IMEC Digital UWB Transmitter

IMEC’s 90nm CMOS digital UWB transmitter is the first ever published IEEE 802.15.4a standard-compliant transmitter. It covers all the frequency bands of the standard up to 10GHz and is especially suited for application in low-power wireless sensor networks. The transmitter outperforms state-of-the-art low-power narrowband transmitter implementations.

The IEEE 802.15.4a standardization committee recently proposed an alternative physical layer for ZIGBEE providing positioning on top of low cost, low power and scalable data range using UWB as key technology. IMEC designed the transmitter IC based on the signal structure depicted in the standard. The chip consists of a digitally-controlled oscillator, a programmable frequency divider, a unique digital RF modulator and an early-late detector for frequency calibration of the oscillator.

The digitally controlled oscillator produces the RF carrier for all bands between 3 and 10GHz. The correct RF frequency is generated by a phase-aligned frequency locked loop instead of a traditional phase locked loop (PLL). This novel approach substantially reduces the start-up time to only 2ns and consequently reduces the signal duty cycle to only 3% resulting in very low power consumption. In addition, the technique also truncates the accumulative jitter process.

The transmitter has been designed in a 90nm digital CMOS technology with 1V power supply. Measurements on silicon show a power consumption for the transmitter of 0.65nJ per 16 chips burst (40pJ/pulse) at 3.5GHz carrier frequency and 1.4nJ per 16 chips burst (87pJ/pulse) at 10GHz. For the mandatory mode, this corresponds to 0.65mW to 1.4mW for 1Mbit/s data rate which outperforms state-of-the-art low-power narrowband transmitter implementations. The ultra-low power is obtained by switching off the entire transmitter between each burst and optimally exploiting the low power advantages of low duty-cycle communication.

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