A Compact Reconfigurable N-Path Low-Pass Filter Based on Negative Trans-Resistance with <1dB Loss and >21dB Out-of-Band Rejection

N-path circuits have been used to implement high-quality tunable band-pass and notch filters with just switches and capacitors. Recently, non-reciprocal circuits such as circulators and isolators have also been reported as other applications of linear periodically time-varying circuits. However, low-pass filters (LPFs) based on N-path structures have not been reported. Traditionally, low-pass filters are implemented using passive LCs or active Gm-C/OTA-C structures. Poor quality and large size of inductors at lower frequencies limit the design of an integrated passive LPF. Active LPFs on the other hand usually offer poor noise and linearity performance with high power consumption. Here, for the first time we report a tunable N-path quasi-elliptic LPF. Since there is no inductor in the design, the filter is compact with loss of 0.9dB and 250MHz 3dB bandwidth. The OOB rejection is >20dB and the IB P1dB is +5dBm. The IB/OOB IIP3 are +15dBm/+16.5dBm and the NF is 2.1dB.