A High-Resolution Current-Mode Sigma-Delta Modulator

This paper describes techniques for the design of high-resolution oversampling analog-to-digital converters based on current memories. A key point is the reduction of non-linearities, in particular those introduced by the current switches. A current-memory cell with very high precision and linearity has been designed and used in an experimental 3rd order ¿-¿ modulator in a 0.8 micron digital CMOS process. A linearity of better than 14-bit and a maximum SNDR of 80 dB has been measured for an oversampling ratio of 64.