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The proposed fully integrated digital-intensive system on chip (SoC) allows dual-mode protocols of Bluetooth low energy (BLE) 5.0 and IEEE802.15.4 with extended-range wireless connectivity and ad hoc mesh networks for Internet-of-Things (IoT) systems in wireless sensor networks. The SoC fully integrates a dc–dc converter, LDOs, a digitally controlled crystal oscillator (DCXO), a PHY, a microcontroller (MCU), a security engine, an SRAM, and an eFlash memory. A triple-supply configuration and low-voltage circuit design enable the SoC to be applied for a wide range of battery-powered systems energy-efficiently and to extend battery lifetime. The TRX employs a low insertion-loss on-die TRX switch with impedance matching circuits, a pseudodifferential current-mode class-D PA with HD2 calibration, a low-IF RX architecture with fast AGC algorithm and complex CT- $\Delta \Sigma $ ADCs, and a low-power all-digital phase-locked loop (ADPLL) with fast settling injection LDOs and an LMS-based two-point direct frequency modulation structure. The TRX implemented in a 28-nm CMOS process achieves an output power of +10 dBm with a calibrated HD2 of −63 dBc while consuming 45 mW and sensitivities of −98 dBm in 2-Mb/s BLE and −102 dBm in 256-kb/s IEEE802.15.4 at ${10}^{-3}$ BER while consuming 6 mW. [ABSTRACT FROM AUTHOR]