This article proposes a compact low-power sub-2.4-GHz transceiver (TRX) with a all-digital phase-locked loop (ADPLL)-based transmitter (TX) and a single-path phase-tracking receiver (RX) in a 40-nm CMOS process. To meet the requirements for low output power in the medical band as well as to reduce power consumption, a single-ended class-E power amplifier (PA) with a duty-cycle-controlled strategy is proposed. A fully integrated on-chip matching network is designed to satisfy the impedance matching criteria for the class-E PA. The issues of the 2nd-order and the 3rd-order harmonic suppression are resolved by a series resonator and a capacitor in parallel with a segmented transformer, respectively. In the RX, the on-chip transformer also serves as an input impedance matching network for the low-noise transconductance amplifier (LNTA), reducing the required transconductance through passive reverse voltage gain. The transformer is capable of suppressing noise. The structure of the matching network only requires one transformer and one inductor, thereby reducing the count of passive components. Additionally, it features an embedded transmitter/receiver (T/R) switch function without insertion loss. The proposed 8-port transformer makes the layout more flexible and compact. The TX consumes 2.27 mW at ?10-dBm output power and 5.45 mW at 0 dBm. A 2nd-order harmonic distortion of ?52.36 dBm and a 3rd-order harmonic distortion of ?50.67 dBm are measured, respectively. The RX consumes 2.25 mW and achieves a sensitivity of ?93 dBm. The proposed TRX with reused matching networks results in an active silicon area of only 0.48 mm2.