This paper presents a Bluetooth low-energy (BLE) transceiver (TRX) achieving ultra-low-power operation for Internet-of-Things (IoT) applications. The proposed TRX utilizes a wide-bandwidth low-power fractional-N digital phase-locked loop (DPLL) as a central component to perform multiple roles: a direct frequency modulator for the transmitter (TX), an analog-to-digital converter (ADC) for the receiver (RX), a local oscillator for RX, and a frequency and phase synchronizer for the RX. The DPLL-based single-path downconversion method is adapted to halve the analog baseband circuit to further reduce the power consumption while maintaining a high interference rejection. A DPLL-based ADC with a digital-to-analog converter feedback greatly improves the ADC dynamic range, which improves the RX sensitivity and interference tolerance. By maximally reducing the required radio frequency and analog front-end components in RX, an RX power consumption of 2.3 mW is achieved with a -94 dBm sensitivity. The RX also satisfied all interference requirements with a certain margin. A 5.0-mW TX is achieved when delivering an output power of 0 dBm with a frequency-shift keying error of only 1.89%.