A 40μW 915MHz Receiver with Sub-Passive Third-Harmonic Mixer Achieving -88dBm Sensitivity and Multi-Channel Selection

This paper presents a 915MHz multi-channel receiver for ultra-low-power (ULP) applications. A sub-passive third-harmonic mixer is proposed to improve the front-end conversion performance at the ULP budget. Driven by the local oscillator (LO) that operates at one-third of the RF carrier frequency with a duty cycle of about 10%, the proposed mixer improves the front-end's noise figure (NF) to 15dB while reducing the LO power consumption by three times. The mixer also alleviates the requirement for LO phase accuracy. With the LO duty cycle ranging from 4% to 14%, the variation of the mixer performance is less than 10%, which allows a simple pulse generation approach without a precise duty cycle control circuit, thereby saving power consumption. A low-power frequency-locked loop (FLL) with a 196kHz tuning step facilitates channel selection. Additionally, a high-Q intermediate-frequency (IF) amplifier with an active inductor is used to suppress in-band interference and noise bandwidth. Implemented in a 65nm CMOS process and based on post-simulation results, the receiver achieves a sensitivity of -88dBm while consuming 40μW at a 250kb/s data rate. The receiver also performs an improved figure-of-merit (FoM) of 186dB with 26dB interference tolerance and a compact active area of 0.16mm²