A custom UWB transceiver chipset is presented that communicates in three 550MHz-wide channels in the 3.1 to 5GHz band by using pulse position modulation (PPM). The transmitter uses an all-digital architecture and calibration technique to synthesize pulses with programmable width and center frequency. No analog bias currents or RF oscillators are required in the transmitter. The receiver performs channel-selection filtering, energy detection, and bit-slicing. The receiver circuits operate at 0.65V and 0.5V, and can turn on in 2ns for duty-cycled operation. The two chips are fabricated in a 90nm CMOS process, and achieve a combined 2.5nJ/bit at a data rate of 16.7Mb/s.