A fully integrated 802.15.4a-LRP-UWB-PHY- and ETSI-compliant impulse-radio ultra-wide-band (IR-UWB) transmitter (TX) front-end, powered by an RF-energy-harvester in 180 nm CMOS technology, is presented. The TX is working in the 7 GHz band transmitting with -42 dBm at 5.12 kbps data rate, consuming 1.89 μW. Two circuit implementations of RF-energy-harvesters are presented and, based on measurements, a combined and optimized structure is proposed which is capable of generating 5 μW dc-power at -13.3 dBm RF input power at a frequency of 868 MHz. According to the overall SoC power budget, this amount of harvested energy is sufficient to power the IR-UWB-TX front-end, an ADC with pre-amplifier and the digital core logic for a wireless bio-sensing chip. Furthermore, improvements of the presented IR-UWB TX circuitry are discussed.