A 1-V 140-μW 88-dB audio sigma-delta modulator in 90-nm CMOS

A single-loop third-order switched-capacitor E-A modulator in 90-nm standard digital CMOS technology is presented. The design is intended to minimize the power consumption in a low-voltage environment. A load-compensated OTA with rail-to-rail output swing and gain enhancement is chosen in this design, which provides higher power efficiency than the two-stage OTA. To lower the power consumption further, class-AB operation is also adapted in the OTA design. Due to the relatively low threshold voltage of the advanced technology, no clock boot-strapping circuits are needed to drive the switches and the power consumption of the digital circuits is reduced. All the capacitors are implemented using multilayer metal-wall structure, which can provide high-density capacitance. The modulator achieves 88-dB dynamic range in 20-kHz signal bandwidth with an oversampling ratio of 100. The power consumption is 140 muW under 1-V supply voltage and the chip core size is 0.18 mm(2).