Method and circuit configuration for processing the output signals of a rotational speed sensor

Claim 1

A circuit configuration for processing the output signal of a rotational speed sensor which provides an alternating voltage signal comprising a low-pass filter input circuit for attenuating high-frequency interfering signals and comprising amplifying and pulse-generating circuits, wherein a smoothing filter (TP1, TP2, 5, 6) is inserted into the input circuit between the rotational speed sensor (2) and the amplifying and pulse-generating circuits, which smoothing filter contains a first low-pass filter (TP1) for attenuating the high-frequency interfering signals and forming a useful signal (I1), a second low-pass filter (TP2) for obtaining a reference signal, and wherein the signals obtained by means said low-pass filters, namely the useful signal and the reference signal, are fed to a comparator (7) whose output signal represents the processed sensor signal; wherein the second low-pass filter (TP2) for the formation of said reference signal (I2) has a limit frequency which is below the lowest useful frequency of the sensor signal; wherein the first low-pass filter (TP1) for the attenuation of the high-frequency interfering signals has a limit frequency which is in the useful frequency range and is chosen such that the amplitudes of the useful signals (I1) are approximately the same above the limit frequency; wherein the useful signal (I1) and the reference signal (I2) are fed to the two inputs of the comparator (7); wherein impedance transformers (5, 6) are respectively inserted between the low-pass filters and the comparator (7); and, wherein a first resistor (RHY) is interposed in the signal lines between the impedance transformer (6) and the comparator (7), on which resistor a difference voltage can be generated by means of a first difference amplifier (8) controlled by the output signal of the comparator (7) and by means of a first current mirror circuitry (9), which difference voltage is opposed to the actuating signal of the comparator (7), that is the difference (I1, I2) between the useful signal and the reference signal, and thereby cause a switching hysteresis.