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

C. Ji and R. Krenzke (Germany)


angular measurement, sensor interface, sigma-delta modulator, mixed analog-digital integrated circuits


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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