This paper proposes a low power wake-up baseband circuit used in Chinese Electronic Toll Collection (ETC) system. To reduce the static power consumption, a low power biasing strategy is proposed. The proposed circuit is fabricated in TSMC 0.18 μm technology with an area of 0.09 mm 2 . Its current consumption is only 2.1 μA under 1.8 V power supply. It achieves a sensitivity of 0.95 mV at room temperature with a variation of only ±28% over -35℃ to 105℃. This paper proposes a low power wake-up baseband circuit used in Chinese Electronic Toll Collection (ETC) system. To reduce the static power consumption, a low power biasing strategy is proposed. The proposed circuit is fabricated in TSMC 0.18 μm technology with an area of 0.09 mm 2. Its current consumption is only 2.1 μA at 1.8 V power supply. It achieves a sensitivity of 0.95 mV at room temperature with a variation of ± 28% over -35 ° C to 105 ° C.