A fully-integrated 8.4 Gb/s 2.5 pJ/b mobile memory I/O transceiver using simultaneous bidirectionaldual band signaling is presented. Incorporating both RF-band and baseband transceiver designs, this prototype demonstrates an energy-efficient and high-bandwidth solution for future mobile memory I/O interface. The proposed amplitude shift keying (ASK) modulator/demodulator with on-chip band-selective transformer obviates a power hungry pre-emphasis and equalization circuitry, revealing a low-power, compact and standard mobile memory-compatible solution. Designed and fabricated in 65-nm CMOS technology, each RF-band and baseband transceiver consumes 10.5 mW and 11 mW and occupies 0.08 mm ² and 0.06 mm ² die area, respectively. The dual-band transceiver achieves error-free operation (BER <; 10 ^-15 ) with 2 ²³ - 1 PRBS at 8.4 Gb/s over a distance of 10 cm.