Abstract: Most of the traditional band-stop filters are realized by all-passive components, and there are problems such as the difficulty of adjusting the bandwidth of the stop-band and the large area of the inductor. Using TSMC 180 nm CMOS technology, this paper proposes an adjustable-bandwidth band-stop filter based on an N-path notch filter. The circuit consists of two second-order N-path notch filters and a transconductance cell. The frequency of the two channels is shifted upward and downward with respect to the total output frequency to achieve a tunable stop-band bandwidth of the filter. At 1.8 V supply voltage, using Cadence Spectre RF simulation, the results show that the filter gain is greater than -2 dB,the notch frequency is adjustable from 0.3 GHz to 1.2 GHz, the stop-band bandwidth is adjustable from 20 MHz to 48 MHz, and stop-band rejection is 12 dB. When the frequency deviation is 150 MHz, IIP3 is 9.8 dBm, F_N is 3.5 to 6.5 dB. The proposed band-stop filter not only achieves a bandwidth-tunable function, is easy to integrate with a simple circuit structure, but also improves the overall circuit performance which provides a useful solution for multi-standard, multi-frequency radio applications.

Key words: band-stop filters, tunable bandwidth, transconductance cell, CMOS technology, tunable notch frequency