Integrated Sensor Interface with Dual Delta-Sigma ADC and CORDIC Algorithm for Angular Measurement of 0.04 Accuracy

C. Ji and R. Krenzke (Germany)

Keywords

angular measurement, sensor interface, sigmadelta modulator, mixed analogdigital integrated circuits

Abstract

Integrated contact-less angular measurement systems for high resolution requirement use magnetoresistive sensors and an analog and digital mixed-signal read out and signal processing circuit as sensor interface. The presented interface circuit consists of two fully differential 2 nd -order sigma-delta (Σ∆) modulator ADC channels for sine and cosine wave inputs, each followed by a digital decimation filter, offset and gain correction stages. Sine and cosine channels are cartesian-to-polar converted by the CORDIC algorithm. The Σ∆−modulator is clocked at 500kHz sampling frequency and achieves 81dB SNDR within a 3.9-kHz signal bandwidth and a 125-mV dynamic input range. The measured 3-σ angular error of the complete interface is 0.046° within a mechanically represented angular range of 180°. The circuit has been integrated in a 0.35-µm CMOS technology and the analog part including pads occupies 0.9mm2 . The digital part has 7000 gates, which corresponds to 0.4mm2 , and is synthesized together with other chip control logic. The current consumption of the interface circuit without sensor is 5.4mA.

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