This paper presents the system architecture, modeling, and design constraints for a baseband, integrated, CMOS, impulse ultra-wideband transceiver targeting very low power consumption on the order of 1 mW. Intended for a sensor network application, the radio supports low communication rates (∼100 kpbs) and ranging capabilities over short distances (∼10 m). Based on a "mostly digital" architecture, the analog complexity is reduced by moving the A/D convertor as close to the antenna as is reasonable. Pulses are generated from simple digital switches, overlaying the signal energy on the lower FCC UWB band (0-960 MHz). Reception is achieved using baseband gain blocks feeding a time-interleaved bank of low resolution A/D converters. A window of energy is captured in time and fed to the digital backend for processing. To save power and area, the digital backend implements only a pulse template correlation filter block overlaid with an additional spreading code. As a pulse template is used, no specific channel estimation or interference cancellation is assumed. The system performance is quantified for this case and implementation tradeoffs are explored with a strong focus on reducing power consumption. In particular, the issues of modulation choice, clock generation, gain and noise figure, ADC resolution, and digital signal processing requirements will be discussed.