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Unformatted text preview: Highly Integrated and Tunable RF Front-Ends for Reconfigurable Multi-Band Transceivers Hooman Darabi Broadcom Corporation, Irvine CA Abstract ⎯ Architectural and circuit techniques to integrate the RF front-end passive components, namely the SAW filters and duplexers that are traditionally implemented off chip, are presented. Intended for software defined radios, tunable high-Q filters allow the integration of highly reconfigurable transceiver front-ends that are robust to in-band and out-of-band blockers. Furthermore, duplexer techniques based on electrical balance concept are introduced to enable highly integrated and programmable radios for full duplex applications such as 3/4G transceivers. I. INTRODUCTION A software-defined radio (SDR) [1-3] is a highly programmable device that is reconfigured through software to operate over a wide range of carrier frequencies and channel bandwidths. One of the most popular applications of the SDR is 3G cell phones, which allow as many as 16 bands in 3 modes of operation, GSM, EDGE and WCDMA/HSPA. The first SDR architecture was proposed by Mitola , where the RF and analog processing are reduced to only a pair of data converters as shown in Fig. 1(a), hence providing the maximum flexibility and programmability through the digital processing block. This idealistic approach however, suffers from a fundamental limitation; that is, the poor tolerance of such a radio to the interferers. For instance, shown in Fig. 2, in a GSM receiver, a weak desirable signal is specified to be accompanied by very large in and out of band blockers that due to the lack of any filtering in the SDR of Fig. 1(a), would demand an impractical dynamic range of about 100dB on the ADC. According to the survey published in , this leads to an unacceptable power dissipation of 2kW estimated for the ADC! Thus, a more practical receiver architecture shown in Fig. 1(b) is adopted in most SDR’s today , where by means of down-conversion a considerable portion of analog and digital signal processing is performed at a conveniently lower intermediate frequency (IF) . The difference from the other traditional radios is the added programmability in almost everything, including filter bandwidth, or ADC sample rate to allow several modes of operation, as well as extended RF bandwidth and PLL range to support multiple bands. Even though this architecture solves the in-band blocker problem through IF filtering , still the out-of-band blockers remain a challenge. In the case of GSM for example, the 0dBm blocker can heavily compress the RX front-end, and thus desensitize it. Therefore, an additional front-end filter is needed to suppress the blocker adequately (Fig. 1(b)). Due to the very high Q nature of such a filter, it is typically implemented externally, which adds to the cost and size of the reference design. Moreover, since the filter bandwidth or center frequency are inevitably not programmable, for every band or mode of operation a dedicated input and its...
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This note was uploaded on 04/02/2011 for the course ECE 264 taught by Professor Song during the Spring '11 term at UCSB.
- Spring '11