A configurable architecture for implementing sigma-delta modulators

A configurable sigma-delta (SigmaDelta) modulator for sensor-conditioning applications is presented. The architecture allows the configuration of low-pass and band-pass modulators of different orders and topologies. The gains in all the stages are programmable permitting the adaptability of the circuit to different input signals and, therefore, facilitating the evaluation of MEMS and sensor prototypes. A prototype has been designed and simulated in a 0.35 mum CMOS technology. This switched-capacitor (SC) circuit can be configured as a first or a second order (low-pass or band-pass) modulator and is clocked at 2.56 MHz. Programmable gains are obtained by means of capacitor arrays, which have 5-bit resolution with a minimum capacitance value of 200fF. The digital programming of the whole circuit requires 104 bits for settling capacitor values and switch states. The architecture achieves high configurability with low additional distortion. Simulation results show a peak SNR of 58.8 dB, 66.58 dB and 48.3 dB for the three possible configurations with 64 OSR.