A 266-μW Bluetooth Low-Energy (BLE) Receiver Featuring an N-Path Passive Balun-LNA and a Pipeline Down-Mixing BB-Extraction Scheme Achieving 77-dB SFDR and −3-dBm OOB-B_{−1 dB}

This article reports an ultra-low-power (ULP) Bluetooth low-energy (BLE) receiver with an improved spurious-free dynamic range (SFDR). It features two passive-intensive RF techniques: an $N$ -path passive balun-LNA and a pipeline down-mixing baseband (BB)-extraction scheme. They together offer a high- $Q$ bandpass response at RF, and a high passive gain to suppress the noise of the BB hybrid complex filter. Specifically, the balun-LNA is a step-up triple-coil transformer aided by an $N$ -path switched-capacitor (SC) network to perform in-band voltage amplification, high- $Q$ bandpass filtering, $I/Q$ down-mixing, and input-impedance matching. Instead of using active amplifiers as the first-BB gain stage, we passively extract the four-phase ( $I/Q$ and differential) BB signals using a pipeline of passive-SC networks that can stack up the voltage gain. Prototyped in TSMC 28-nm CMOS, the BLE receiver consumes only 266 $\mu \text{W}$ , of which 75 $\mu \text{W}$ in the BB hybrid filter at 1 V, and 191 $\mu \text{W}$ in the LO divider + buffer at 0.6 V. Measured at the maximum RF-to-BB gain of 61 dB, the receiver exhibits a noise figure (NF) of 6.1 dB and an out-of-band (OOB)-IIP3 of 22.5 dBm. The corresponding SFDR is 77 dB for a 1-MHz BLE channel and a 10-dB minimum signal-to-noise ratio (SNR $_{\mathrm {min}}$ ). The OOB-B−1 dB is −3 dBm.