Ka-Band單晶毫米波功率放大器及新式可控制增益雙向放大器之分析與設計

Abstract

本篇論文的第一部份描述運用在汽車防撞雷達系統中的Ka頻段功率放大器電路之分析與設計。為符合防撞雷達所需的線性度及高效率，選擇採用二級的功率放大器，第一級使用class A架構供應足夠的功率增益，同時設計第二級為Class AB架構以提高RF-to-DC訊號比，並利用匹配電路壓制訊號經過電路所產生的二階及三階諧波以提升線性度。PHEMT半導體材料因為擁有較高的崩潰電壓及較低的通道摻雜，適合用來設計高功率與高頻的射頻電路，故為了使電路能運用在Ka頻段中，選擇利用WIN 0.15-um GaAs PHEMT製程設計這兩個電路，量測結果上，在操作中心頻率32.4GHz時，功率放大器有P-1dB為2dBm，Pout@P-1dB為12.4dBm，PAE@P-1dB為19.7%。 論文的第二部分實現以兩個反射式放大器及一個90度branch-line電路為架構的新式2.4GHz可控制增益雙向放大器，其可有效提高電路的隔離度，並降低雜訊指數，提昇訊號品質，不過因為此類放大器原理與振盪器相似，故在設計過程中必須非常小心訊號的振盪。反射式放大器為單端輸入、輸出的元件，將輸入的訊號放大並從同一端點輸出；而Branch-Line電路功能為將輸入端訊號分成二個相位差為90度、且功率相同的輸出訊號，並且在隔離埠(Isolation Port)的功率為零；藉由上述元件的特性，雙向放大器可獲得放大的輸出訊號，增益大小與一個反射式放大器相同；並加上可變電容電路，讓此電路依照需求調整增益，且能藉著此電容穩定電路的振盪情形。因為傳統90度Branch-Line電路在2.4GHz時面積太大，不適合在CMOS裡實現，所以選擇放在FR4板上採用外加電容的方法將縮小其面積。反射式放大器的增益為13.6dBm，P1dB為-5dBm，雜訊指數為14.3dB；而雙向放大器的回損S11皆在-10dB以下，增益變化從7.5dB到16dB，雜訊指數變化為4.1到5.4，可藉可變電容值調整，不過當增益值愈大時，則回損S11相對也愈大。

This thesis is divided into two parts. The first part describes the analysis and design of a Ka-Band power amplifier applied to the automotive collision avoidance radar system. In order to acquire the adequate linearity and efficiency of the system requirements, the architecture with two stages is adopted to design the power amplifier. The first stage utilizes class-A type to supply sufficient power gain. The second stage improves RF-to-DC signal ratio by class-AB type. By this way, the linearity of this circuit can also be improved. The semiconductor material of PHEMT is adequate to design the RF circuits with the characteristics of high power level and high operating frequency because it possesses the higher breakdown voltage and the lower doping channel. So as to operate the circuits at Ka-band, we select the semiconductor process of WIN 0.15-um GaAs PHEMT to design the circuits. At the central frequency of 32.4GHz, the measured results reveal that the fabricated power amplifier has the P-1dB of 2dBm、Pout of 12.4dBm, and PAE of 19.7% at P-1dB point. The second section of this thesis proposes and demonstrates a novel architecture of 2.4GHz bi-directional amplifier. The approach improves effectively the isolation and noise figure of the circuit to ameliorate the quality of output signal. The framework includes two reflection-type amplifiers and a 90 degree branch-line circuit. The designed process must pay attention to the oscillation condition because its principles are similar to that of an oscillator. Meanwhile, the ability of bi-direction could be realized in accordance with the characteristic of branch-line circuit. The bi-directional amplifier with this architecture can obtain the gain which is same as that of a reflection-type amplifier. Also, a variable capacitance is arranged to steady the condition of oscillation and adjust the gain according to the circuit’s requires. And the conventional branch-line circuit must be realized by means of transmission lines with the quarter wavelength. This length is 16.7mm at the operating frequency of 2.4GHz. This approach is inappropriate for CMOS IC. Therefore, this 90 degree branch-line circuit is realized on a FR4 board and utilizes a new method to reduce the area. So, this IC only embraces these two critical reflection-type amplifiers. And the expected specifications of this reflection-type amplifier are as follows: power gain 13.6dBm, P1dB -5dBm，the noise figure 14.3dB. Furthermore, the return loss S11 of this bi-directional amplifier is below -10dB across overall utilized bandwidth. The gain can alter from 7.5dB to 16dB and the noise figure varies from 4.1 to 5.4.