Summary: In this paper we propose a novel functional amplifier suitable for low-power wireless receivers in a wireless sensor network. This amplifier can change input threshold level as carrier sensing level, since it has a minimum input amplitude to be amplified. A simple rail-to-rail output is suitable for a subsequent digital interface. The target frequency is 433 MHz, and the maximum voltage gain is 11 dB. The standby power is 39.5 nW, and the active power is 352 µW. The chip area is 8224 µm2.