A component-invariant second-order switched-current sigma-delta modulator

The authors present the building blocks and design procedure necessary for creating a component-invariant second-order switched current (SI) sigma-delta modulator (ΣΔM). A novel SI second-order integrator block is paramount to the design. A voiceband (4-kHz) analog-to-digital (A/D) converter was designed and laid out in Northern Telecom´s 1.2-μm CMOS process. Final transistor level simulations on the netlist derived directly from the layout indicated a resolution of only 10 b, a result of excessive charge injection and clock feedthrough. The power and area requirements of the SI design are estimated to be 0.2 mW and 0.2 mm², respectively