This paper presents the architecture and circuit design of the reconfigurable frequency-modulated ultra-wideband (FM-UWB) transmitter for robust non-invasive short range communications. The transmitter employs a Δ-Σ fractional-N PLL with an amplitude-controlled quadrature relaxation VCO to generate a 2-FSK modulated triangular waveform. The differential triangular waveform outputs of the relaxation VCO directly modulate a dual-path LC VCO whose center frequency is set by a digitally configurable quasi-continuous frequency-locked loop (FLL) for nearly 600-MHz UWB signal generation. Experimental results of a 10 to 100 kb/s, 3.3 to 4.4 GHz FM-UWB transmitter in 0.18-μm CMOS are presented and future works are addressed.