This paper describes an ultra-wideband (UWB) transmitter architecture for secure proximity communication. The transmitter achieves high security by utilizing a pseudorandom scrambling method for both frequency hopping in frequency domain and pulse position modulation (PPM) in time domain. In addition, the low transmitted power of -70dBm/MHz not only makes it difficult for other receivers to detect the signal but also makes the transmission worldwide compliant with existing wireless standards. A prototype 3-4GHz proximity transmitter is implemented in 0.18μm CMOS. The transmitter achieves 1Mb/s data rate with 0.3mW power from a 1.8V supply.