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

Abstract

This article reports a 2.4-GHz Bluetooth low-energy (BLE) receiver with a number of passive-intensive RF functions to improve power efficiency and blocker resilience. It features a passive quadrature front end (QFE) built with a hybrid coupler plus two step-up transformers. They passively provide input-impedance matching, voltage gain, and single-ended-to-differential-I/Q RF generation. The four-phase RF outputs simplify the LO generator into a 2.4-GHz class-D voltage-controlled oscillator (VCO) that has an intrinsically boosted output swing, averting the power-hungry divider-by-2 and LO buffers. The frequency down-conversion based on a double-sided double-balanced (DSDB) cascaded mixer offers a high passive gain to reduce the noise and power consumption of the baseband (BB) circuitry while securing a high spurious-free dynamic range (SFDR) to tolerate the out-of-band (OOB) blockers. The BB circuitry is a power-efficient hybrid low-IF filter that employs a 2nd-order active-feedback notching to enhance the 1st-adjacent channel rejection. Fabricated in 28-nm CMOS, the BLE receiver exhibits a maximum RF-to-IF gain of 71 dB. The noise figure (NF) is 8.5 dB and the OOB-IIP3 is 20.1 dBm; they correspond to a 71.7-dB SFDR for a 2-MHz BLE channel and a 10-dB minimum signal-to-noise ratio (SNR $_{\min }$ ). The VCO exhibits a phase noise (PN) of −110/−119.1/−131 dBc/Hz at 1-/2.5-/10-MHz offset, corresponding to a figure of merit (FOM) of 188/189/189.1 dBc/Hz, respectively. The total power consumption of the receiver, including the VCO, is $167~{\mu }$ W.