Design and Analysis of Even-Harmonic Mixers for Direct Conversion Receivers

• Main Authors: Yen-Chia Chen, 陳彥嘉
• Other Authors: 陳怡然
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/73746258823213062120

碩士 === 國立臺灣大學 === 電子工程學研究所 === 95 === Wireless Communication System has been highly developed for quite a long time. Although many circuits are operating in digital format nowadays, analog and radio frequency circuits are still important blocks in the system. Because digital circuits take signal from radio-frequency IC, digital circuits are highly affected by the surrounding circuits which are so-called the front-end architecture. In receiver, antenna receives signal from the air. Signal was amplified by the LNA which is the first stage of the front-end. After LNA, signal needs to be down-converted to base-band which is done by mixer. Mixer designers concentrate on linearity rather than conversion gain. Power consumption is also one of the most important specifications in mixer design. In order to avoid DC offset which is caused by LO self-mixing, even-harmonic topology is developed in recent years. That is, use second order harmonic frequency term of local-oscillator to accomplish the frequency mixing. Although even harmonic topology efficiently reduces DC offset issue, it also has its own design difficulties such as higher power consumption and higher supply voltage. High power is needed to enhance conversion gain. Since CMOS technology is constantly developed in order to reduce supply voltage, circuits design skills need to be developed with process improvement to decrease energy dissipation. In this thesis, a novel technique to reduce power dissipation and supply voltage is presented. This design focuses on linearity and power consumption of the circuit, and maintains the other characteristics in reasonable values. Cascoding topology is used to achieve this goal in stead of cascading. Four different circuits are designed, including two broad-band mixers, one narrow-band mixer and one passive mixer. Improved Broad-band mixer achieves flat conversion gain with fairly small power consumption. Narrow-band mixer also has very good characteristics and consumes relatively low power. Passive one solves the problems of the conventional anti-parallel diodes in terms of LO and RF signal combination issue. Loss of the mixer is only 3 dB power which is also a prominent characteristic.