Detection of Defective Sensor Elements Using Σ∆-Modulation and a Matched Filter

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.