Breaking the Trade-off Between Input Impedance and Mixer Paths in Sub-Harmonic N-Path Mixer-First RF Front-end

The transparency property of the N-path mixers made the mixer-first RF front-ends to operate over wide frequency range with tunable impedance matching. However, the requirement of non-overlapping clocks for the RF-sampling N-path mixer causes the power consumption of the clock generation to overwhelm the receiver power consumption. Contrary to RF-sampling mixers, sub-harmonic mixers operating at low clock frequencies save the power consumption of clocking circuitry. However, sub-harmonic mixers are limited to operate at harmonic order of less than N/2 for N-path mixer-first RF front-ends due to their dependency on the number of mixer paths for impedance matching at the RF port. To address this issue, in this work, a novel impedance matching scheme by synthesizing a negative baseband impedance is proposed to facilitate the impedance matching at the desired higher-order harmonic of the sampling frequency. The proposed scheme breaks the tradeoff between the number of paths of the mixer, harmonic order and impedance matching of N-path mixer-first RF front-ends. Also, this work presents a design example using the proposed technique, operating at harmonic order greater than N/2 to validate the proposed idea.