The essential data link portions: clock generation, time-to-digital convertsion and PIE decoder with wide tolerance for the baseband processor in passive RFID (Radio Frequency Identification) devices are presented in this paper. For the consideration of low power and low-voltage supply, energy-aware structure with mixed counter and pre-counted addition are proposed for the circuit design. They also help to reduce the impact of frequency variation and simplify the oscillator. Fabricated in 130nm CMOS technology, the whole low-complexity circuit can operate at 0.3 V power supply.