《trade off in cmos mixer design》.pdfVIP

Chapter 27 TRADE-OFFS IN CMOS MIXER DESIGN Ganesh Kathiresan and Chris Toumazou Circuits and Systems Group, Department of Electrical Electronics Engineering, Imperial College of Science Technology and Medicine 27.1. Introduction Mixers are a very important block in the RF front-end, as they perform the crucial task of frequency conversion. When used in a transmitter, mixers con- vert baseband signals to a higher frequency for transmission. This process is called upconversion. When used in receivers, mixers convert a received signal from a high frequency to lower frequencies. This process is called downconver- sion. Most modern communication systems operate in the 1–2 GHz range [1]. The most widely used communication systems in Europe are GSM, which oper- ates in the 900 MHz band, and DCS 1800, which operates at 1.8 GHz. Bluetooth devices, that arejust starting to appear in the market, operate at around 2.5 GHz. The RF front-end receiver has to convert the signals it receives from 1–2 GHz down to baseband for demodulation and further processing. The exact frequen- cies which the downconversion mixer operates at, and the performance required of it, are strongly dictated by the receiver architecture employed. Most wire- less transceivers use the heterodyne or the dual IF superheterodyne receiver architecture. The design of a mixer depends strongly on the receiver in which it is going to be used. Although upconversion and downconversion mixers are conceptu- ally similar, their design involves various different trade-offs that are unique to either upconversion or downconversion mixers, helping to optimize the mixer for its intended role. This chapter deals with particularly the case of down- conversion mixers, primarily because a downconversion mixer, being used in the RF receive path, has to deal with