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An energy-efficient crystal-less double-FSK transceiver for wireless body-area-network (WBAN) sensor nodes is implemented in 0.18-μm CMOS technology with a 1-V supply. The injection-locking digitally controlled oscillator (IL-DCO) replaces the crystal oscillator (XO), which leads to significantly reduce the energy consumption and system cost. With the proposed calibration method using an injection-locking detector (IL-detector), the frequency drift of DCO can be calibrated within 100-kHz accuracy over 100° temperature variation. For the full satisfaction to the WBAN requirements, such as wide range of quality of service in terms of data rate, bit error rate, and network coexistence, we adopt a scalable double-FSK modulation scheme with divider-based transmitter by a power-efficient switching modulator. As a result, the fabricated crystal-less double-FSK WBAN compatible sensor node transceiver consumes 1 and 2 mW in calibrating and transmitting modes, respectively, at a data rate of up to 10 Mb/s, providing an 80 MHz reference source with 100-kHz accuracy by auto-calibrated DCO.