A 90 nm-CMOS IR-UWB BPSK Transmitter With Spectrum Tunability to Improve Peaceful UWB-Narrowband Coexistence

A new ultra wideband (UWB) pulse generator covering a -10 dB bandwidth of 2.4-4.6 GHz with a tunable center frequency of 5-5.6 GHz to mitigate coexistence issues of impulse radio UWB (IR-UWB) systems and IEEE802.11.a WLAN or other narrowband (NB) systems in 90 nm-CMOS technology is proposed. The UWB pulse is generated based on frequency up-conversion of the first derivative of the Gaussian pulse, which creates an adjustable null in the frequency spectrum. Simulation results show that employing the proposed pulse generator mitigates the mutual interference between UWB and WLAN systems, significantly. The proposed transmitter consists of a low frequency signal generator, an LC oscillator and a mixer, whose output directly drives the antenna using a matching on-chip transformer. Two control signals change the bandwidth and center frequency of the transmitted spectrum depending on the NB frequency and considering process, supply voltage and temperature (PVT) variations. A fast start-up circuit is used in the LC oscillator using current pulse injection and together with the mixer is duty cycled to reduce the power consumption. Post-layout simulation results show a null depth of 23 dB for a null bandwidth of 100 MHz. The energy/pulse and energy/pulse normalized to the output voltage amplitude are 14.4 pJ/pulse and 35.7 pJ/(pulse-V) from a 1-V supply for a pulse rate of 860 Mpulse/s with an active circuit area of only 0.18 mm².