This paper presents the design of a fully integrated sub-microWatt CMOS ultra-wideband (UWB) pulse-based transmitter, aimed for low data rate wireless sensors networks. The transmitter consists of a current starving clock, an all-digital pulse generator, and a 2nd derivative Gaussian pulse shaping network with 50 Omega driving capability. The design is implemented in a standard CMOS 0.18 mum process. A typical pulse width of 170 ps is achieved. Two commonly used modulation schemes are investigated. Namely, on-off keying (OOK) and pulse-position modulation (PPM). The complete design occupies an area of 0.14 mm2 and consumes an average power of 326.3 nW at 200 Kpps (pulse-per-second) with a 1.5 V supply. At a maximum pulse repetition rate of 100 MHz, the transmitter consumes no more than 82 muW in power, which is among the lowest in transmitter designs reported to date