低損耗且具高頻帶邊緣選擇特性之小型低溫共燒陶瓷帶通濾波器

Abstract

本論文旨在提出一個於低頻頻帶邊緣具有高選擇性之T型的二階帶通濾波器，對於低溫共燒陶瓷濾波器來說，導體損耗比介質損耗影響來的大很多。因此想要操作頻帶內損耗小，設計高Q值的電感是非常重要的。為了達到高Q值，我們提出了一個新的T型架構並且在三維佈線實現上使用垂直的via來取代平面電感。T型帶通濾波器的電路架構簡化步驟在文中也有詳細的分析。值得一提的是，之前LTCC的文獻都有使用側面電極。然而，現在手機越做越小，裡面的元件也都被要求越來越小。因此，除了縮小元件體積，只使用底面電極也可以減少焊接的面積，且相對於有使用側面電極的架構，其設計困難度較高。而本篇論文是第一篇只使用底面電極的設計。 本研究使用低溫共燒陶瓷技術，設計一操作頻率2.4-2.5GHz的帶通濾波器。此濾波器在1.8-1.9GHz GSM頻帶有不錯的衰減，特別是在離操作頻帶很接近的2.11-2.17GHz IMT頻帶具有大於30dB的衰減，這些頻帶都是對手機頻帶有很大影響的。此濾波器只使用底面電極且尺寸為1.6mm x 0.8mm x 0.508mm。此外，在論文後段也以三階交錯耦合濾波器架構同樣設計在2.4-2.5GHz，在2.17GHz有大於25dB的衰減，此設計在1.8-1.9GHz的衰減較T型濾波器好，但輸入損耗也較T型濾波器大，此濾波器也只使用底面電極且尺寸為1.6mm x 0.8mm x 0.528mm。此二種設計實際量測實作後的濾波器，其量測結果比起模擬結果都偏低頻，但都和模擬結果具有相同特性。

In this thesis, a second-order T-type bandpass filter with sharp lower band-edge selectivity is presented. For an LTCC filter, the conductor loss is often more dominant than the dielectric loss in the RF range. Therefore, the design of high-Q inductors is very important as it has significant influence on the passband insertion loss. Here, in order to achieve high-Q, we proposed a new T-type structure, and used vertical via pairs to replace planar inductors. The simplified procedure of T-type bandpass filter is analyzed in detail. Note that, all the published literatures used side electrode. Nowadays, the space of cell phone is limited, and each component is requested much smaller. In addition to miniaturized size, using bottom electrode can also reduce the area of welding. This thesis is the first work using only bottom electrode which decreases PCB using space and is more difficult in design. A bandpass filter of 2.4-2.5 GHz was designed and measured based on Low Temperature Co-fired Ceramic (LTCC) technology. The filter shows good attenuation at the 1.8-1.9 GHz GSM and WCDMA bands, especially at 2.11-2.17 GHz IMT-band which is important for mobile bands of cellular phones. This filter uses only bottom electrode and the filter’s overall size is 1.6mmx0.8mmx0.508mm. In the next part, a third-order cross-coupled filter structure applied for the same 2.4-2.5GHz is designed. The attenuation at 2.11-2.17GHz of the filter is better than 25dB. Compared to T-type filter, this filter has better attenuation at the 1.8-1.9 GHz, but has bigger inband insertion loss. This filter also uses only bottom electrode and the filter’s overall size is 1.6mmx0.8mmx0.528mm. Compared with the full-wave electromagenetic designed responses, the measured results slightly shifts toward the lower frequency. Nevertheless, the correlation of the simulated and the measured results agrees very well.