In current wireless communication applications, high data rate, low power, and low cost are desirable because of the surging demand for enhanced performance, battery life, and cost-efficiency of the electronic devices. To satisfy the above requirements, UWB technologies in the 3.1-10.6 GHz band for communication systems with the average power emission restriction of -41.3 dBm/MHz has been adopted. Among different types of UWB systems, the impulse-radio UWB (IR-UWB) has been demonstrated to be low power, low cost, and highly immune to multipath fading, due to its less complicated carrier-free architecture and very low transmitting duty-cycle nature. In this project, CMOS integrated circuits have been developed for UWB communication systems.