This technique is illustrated in the schematic of Figure 1. It comes in a variety of combinations, 7,8,9 but essentially relies on the same principle - the RF signal is first amplified in a frequency selective low noise stage, then translated to a lower intermediate frequency (IF) with significant amplification and additional filtering, and finally down-converted to baseband with either a phase discriminator or straight mixer, depending on the modulation format. It has been used extensively and is well understood. The superheterodyne or heterodyne receiver is the most widely used reception technique and finds numerous applications from personal communication devices to radio and TV tuners. After a brief description of alternative and well-established receiver architectures, this article presents the direct conversion reception technique and highlights some of the system level issues associated with DCR. Overcoming some of the problems associated with the traditional superheterodyne and being more prone to integration, DCR has nevertheless an array of inherent challenges. The present article refers to several recent publications 5,6 which provide a thorough survey and insight, and display renewed interest in direct conversion receivers. Besides, it favors multi-mode, multi-standard applications and thereby constitutes another step towards software radio. Over the last decade or so, the drive of the wireless market and enabling monolithic integration technology have triggered research activities on direct conversion receivers, which integrated with the remaining analog and digital sections of the transceiver, have the potential to reach the "one-chip radio" goal. Another paper by Tucker in 1954 4 reports the various single down-conversion receivers published at the time and clarifies the difference between the homodyne (sometimes referred to as coherent detector) and the synchrodyne receivers - the homodyne receiver obtains the LO directly (from the transmitter, for example), whereas the synchrodyne receiver synchronizes a free-running LO to the incoming carrier. Tucker, 3 which first coined the term synchrodyne, for a receiver which was designed as a precision demodulator for measurement equipment rather than a radio. Additional developments in 1947 led to the publication of an article by D.G. Colebrook in 1924, 2 and the term homodyne was applied. Very much like its well established superheterodyne receiver counterpart, first introduced in 1918 by Armstrong, 1 the origins of the direct conversion receiver (DCR) date back to the first half of last century when a single down-conversion receiver was first described by F.M.
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