處理器為基礎之雷射訊號辨識與電路設計技術

Abstract

本論文以數位訊號處理器發展出雷射測距儀的偵測系統，當雷射測距儀發射調製頻率的訊號到目標物的表面時，雷射光束來回飛行產生一個極短的時間延遲，如果可以透過對此極短的時間差作測量，就可以計算目標物的距離，精密系統控制實驗室（PSCL）針對此困難度發展出降階式相位法，將極短時間差的測量轉換成相位差的測量，並且將雷射訊號的負載頻率降到10KHz以利訊號的測量，本論文針對訊號量測建置出硬體電路與以數位訊號處理器為基礎之感測裝置，並將調製頻率的訊號轉換成數位訊號，利用數位訊號處理器的捕獲來抓取訊號位元數的改變，再利用時間差計算相位差，實驗結果量測的解析度為0.4到2公分。

In this thesis we develop the digital signal processing subsystem for a reflecting laser range finder. The laser range finder shines a frequency modulated laser beam at the target surface. The distance traveled by the laser beam creates a short time delay in the nanosecond range. One can calculate the distance to the target if he has the mean to measure this very short time difference. To target this difficulty, the precision system control laboratory developed a double frequency shifting (DFS) technology to transform the time delay measurement into a phase difference measurement and to shift the carrier frequency down to a slower 10 KHz range for easy measurement. This thesis builds the hardware circuit and the DSP based phase difference sensing device for the measurement. We convert the frequency modulated signal into digital on-off signal and use the capture feature of the DSP to capture the bit change event and to count the resultant time delay for phase measurement. Experimental results confirm 0.4 to 2 cm measurement resolution from the device hardware.