A High-Resolution Low-Power Incremental $\Sigma \Delta$ ADC With Extended Range for Biosensor Arrays

A calibration-free, high-resolution analog-to-digital converter designed for a bioluminescence sensor array employs incremental sigma-delta (ΣΔ) modulation to combine the advantages of oversampling with an input multiplexing capability. The resolution of incremental ΣΔ modulators can be improved significantly by means of a technique similar to extended counting. In the approach proposed in this paper, analog-to-digital conversion is accomplished with a two-step process in which the residual error from a second-order incremental ΣΔ modulator is encoded using a successive approximation ADC. By this means it is possible to achieve enhanced resolution and improved static linearity while maintaining a one-to-one mapping between individual input and output samples. An experimental implementation of the proposed modulator has been integrated in a 0.18-μm CMOS technology. Operating from a 1.8-V supply, it achieves a dynamic range of 90.1 dB and a peak signal-to-noise and distortion ratio (SNDR) of 86.3 dB at a conversion rate of 1 MSample/s, with 38.1-mW power consumption.