A Reconfigurable Passive Mixer-Based Sub-GHz Receiver Front-End for Fast Spectrum Sensing Functionality

A reconfigurable parallel mixing subharmonic mixer (SHM)-based time-interleaved RF channelizer is proposed for fast spectrum sensing. The reconfigurable mixer operates as a double-balanced mixer (DBM), a double-balanced mixer with harmonic rejection (DBMHR), and an SHM. In contrast to conventional spectrum sensing receivers to detect RF frequency bands by sweeping local oscillator (LO) frequencies, the proposed receiver scans multiple frequency bands quickly through mode change of the reconfigurable mixer. The LO generation circuit employs a voltage subtractor-based phase adder and provides highly accurate 25% duty-cycle octet-phase LO signals. The front-end implements a high LO harmonic rejection ratio (HRR) in order to avoid signal corruption by LO harmonic mixing during spectrum sensing. In experiments, the proposed receiver achieves <40.3 dB conversion gain, <6.6 dB noise figure (NF), > -35.8 dBm in-band input-referred third-order intercept point (IIP3), > -22.3 dBm out-of-band IIP3, and an average 3rd LO HRR of 43 dB over 300-800 MHz in DBMHR mode. Over 600-1200 MHz in SHM mode, it shows >31.8 dB conversion gain, <10.4 dB NF, > -30.9 dBm in-band IIP3, and > -20.1 dBm out-of-band IIP3. The switching time between DBHHR and SHM modes is approximately 135 ns. The power dissipation is 24.7 mW from a 1.2 V supply voltage.