A new rom-less pulse shaper for 2.4 GHz ZigBee application

This paper presents a special automatic pulse shaper for 2.4 GHz ZigBee transmitters. To implement half sine shape needed for OQPSK pulse shaping used in ZigBee, a circuit was designed that consists of a clock generator, a customized current-steering digital to analog converter (DAC) and a low-pass filter (LPF). Every point of a sine shape is produced by adding or subtracting current sources. Clock generator produces required logical bits for the DAC. A customized fully differential quadrature current mode DAC produces 4 half sine outputs (I+, I-, Q+, Q-). This topology does not need any ROM or counter and is independent from digital section and results in reduced power consumption and die size. Furthermore, eliminating the binary DAC eliminates glitch effect too; so linearity of total system is improved. Simulation results show -36db THD at output signal by using 5-point for every quadrant. All of circuits are designed based on 0.18 μm TSMC CMOS technology with a single 1.8 volt power supply.