Direct-conversion radio transceivers for digital communications

Abstract

Direct-conversion is an alternative wireless receiver architecture to the well-established superheterodyne, particularly for highly integrated, low-power terminals. Its fundamental advantage is that the received signal is amplified and filtered at baseband rather than at some high intermediate frequency. This means lower current drain in the amplifiers and active filters and a simpler task of image-rejection. There is considerable interest to use it in digital cellular telephones and miniature radio messaging systems. This paper briefly covers case studies in the use of direct-conversion receivers and transmitters and summarizes some of the key problems in their implementations. Solutions to these problems arise not only from more appropriate circuit design but also from exploiting system characteristics, such as the modulation format in the system. Baseband digital signal processing must be coupled to the analog front-end to make direct-conversion transceivers a practical reality.

Frequency-selective MEMS for miniaturized low-power communication devices

“…The design procedure for HF micromechanical filters is virtually identical to that for the previous MF filters, differing only in the specific equations used [33]. Electromechanical analogies are again utilized to design this filter, the bandwidth is again dictated by (6), and again, quarter-wavelength coupling beams and low-velocity coupling are utilized to achieve small-percent bandwidths accurately. For clamped-clamped beam resonators, low velocity coupling is very easily achieved by merely moving the coupling location away from the center of the beam, as shown in Fig.…”

“…In particular, for a filter with center frequency and bandwidth , these stiffnesses must satisfy (6) where is a normalized coupling coefficient found in filter cookbooks [29]. Note from (6) that filter bandwidth is not dependent on the absolute values of resonator and coupling beam stiffness; rather, their ratio dictates bandwidth.…”

“…In this respect, these devices pose an important bottleneck against the ultimate miniaturization and portability of wireless transceivers. For this reason, many research efforts are focused upon strategies for either miniaturizing these components [1]- [5] or eliminating the need for them altogether [6]- [8].…”

A Novel Approach to Blind I/Q Mismatch & Carrier Offset Compensation

“…Since, in theory, the I/Q downconversion corresponds to a pure frequency translation, the fundamental image signal problem is basically avoided during the downconversion. In thismanner, the requirements for RF image rejection filtering are greatly relaxed in practice [1][2][3][4].…”

“…Instead, alternative receiver structures, like the direct conversion [1,2] and low-IF [1,3,4] architectures, are receiving more and more interest. The analog front-end of these types of receivers is partially based on complex or I/Q signal processing [5][6][7].…”