Wireless Receiver Design Emphasizes Direct Conversion

With digital signals, the shortest path from the analog RF input to a digital signal ready for processing is highly desirable. Direct conversion translates the radio frequency of a signal to an equivalent bandwidth centered on DC (or zero Hz). At this low frequency range, the most inexpensive digital IC technology can be used for processing. Since power consumption of digital devices increases with clock frequency, baseband processing requires the least power for its operation. As is often the case, the advantages of any design approach may also present new design challenges. In a direct-conversion receiver, the advantage of eliminating IF stages means that the local oscillator is at the center frequency of operation. Exceptional balance and reverse isolation performance is required to avoid excessive radiation of the LO via the receiving antenna.