SIGE HBT DUAL-CONVERSION WEAVER-HARTLEY DOWNCONVERTERS WITH HIGH IMAGE REJECTION

Abstract

GHz dual-band Weaver-Hartley dual-conversion downconverters are demonstrated using 0.35-m SiGe heterojunction bipolar transistor (HBT) technology with/without a correlated local oscillator (LO) generator. In the flrst implementation, the correlated LO generator consists of a divide-by-two frequency divider, a frequency doubler and a single-sideband upconverter and thus LO1 (= 2:5£LO2) signal is generated. As a result, the downconverter with the correlated LO signals has image-rejection ratios of more than 39dB for the flrst/second image signals (IRR1/IRR2) of the dual-conversion system at both 2.4/5.7-GHz modes while the downconverter without the correlated LO generators has a 6-dB higher conversion gain and IRR1/IRR2 of more than 44dB with the same dc power consumption (excluding the LO generator). On the other hand, a 10-GHz Weaver- Hartley downconverter is demonstrated with a resonant LC load at the flrst-stage mixer to improve the conversion gain at high frequencies. The downconverter achieves a conversion gain of 8dB with IRR1/IRR2 better than 43/40dB.