A fully-differential self-calibrated switched-current ΔΣ modulator

This paper describes a second order delta-sigma modulator that employs differential current mode transistor-only circuits and calibration techniques to achieve 12-13 bit resolution with better than 70 dB linearity. A differential first generation based S²I cell is adopted for its superior linearity and high transfer accuracy, while the use of an efficient self-calibrating technique minimizes integrator loss due to transistor mismatches and process variations. Simulation results indicate a -69 dB harmonic distortion for the current delay cell at a clock frequency of 1 MHz. The modulator occupies 2.73×2.13 mm² of silicon area in a 0.8 μm DPSM CMOS process