This paper describes a low-cost realization of a precision capacitance measurement instrument. The method is based on synchronous modulation and demodulation operating at a frequency of 100 kHz. A two-channel multiplying digital-to-analogue converter is used to generate a sinusoidal drive voltage and to perform multiplication with the demodulation signal. The modulation and demodulation signals are generated using a direct digital synthesizer, which is implemented using a field programmable gate array. Experimental results show a reproducibility of better than ±0.005% in the range from 50 pF to 600 pF.
An integrated GMR (Giant-Magnetic-Resistance) sensor is presented for 3600 angular measurements of rotating magnetic fields in automotive applications. The spin-valve GMR-layers are directly applied to a standard semiconductor 0.22,um CMOS process by vertical integration of the sensorbridges atop of active circuitry. The entire integrated anglesensor comprises 2 orthogonal magnetized GMR-bridges for sine and cosine signal measurements, and the subsequent signal conditioning circuitry. The entire angular sensor is designed to work in harsh automotive environment in a temperature range of -40°C to 150°C. The strength for best precision covers a wide range from 20 to 50 mT. The resulting angular information itself can be obtained by SPI-readout and calculating the arc-trigonometric function of the bridge signals with a resolution of > 13bit in an auxiliary microcontroller. After individual calibration to compensate for production spread an accuracy of typical 0.50 is achieved.I.
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