應用於WLAN之PHEMT單壓操作低雜訊放大器與改進閃爍雜訊之直接降頻式混頻器

Abstract

本論文針對WLAN前端電路的雜訊議題來研究，分成設計PHEMT低雜訊放大器與改善閃爍雜訊之直接降頻器兩個部份。 LNA提出一個可以自偏壓的架構，即使使用空乏型PHEMT製程元件，整個電路仍只需要一個正極偏壓；因此，本論文實作了兩個LNA，其中2.4GHz的單頻帶LNA達到1.43dB低雜訊指數與15.7dB的增益，還有2.4GHz/5GHz雙頻帶LNA，兩個頻帶的雜訊指數都約在3.4dB，證實此架構可應用於雙頻帶。 於降頻器的部份，已有文獻討論出電路雜訊與LO開關級的偏壓電流和電路的寄生電容有關，以此觀點出發，實作了三種具有改善閃爍雜訊的電路，分別為靜態電流分流、動態電流分流、靜態電流分流結合串聯共振電感；如何進行準確的低頻雜訊量測是個挑戰，本論文會論述我們做了哪些嘗試來解決外在雜訊的干擾；0.13um CMOS動態電流分流降頻器量到12.8dB雜訊指數與4MHz轉角頻率；而PHEMT降頻器有量到靜態電流分流的效果，電路的雜訊指數為11.4dB，轉角頻率從80MHz壓低至40MHz。

Noise is an important issue for the WLAN front-end applications, especially in the direct-conversion system. This thesis focuses on the two topics of PHEMT LNAs and low flicker-noise mixer. The first is to design a single biasing PHEMT LNAs by our proposed self-bias technique. Under a single supply of 3 V, the 2.4 GHz LNA achieves the noise figure of 1.43 dB and the gain of 15.7 dB. The other LNA operating at the dual band of 2.4 GHz/5 GHz has noise figure about 3.4dB at these two bands. The current consumption of them are 10 mA and 12.6 mA, respectively. The next studies the flicker noise of mixer, which is closely related to the biasing current of the switch core, and the circuit parasitic capacitance. We approach this issue in the three different methods, including the static curent bleeding, dynamic current bleeding and static curent bleeding with two series resonant inductors. Moreover, the technique of low-frequency noise measurement will be discussed in detail. It is because the surrounding noise will degrade the measurement quality seriously. How to make a clean environment is another challenge in the flicker-noise research. From the measured results, the dynamic current bleeding mixer implemented in 0.13um CMOS process achieves 12.8 dB noise figure and 4 MHz corner frequency, and the 0.15m□ PHEMT mixer with static-current injection has an obvious improvement in lowering the corner frequency (from 80 MHz to 40 MHz).