非反射式雜訊抑制之平衡式饋入帶通濾波器設計

Abstract

在高速電路發展的過程中，以差動形式建立高雜訊抗性、高動態範圍的通訊系統為一常見的手法，射頻前端模組或作為所有通訊系統對外進行資料傳輸之不可或缺的重要電路。本論文致力於平衡式饋入之帶通濾波器的新式設計，其最大的特色為針對雜訊抑制的手法採用非反射式的設計，此為過去相關的研究未曾著墨的方式，以系統觀點視之，這樣的方式能夠避免反射的雜訊漫流於系統中，以輻射或其他形式的干擾影響元件的正常運作。 本論文先提出了兩種四埠平衡式帶通濾波器的設計。此二者皆以傳統三階四分之波長帶通濾波器改良，第一種電路利用共模虛開路的特性，將中間級設計為高阻抗電路，搭配前後二級設計阻抗匹配，致使雜訊能夠在一定的頻寬內被吸收。第二種電路，則在共模上引入衰減器的特性控制雜訊抑制的深度，能夠使雜訊在所有頻率範圍內控制在一定的深度以下，達到非常寬頻的雜訊抑制響應。 接著，為改善分散式元件面積過大的問題，本論文提出第三種設計，以集總元件實踐平衡式帶通濾波器的設計，與第一種設計相同，其電路前後級在共模下皆可針對一特定頻率進行匹配設計，唯在第三種設計中，中間級的高阻抗特性並無頻寬限制，因此在縮小化的同時亦達到寬頻抑制以及雜訊吸收的特性。 最後，為展示全頻段無反射的雜訊抑制概念，本論文提出一種基於耦合傳輸線所設計的平衡式帶通濾波器，藉由電阻調整耦合線之輸入阻抗，再以外展級調整其阻抗匹配於系統阻抗，便可完成一全頻段雜訊無反射之平衡式帶通濾波器。

Under the trend of high-speed network development, it is a common approach to establish a communication system in the form of differential architecture due to its high immunity to noise and high dynamic range. This dissertation is devoted to exhibit new concepts of balanced bandpass filter (BBPF) designs. Non-reflective common-mode (CM) noise-rejecting feature (Absorptive or Reflectionless) is the most prominent point, which has not been linked in the related researches in the past. From the aspect of system performance, it is possible to prevent the reflected noise power from roaming around in the system, affecting the normal operation of other components by radiation or other forms of interference. In the beginning, this dissertation proposes two kinds of four-port BBPF design. Both of the designs are based on the conventional branch-line BPF. For the first design, CM noise is rejected by the intermediate stage due to the virtual open boundary at the operating frequency, while the input and output stage are designed as matching circuits to the system impedance at the same frequency. Therefore, the CM noise would be absorbed into the loading resistors instead of reflected within a certain bandwidth. In the second design, the concept of π-type attenuator is introduced into the CM circuit, so that the noise rejection can be controlled below a specified level and the filter exhibits a very broadband noise suppression response. Next, in order to improve the excessively large area taken by the distributed elements, this dissertation reports the third BBPF design that implemented by lumped elements. Similar to the first design, the input and output stages are the matching circuit at the operating frequency band. However, in the third filter design, the high input impedance seeing into the intermediate stage has no bandwidth limitation, which results an all-stop characteristic of CM response. In a short word, the third design not only keeps the merits of the previous two filter designs, but also has the advantage of size reduction. Additionally, in order to demonstrate the concept of reflectionless noise rejection, a BBPF based on the terminated coupled line pair is proposed in this dissertation as the fourth filter design. For CM, the input impedance is adjusted to the system impedance by terminated coupled line pair at the middle stage and the external cells with resistor-loading branch lines on the both sides of coupled line pair. Thus, the proposed fourth BBPF design with the reflectionless noise rejection is complete.