Don Tuite
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ED Online ID #13942 |
November 14, 2006
What’s new in analog switches and multiplexers? These chips are extending their reach from industrial and instrumentation equipment and communications infrastructure to consumer gear like AV receivers and cell phones, which need bandwidth and signal-amplitude flexibility. Component video needs larger switch arrays than composite video, but the configurations are much the same. Cell-phone audio requires simple single-pole single-throw (SPST) and single-pole double-throw (SPDT) switches for microphones, speakers and auxiliary outputs, and multimedia functions that add more switching complexity.
What are some key specs? On resistance (RDS(ON)) is critical for both video and audio, not only because of insertion loss, but also because it can vary with signal voltage, distorting the transfer characteristic and creating harmonic distortion and intermodulation products. In addition, the parasitic input and output capacitances associated with the MOS switch limit bandwidth. Also, there’s the allowable input signal range. Power consumption and the physical size of the package are significant factors as well.
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