Multi-band OFDM ultra wideband (UWB) system is the leading proposal for the IEEE 802.15.3a standard. Multi-band pulsed-OFDM is an enhancement to this system that provides better performance with lower complexity and power consumption. In this paper we study the resolution of the analog to digital converter (ADC) that is required for both systems using the simulation results. The performance of both systems is evaluated with different ADC resolution in realistic situations using the measured indoor propagation channel models provided by the IEEE 802.15.3a standard and compared to that of a ideal infinite resolution i.e. ideal ADC. The simulation results show that in both systems four bits resolution are enough to a performance very near to the ideal case.