2.4-GHz CMOS Bluetooth RF Receiver With Improved IM2 Distortion Tolerance

Abstract

A low-power CMOS sliding-IF RF receiver is presented for Bluetooth Low Energy (BLE) applications. It comprises an LNA, RF mixer, transconductance ( $g_{m}$ ) stage, IF mixer, transimpedance amplifier (TIA), and LO generation block. We present a comprehensive analysis of the second-order intermodulation (IM2) distortion that is induced by an in-band orthogonal frequency-division modulation (OFDM) blocker and its effects on the receiver input sensitivity. Based on the analysis, an in-band two-tone blocker tolerance test procedure is proposed, and an IM2 calibration circuit to enhance the receiver’s IM2 tolerance is presented. Furthermore, a conflict issue in the co-optimization of IM2 calibration at the IF mixer stage and dc offset calibration at the subsequent baseband amplifier stage is alleviated. This is achieved by employing a body bias control method for the dc offset calibration and a gate bias control method for the IM2 calibration. A BLE RF receiver integrated circuit was fabricated in a 65-nm RF CMOS process. Dissipating 3.55 mW from a 1-V supply, it achieves a gain control range from +2 to +62 dB, a minimum noise figure of 3 dB, and an out-of-band (OOB) single-tone blocker tolerance level of −10 dBm. Measurement results demonstrate that the proposed IM2 calibration circuit significantly improves the in-band two-tone blocker tolerance level by 7–12 dB, achieving its range from −41 to −31 dBm.