A 2.5 GHz constant envelope phase shift modulator for low-power wireless applications

A low-power constant envelope phase shift modulator is presented. The circuit switches the phase of a constant amplitude carrier at the output according to the input digital data. The operation is based on a digital circuit and therefore has very low power consumption. A modulator test chip was fabricated in a 0.18 μm CMOS process. Experimental results verified the design principle of the modulator. The modulator consumes 2 mA and is suitable for low power wireless applications like sensor networks and personal area networks. Since the design is implemented as a digital circuit and has a broadband frequency response, the modulator can be used at various wireless bands. In addition, the modulator can be used to generate different modulation schemes by controlling the phase, and even amplitude, digitally through a phasor-combining circuit. Therefore, the modulator can potentially be used for software defined radio.