—An energy detector designed in a 0.18μm CMOS technology and intended for a non-coherent impulse-radio UWB receiver is presented in this paper. The proposed circuit exploits the quadratic current characteristic of saturated MOS transistors to square input pulses that cover the whole UWB bandwidth. The integral is computed with a Gm-C architecture connected to the squarer using a flipped voltage follower current sensor. A behavioural model of the receiver is developed in order to put the proposed circuit in the perspective of the complete system and to translate the transistor-level figures of merit in communication system parameters. The energy detector