A fully integrated inductorless CMOS impulse radio ultra-wideband (IR-UWB) receiver is implemented using $0.18;{mu}m$ CMOS technology for 3-5 GHz application. The UWB receiver adopts the non-coherent architecture, which removes the complexity of RF architecture and reduces power consumption. The receiver consists of inductorless differential three stage LNA, envelope detector, variable gain amplifier (VGA), and comparator. The measured sensitivity is -70 dBm in the condition of 5 Mbps and BER of $10^{-3}$. The receiver chip size is only $1.8;mm;{ imes};0.9;mm$. The consumed current is 15 mA with 1.8 V supply.