A 6-31 GHz Tunable Reflection-Mode N-Path Filter

A 6-31 GHz reflection-mode N-path filter is implemented in 45 nm SOI technology. The filter is comprised of an on-chip hybrid coupler with through and coupled ports terminated with four-phase passive mixers. Each mixer provides a high impedance in-band and a 50-ohm impedance out-of-band, enabling reflection-mode bandpass filtering of the signal, with the center frequency set by the local-oscillator frequency. To increase selectivity, an active baseband load with adjustable bandwidth can be enabled to increase the roll-off to 12 dB/octave. The baseband loads between the two N-path mixers are shared to reduce size and power with the added benefit of creating a non-reciprocal filter response. Measurements show the filter can be tuned across 6–31 GHz with insertion loss <7 dB, typical return loss >10 dB, noise figure exceeding insertion loss by 1 dB at 6 GHz and 10 dB at 31 GHz, and in-band IIP3 of 1.4-6.3 dBm.