A 1.8 V 15-bit 1 mW 2nd-Order Sigma-Delta Modulator

Low-voltage low-power sigma-delta modulators provide a critical interface in portable mixed-signal electronic systems. This paper deals with the design andimplementation of a low-voltage, low-power 2nd-ordersigma-delta modulator operating from a single 1.8 V powersupply using a conventional 3.3 V, double-poly, 0.35 μmCMOS process, based on fully-differentialswitched-capacitor techniques. All the circuit blocks areintegrated on one chip, and the input common-mode voltageis set at mid-rail, resulting in low power dissipation,minimum off-chip components, and high efficiency,flexibility and compatibility. The design is useful forvoice applications in personal communications systemssupplied by two nickel-cadmium or alkaline batteries. Themodulator exhibits a 15-bit dynamic range for a 7 kHzbandwidth, and a 14-bit dynamic range for a 20 kHzbandwidth at an oversampling frequency of 2.56 MHz. Thepeak SNDR reaches 62 dB. The complete 2nd-order modulatorhas a power dissipation of 0.99 mW, and occupies 0.31mm2 die area excluding bonding pads.