A 900 MHz integrated discrete-time filtering RF front-end

The authors introduce a radio receiver architecture that avoids external intermediate frequency (IF) filters, while maintaining the selectivity required for narrowband frequency-multiplexed channels. The receiver is based on a subsampling architecture and operates in the 800-900 MHz range. It is a potential candidate for use in applications such as portable mobile data systems, personal communications devices, and cordless telephony. This receiver differs from a superheterodyne architecture in that the mixer is replaced by a sampling circuit and the intermediate frequency filters are replaced by a cascade of downsampling stages employing discrete-time filtering. The process of subsampling, sampling the input signal at a rate lower than the highest frequency components of the input signal, performs a function equivalent to mixing. Because the input is bandlimited by an analog RF filter, the Nyquist criterion is satisfied as long as the sampling rate is more than twice the bandwidth of this filter. The noise filter following the low noise amplifier (LNA) limits the noise bandwidth to prevent wideband noise from aliasing into the signal band and increasing the noise floor.