Base Station Receiver Design Using a Direct-Conversion I/Q Demodulator
James Wong, Min Zou, Doug Stuetzle and Sunny Hsiao
Direct conversion (or low IF) receiv-er designs have been in existence for many years. They are widely used in cell phones and cordless tele-phones because of their simplicity and lower cost. Direct conversion receiver ICs have only recently met the level of performance required for base stations. However, the relentless drive to reduce the cost of next generation base stations compels attention to direct conversion architectures which offer a flexible approach to cover multi-ple RF standards and to simplify system design. Many benefits accrue from pushing channel selection into the baseband digital domain, particularly for multi-standard receivers. A problem with this approach, how-ever, is its susceptibility to interfering signals that are in-band to the receiver. This necessi-tates that the I/Q demodulator used in the direct conversion receiver is able to handle demanding dynamic range requirements that can be as high as 80 dB. This article reviews the issues specific to direct conversion receivers for base station applications, and describes a new RF direct conversion IC that takes great strides in resolving these issues.
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