A broadband SiGe mixer for 5-GHz WLAN applications with X-band quadrature generation and high image-rejection

We report on the realization of an image-reject receiver that covers the various WLAN bands in Europe, Japan and the US, fabricated using a low-cost, 0.8 μm production-line SiGe-HBT process. A modified Gilbert mixer with a common-base input stage allows for a broadband RF operation from 2.5-6 GHz at a low supply voltage of 3 V. Broadband quadrature generation was achieved by using a fully integrated X-band VCO at 10 GHz in conjunction with a master-slave divider rather than using a polyphase filter or a quadrature VCO. While consuming less chip-area than competing solutions, we achieve an excellent image suppression of 40-45 dB without any post-tuning.