Sigma-Integration Analog to Digital Converter, Idea, Implementation and Results

The paper presents a new analog signal to digital representation conversion technique. The proposed approach tries to combine and preserve significant excellent features of double integration and sigma-delta analog to digital converters. The proposed AD-converter is constructed for a direct conversion of two analog signals ratio to the digital domain. The design uses an oversampling technique and the digital output resolution and bandwidth can be tuned by digital data post-processing. Other outstanding feature is an accurate area under signal curve measurement. The output data rate is constant (unlike for voltagefrequency converters) and the response time is maintained short without need of high modulator switching frequency. The described AD-converter features are a big advantage for the spectrophotometric absorbance measurement. Most of other measurement applications of AD-converters request mainly a great relative accuracy of conversion, but the absorbance is computed as a logarithm of the measured ratio between the measurement and the reference optical sensor response. The developed converter is already successfully used in serially produced UV-VIS spectrophotometric HPLC detectors. The converter has some drawback as well, the borders of sampling interval burden by some jitter although it has no influence on accumulated area computation.