Design of Reconfigurable Digital IF Filter With Low Complexity

Abstract

Due to limited frequency resources, new services are being applied to the existing frequencies, and service providers are allocating some of the existing frequencies for newly enhanced mobile communications. Because of this frequency environment, repeater and base station systems for mobile communications are becoming more complicated, and frequency interference caused by multiple bands and services is getting worse. Therefore, a heterodyne receiver using intermediate frequency (IF) filters with high selectivity has been used to minimize the interference between frequencies. However, repeater and base station systems in mobile communications employing fixed IF filters cannot actively cope with the usage of multiple frequency bands, the application of various services, and frequency recycling. Therefore, this brief proposes a reconfigurable digital IF filter with variable center frequency and bandwidth while achieving high selectivity as existing IF filters. The center frequency of a filter can vary from 10 MHz to 62.5 MHz, and the filter bandwidth can be selective to one of 10 MHz, 15 MHz, and 20 MHz. The proposed digital filter also reduces the complexity of adders and multipliers by 38.81% and 41.57%, respectively, compared to an existing digital filter by using a filter bank and a multi stage structure. This digital IF filter is fabricated on a 130-nm CMOS process and occupies 5.90 mm2.