A 4th-order N-path filter in 40nm CMOS with tunable Gm-C stage and reduced center-frequency offset

As the demand for multi-mode and multi-band RF receiver blooms, traditional off-chip bulky and non-tunable filters such as SAW and BAW filter are no longer suitable for receiver chips. The newly appeared on-chip N-path filter becomes appealing due to its large-scale frequency tuning range, high Q and progress-scalable feature. However, conventional N-path filter is limited by its normally narrow passband and inevitable center-frequency offset. To overcome these two shortcomings, gm-C stages are proposed to compensate center frequency offset and obtain high out of band (OOB) rejection. This paper presented a 4th-order N-path filter with eliminated center-frequency offset and configurable bandwidth by 40nm CMOS technology.