23.4 A 167 μW 71.7dB-SFDR 2.4GHz BLE Receiver Using a Passive Quadrature-Front-End, a Double-Sided Double-Balanced Cascaded Mixer and a Dual-Transformer-Coupled Class-D VCO

The Bluetooth Low-Energy (BLE) receivers evolved from their traditional active RF front-ends [1, 2] to recent passive RF front-ends [3, 4] that aim to improve the power efficiency and blocker resilience. Without the bias current and nonlinearity of the gm - based LNA, a passive-intensive design with mainly inductor (transformer), capacitor and switch, allows substantial power saving and better linearity, while preserving a noise figure (NF) adequate for short-range IoT connectivity. Yet, the I/Q LO generation still bottlenecks the power reduction, as it primarily involves a double-frequency VCO, a divider-by-2 and LO buffers. This paper reports a $167 \mu W 2.4$ GHz BLE receiver featuring a number of passive-intensive RF functions. Specifically, the co-design between a passive quadrature front-end (QFE) and a 2.4GHz dual-transformer-coupled Class-D VCO averts the power-hungry divider-by-2 and LO buffers. Together with a double-side double-balanced (DSDB) cascaded mixer and a hybrid low-IF filter, our receiver achieves 71dB gain, an 8.5dB NF and a 20.1dBm out-of-band (OOB) IIP3. It corresponds to a 71.7dB spurious-free dynamic range (SFDR) that determines the capability of the receiver to tolerate the blockers [3].