This paper presents a novel architecture for inductive proximity sensors using sigma delta modulation. The LC-oscillator is included in the sigma delta control loop providing amplitude regulation and high precision analog-to-digital conversion in one block. The circuit consists of a new LC-oscillator suitable for clocked tail current injection, two SC integrators and a clocked comparator forming the sigma delta modulator and a PLL providing the clock for synchron amplitude sampling. The circuit was realized in a 0.8µm CMOS technology of the Fraunhofer Institute for Microelectronic Circuits and Systems. Measurements show the capability of the system to distinguish even smallest differences in the target distance

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We present an integrable solution for detection of defective sensor elements using sigma-delta-(Σ∆)modulation and a matched filter. The sensor element is stimulated using a pseudo random binary sequence (PRBS). The sensor signal is read out and the analog output is digitized using a Σ∆-modulator. The binary pulse density stream of the Σ∆-modulator is the output of the sensor system and thus should ideally contains the PRBS. A matched filter has the task of detecting the pseudo random sequence in the pulse density stream and its sampled output is compared to a threshold thus making it possible to judge the functionality of the sensor element. By evaluating the magnitude of the matched filter output it is also possible to measure the sensor sensitivity. We present a discrete solution of this method, but an integrated chip using a standard 1.2µm CMOS-process has been designed and is being fabricated.

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