Browsing by Author "Liao, Hua-Yu"

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Large Improvement in Image Rejection of Double-Quadrature Dual-Conversion Low-IF Architectures
(2010-07-01)
Syu, Jin-Siang
;
Meng, Chin-Chun
;
Teng, Ya-Hui
;
Liao, Hua-Yu
;
電機工程學系
The reasons for a degradation of image-rejection performance in double-quadrature-double-quadrature and single-quadrature-double-quadrature dual-conversion low-IF downconverters are fully discussed in this paper. Polyphase filters (PPFs) are inserted at proper positions to minimize the effects of device/signal mismatches, and thus improve the image rejection without calibration. Both a 0.35-mu m SiGe heterojunction bipolar transistor 5.2-GHz double-quadrature-double-quadrature downconverter with an RF PPF and a 0.18-mu m CMOS 2.2/4.8-GHz single-quadrature-double-quadrature downconverter with a switched-band low-noise amplifier (LNA) and a narrowband inter-stage PPF are demonstrated. Compared with our previous work, the 5.2-GHz downconverter achieves a 15-dB improvement in image-rejection ratio (IRR) of the first image signal (IRRR(1)) even without a pre-selection filter or LNA. Additionally, the dual-band downconverter has a 25-dB improvement in IRR of the second image signal (IRRR(2)), which nearly reaches the theoretical limit of a four-stage PPF covering 20-40 MHz.