A multirate reconfigurable cascade sigma delta modulator for multi-mode mobile terminals

A 2-2 cascade multirate sigma delta modulator targeting for GSM/ Bluetooth/ GPS/ WCDMA/ WLAN/ WiMAX application is designed in this paper. According to the needs of the customers and desired Quality of Service, the proposed modulator should be a power and area efficient reconfigurable sigma delta modulator with variable bandwidth and dynamic range. The multirate technique is introduced in the modulator to overcome the area and power penalities, which decreases the oversampling ratio of the 1^st stage integrators. The power consumption of a sigma delta modulator is primarily determined by the 1^st stage integrators in the chain which are sampled at a low rate in the multirate modulator. The performances of the modulator are preserved by increasing the rate of the rest of integrators whose contributions to power consumption are not so significant. The simulation results show that the proposed modulator fulfills the performance requirements of the mobile communication standards mentioned above. In comparison with the correspondingly conventional 2-2 cascade modulator structure, the proposed topology obtains similar performances and relaxes the speed requirements of the operational amplifiers in the 1^st stage.