從實測觀點研製低相位雜訊壓控振盪器

Abstract

摘要 本論文利用已知的Leeson 振盪器相位雜訊模型，藉由實際量測元件的特性來設計低相位雜訊的振盪器。討論的內容包含了共振電路的品質因素、電晶體的低頻雜訊及雜訊因子。在品質因素的討論上利用多層陶瓷元件（MLCC）去設計共振電路，在考慮了元件本身的非理想性後我們便可以得到最佳化的品質因素設計，並且提供一個設計流程能夠快速地得到最佳的電感電容的組合。在電晶體雜訊與相位雜訊的討論上，將實際量測數顆電晶體的低頻雜訊，除了擷取其雜訊參數外並設計成振盪器，藉由到最低雜訊的電晶體所設計的振盪器其相位雜訊可低達 -126dBc/Hz offset 100kHz。在以多層陶瓷元件所製造的振盪器中其相位雜訊算是十分優異的。在雜訊因子的討論裡我們成功利用帶拒濾波器阻斷了二階諧波對振盪器相位雜訊的影響，在模擬時可以降低振盪器相位雜訊約14dB，但受限於實際的元件特性，在實作上仍可以有效降低4dB的相位雜訊。在電路的品質因素及電晶體都已經無法加強時，我們所利用的帶拒濾波器仍可以再降低振盪器的相位雜訊。

ABSTRACT Leeson model is adopted in this thesis and actual characteristic of each element to design low phase noise oscillators. The quality factor of the tank, low frequency noise of the transistor and noise factor of oscillators are discussed in the contents. Firstly, the non-ideal of tank part implemented by MLCC is taken account to calculate the quality factor, and the best value of capacitors and inductors can be obtained quickly from one design flow. Secondly, the low frequency noises of three transistors were measured and their noise parameters were extracted. The transistor with lowest phase noise was chosen to design one oscillator. Its phase noise is as low as –126dBc/Hz at 100KHz offset. This result is outstanding for general MLCC oscillators. Finally, the notch filter is used to reduce noise factor of the oscillator then phase noise will be reduced about 4dB. Therefore, notch filter can be adopted even when the quality factor and noise feature cannot be improved. In brief, we can successfully implement low phase noise oscillators after understanding three above variables of Lesson model.