45.2% Energy efficiency improvement of UWB IR Tx by use of differential PPM in 180nm CMOS

This paper discusses how Differential Pulse Position Modulation (DPPM) can increase the energy efficiency of an UWB impulse radio transmitter when compared to On-Off Keying (OOK). In DPPM, data words are coded in time intervals between consecutive pulses and it saves energy as less pulses are transmitted per bit. A method is shown for minimizing the energy con sumption per bit of a DPPM transmitter by choosing an optimal data word length. Measurement results show an energy efficiency improvement of 45.2%. The jitter of a low-power, low-performance reference clock used in the modulation could cause an unsatisfactory bit error ratio (BER). However, the measurements show that a 1.4 μW, 10 MHz ring oscillator (RO) can enable a BER better than 10-6. The measured transmitter has been implemented in a 180 nm CMOS technology.