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With supplied by the battery, the low power consumption of OBU system chip in ETCS is demanded. This paper designs a low power wake-up circuits applied to OBU system chip. The circuit system extracts envelope signal from an amplitude shift keying (ASK) modulated 5.8 GHz carrier and converts it to digital signal. Only the envelop signal that the frequency of it is 14 KHz can produce the wake-up pulse, which effectively prevents error wake-up caused by other frequency signals. By incorporating an input impedance matching network, the wake-up circuits achieve input sensitivity of -35 dBm and the S11 of the match network is -19 dB with 50 Ω input impedance. Measurement results show the dc current is 6 μA from 2.4 V to 5 V supply. The wake-up circuits is fabricated in TSMC 0.18 μm RF CMOS 1P6M process and the entire chip occupies an areas of 375×330 μm2.