A Sub-GHz Multi-ISM-Band ZigBee Receiver Using Function-Reuse and Gain-Boosted N-Path Techniques for IoT Applications

To address the cost and universality of ultra-low-power (ULP) radios for Internet of Things (IoT) applications, a sub-GHz multi-ISM-band (433/860/915/960 MHz) ZigBee receiver is developed. It features a gain-boosted N-path switched-capacitor (SC) network embedded into a function-reuse RF front-end, offering concurrent RF (common-mode) and BB (differential-mode) amplification, LO-defined RF filtering, and input impedance matching with zero external components. Interestingly, not only the BB power and area are nullified, but also the loading effect between the RF and BB blocks is averted, resulting in better noise figure (NF). Unlike the existing N-path filtering, the described gain-boosted topology offers: 1) double RF filtering at both input and output of the RF front-end; 2) size reduction of the physical capacitors thanks to the Miller multiplication effect, and 3) LO-power saving by decoupling the mixer´s on-resistance to the ultimate stopband rejection. Together with a low-voltage LC-VCO with extensively-distributed negative-gain cells for current-reuse with the BB filters, the receiver achieves 8.1 ± 0.6 dB NF, 50 ± 2 dB gain and -20.5 ± 1.5 dBm out-of-band IIP3 at 1.15 ± 0.05 mW power at 0.5 V over the four ISM bands. The active area is 0.2 mm 2 in 65 nm CMOS.