適用於共電流雙頻帶接收機前端電路之偶次諧波混頻器設計

Abstract

由於吉爾伯混頻器在直接降頻或低中頻接收機的應用中，存在著本地振盪訊號洩漏的問題，這將會導致中頻輸出端產生直流偏差而破壞接收機的特性。因此，在本論文中首先提出一個雙平衡式偶次諧波混頻器，它的動作原理是以吉爾伯混頻器為基礎。此一混頻器的特點是，所需的本地振盪訊號頻率是射頻訊號頻率的一半，故改善了直流偏差的問題。 接著我們將此偶次諧波混頻器應用到接收機中，藉由它的二倍頻特點，我們提出一個應用於802.11a/b/g的全新共電流雙頻帶接收機架構，而這個新的雙頻帶接收機架構僅需一組本地振盪源。在第三章中，我們整合了共電流雙頻帶低雜訊放大器及偶次諧波混頻器來實現共電流雙頻帶接收機前端電路。 以上兩組晶片皆以CMOS 0.18μm的製程實現，除了電路的描述及模擬結果外，實際量測結果也涵括在這篇論文之中。如同一般射頻工程師所可能遇到的困難，量測結果與實驗結果並不完全相符，因此我們也分別對兩者之間的差異以及可能的原因作一些說明和探討。

Since Gilbert mixer has the problem of the LO leakage in the direct conversion or low-IF receiver applications, this will cause the DC offset in the IF output port to degrade the performance of the receiver. In this thesis, we completed a double-balanced sub-harmonic mixer with its design approach based on the classical Gilbert mixer. This mixer with an LO signal operating at half of RF frequency can improve the DC offset in the IF output port. Then we apply this sub-harmonic mixer to the receiver. By employing this sub-harmonic mixer with an LO signal operating at half of RF frequency, we propose a new concurrent dual-band receiver architecture with only one frequency synthesizer for 802.11a/b/g applications in this thesis. We integrate the concurrent dual-band LNA and sub-harmonic mixer to implement the concurrent dual-band receiver front-end in Chapter 3. These two IC have fabricated in a CMOS 0.18μm technology. Except the circuit descriptions and simulated results, this thesis includes the measured results of the circuits mentioned earlier. As all designers may be confronted with, the measurement results fall short of simulation results. Thus, we also discuss the differences between simulations and measurements and the possible reasons.