This study reports a frequency-modulated ultra-wideband transmitter optimised for low-power consumption. The chip includes a sub-oscillator tunable from 0.1 to 4 MHz, a radio-frequency oscillator tunable from 3.0 to 4.5 GHz, and an output power amplifier with a matching network. Depending on the channel selected, the measured transmitter consumes between 440 and 640 μW of power to produce −14 dBm continuously to a 50 Ω load. Two power supplies are used to reduce the effect of wasted voltage headroom between circuit blocks. Fabrication is done using the International Business Machines Corporation 130 nm complementary metal–oxide–semiconductor technology on a 1 mm × 1 mm loose die, the circuit occupies 0.2 mm².