A Compact Reconfigurable N-Path Low-Pass Filter Based on Negative Trans-Resistance with <1dB Loss and >21dB Out-of-Band Rejection
In the past, 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. To date, however, low-pass filters (LPFs) based on N-path structures have not been reported. Traditionally, low-pass filters are implemented using passive LC implementations or active Gm – C/OTA-C structures. Poor quality factor and large size of inductors (and transmission lines) at lower frequencies limit the design of an integrated passive low-pass filter. Active low-pass filters on the other hand usually offer poor noise and linearity performance with high power consumption. In this work, for the first time we report a tunable N-path quasi-elliptic low-pass filter. Since there is no inductor in the design, the filter is compact with loss of 0.9dB and 250MHz 3dB bandwidth (BW). The out-of-band rejection is greater than 20dB and the in-band P1dB is +5dBm. The in-band and out-of-band IIP3 are +15dBm and +16.5dBm respectively, and the noise figure (NF) is as low as 2.1dB.