具有改良匹配電感設計之SAW濾波器進階模組之研發

Abstract

本篇論文主要以載波聚合(Carrier Aggregation)的方式設計應用於長期演進技術 4G、5G頻段上的多工器。聲波材料(LiTaO3)的機電耦合系數限制，設計SAW Extractor以及六工器，同時參考Qorvo在2020年發表的產品規格，利用微波頻段的濾波器結合SAW濾波器，實現UHB+MHB的頻段結合應用。 第一部份的SAW Extractor設計概念是將帶通濾波器(BPF)、帶阻濾波器(BSF)，整合成一個Extractor，此Extractor包含8個基於mBVD的共振器，特色是運用並聯電感與並聯的SAW共振器產生共振，使其在低頻時為高通濾波器，高頻時為電容，與商業產品相比，所設計的SAW Extractor可以滿足0.7 ~ 2.7GHz頻率範圍內的產品規格，驗證時以YX 42°切角之鉭酸鋰作為驗證之壓電材料，量測結果與模擬結果的驗證(實驗結果:S_21通帶為-3.5dB，止帶為-35dB，S_31通帶為-2dB，止帶為-20dB)。 第二部分雙工器的設計則結合WIFI 6E頻段(5.925~7.125GHz)的微波濾波器與SAW濾波器，特色是運用一顆簡單匹配電感以及運用頻率響應的方式，設計出一個可使用於(2.4GHz+WIFI 6E)的RF元件，量測結果與模擬結果的驗證(實驗結果:S_21通帶為-3.8dB，止帶為-20dB，S_31通帶為-2dB，止帶為-40dB)。 第三部分本文基於IHP SAW的機電偶合係數下，提出一個等效電路架構萃取電感的方法，設計市售SAW六工器的匹配網路，同時也進行濾波器性能最佳化。結果看出最佳化完後的電感值與初始設計值只差了0.02%，同時也討論多工器一顆電感下的設計極限，在頻帶間距不超過4倍以上，均可以達到良好的匹配網路設計。

This study focuses on the design of multiplexers for LTE 4G and 5G bands using carrier aggregation. It includes the design of the SAW Extractor and Band2-66-30 hexaplexers with fixed. Electromechanical coupling coefficient on the same acoustic wave material, LiTaO_3 and a UHB+MHB diplexer consisting of microwave filter and SAW filters, with reference to Qorvo's product specifications released in 2020 for various applications. In the first part of SAW Extractor design, the concept involves integrating a bandpass filter (BPF) and a bandstop filter (BSF) consisting of eight SAW resonators. This configuration exhibits resonance of parallel inductors and capacitors, thereby acting as a high-pass filter at low frequencies and a capacitor at high frequencies. Under lossless assumption, it meets specified requirements of existing commercial produect in 0.7 - 2.7GHz. Realized in piezoelectric material LiTaO_3 cut at YX 42° angle, the experimental results are in good agreement with the design, showing that S_21 is -3.5dB in passband, -37dB in stopband; while S_31 is -2dB in passband, and -20dB in stopband. The second part focuses on combining a SAW filter for WiFi 2.4 GHz and a microwave filter for WIFI 6E band (5.925~7.125GHz), aiming to create a RF diplexer in both 2.4GHz and WIFI 6E bands. The design approach involves a simple matching inductor design and a frequency response method. The measurement results and simulation results are verified well, with the following performance: S_21 is -3.8dB in passband, -20dB in stopband; while S_31 is -2dB in passband, and -40dB in stopband. In the third part, the study proposes an equivalent circuit structure based on the electromechanical coupling coefficient of IHP SAW to extract the inductance, leading to the matching network for a commercial SAW hexaplexer design. After numerical optimization, the initial design proposed by the present approach differs from the optimized inductance only 0.02%. In addition, the limitation of the single-inductor topology as a matching network is discussed, which performs adequately if the bandwidth of the multiplexer is less than four times.