A low-power dual-mode sigma-delta modulator using charge-steering opamps

摘要

The charge-steering concept is applied to opamps as a means of conserving power. The opamp is the heart of the sigma-delta modulator circuit and the part in which the major portion of the power consumption is dissipated. This work presents a dual mode sigma-delta modulator for two wireless standards, GSM and Bluetooth. It achieves dual-mode operation with the same sampling frequency, while the capacitor values and the embedded quantizer are changed. The modulator achieves 65/50 dB SNR over a bandwidth of 0.2/1 MHz with an over sampling ratio of 120/24 and consumes 3.7/3.6 mW of power in GSM/Bluetooth modes, respectively. The charge-steering opamp consumes about 40% of the total power consumption.