A Widely Tunable N-Path Frequency-Selective Limiter for Self-Adaptive Interference Suppression

This paper reports the first widely tunable N-path frequency-selective limiter (FSL). Eight stagger-tuned 4-path filters are alternately summed to establish a 4-channel BPF with a steep roll-off between the passband and the stopband. The limiting action of an FSL is realized by autonomously modulating the frequency separation between each of the two 4-path filters within a channel to control the channel's passband gain. For input signals below −2 dBm, the FSL behaves as a conventional BPF with a 250 MHz bandwidth. At each input spectral component exceeding this limiting threshold, the FSL provides a variable notch in its passband with increasing attenuation of −10 dB for each +10-dB increase in the input component power to maintain the troubling tone output power below −1.3 dBm. The implemented 4-channel FSL using $0.18-\mu \mathrm{m}$ CMOS is tunable from 0.3 GHz to 1 GHz and achieves a NF of 14.5 dB.