直接類比同調合成法綜頻器高純淨度輸出暨快速頻率轉換時間之實踐

Abstract

本論文研究闡述綜頻器之各種頻率合成方式，在頻率步進，切換速度，相位雜訊，突波位準等規格中論述各項優缺點。 一般常見頻率合成方式是採用鎖相迴路設計，規格會在頻率轉換時間及輸出波形純淨度妥協，且輸出訊號常伴隨著相位誤差。 為了達成低相位雜訊、低輸出突波、及快速頻率轉換速度，無相位誤差，我們在體積上作出讓步，採用直接類比合成法去實現綜頻器。 利用相位雜訊極低之石英振盪器，高速除頻低相位雜訊IC，快速開關及高階濾波電路，達成快速頻率轉換時間<1us，大頻寬500MHz輸出，低相位雜訊，高輸出功率，突波位準<55dBc，諧波位準<55dBc等規格。 為了減少頻率步進(frequency step)，及採用直接類比同調合成法所造成體積過大之缺點，本論文利用之電路疊代除頻濾波開關組合(combinations of filters , switches, and dividers)來實現綜頻器，除了縮小體積之優點，亦可以降低日後維修之困難度。

This article analyzes the frequencies synthesis techniques of synthesizers. The strength and shortcoming of major properties, such as frequency step, frequency switching speed, phase noise and spurious level are be discussed . The conventional synthesis technique of PLL compromise the short frequency switching time for the purity of output waveform(such as phase noise, spurious, phase error). In order to achieve output waveform with low phase noise , and low spurious level and fast frequency switching speed, we compromise the volume and utilize the direct analog coherent synthesis method to implement the synthesizer. By utilizing the extreme low phase noise crystal oscillator, and high speed frequency with very low phase noise divider IC , high speed switch, and high order filter circuit, we implement specs such as fast frequency switching time (under 1us), low phase noise, high output power and low spurious level (under 55dBc), low harmonics level(under 55dBc). In order to prevent the shortcomings of large volume caused by direct analog coherent synthesis and reduce the frequency step, the synthesis utilize iterated identical stages circuit designed with combinations of filters , switches, and dividers realize the synthesizer. We can lower the volume and reduce the difficulty in maintenance.