Sensor apparatus and method for generating an output signal of a sensor apparatus

#The present invention relates to a sensor apparatus and a corresponding method for generating an output signal of a sensor apparatus.

#WO 99/42789 discloses an apparatus for detecting a passage between a point on a body and a reference position. The apparatus comprises a pair of magnetic field sensors, each of the sensors generating an output signal based on the size of the magnetic field which passes through the sensor. A difference-forming circuit is provided which receives the output signals of the sensors and generates a difference signal with a peak value when the point of the body is positioned between the pair of sensors. Furthermore, a peak value detector is provided which detects the peak value in the difference signal. Moreover, the apparatus comprises a threshold value circuit which receives the difference signal, for the purpose of generating a gate signal if the magnitude of the difference signal exceeds a threshold level, the gate signal enabling the peak value pulse to be forwarded to an output terminal of the apparatus, and preventing peak value pulses from being forwarded to the output terminal of the apparatus in the absence of the gate signal. Finally, the apparatus comprises a threshold value setting circuit for setting the threshold value in accordance with the magnitude of the difference signal.

#DE 197 01 262 A1 discloses a detector for passing magnetic articles with automatic gain control.

#FIG. 1 shows an illustration of a sensor apparatus for elucidating an embodiment of the method according to the invention; and

#FIG. 2 shows a flow diagram of the embodiment of the method according to the invention.

#In the sensor apparatus illustrated in FIG. 1, the rotational speed of a gearwheel 1 is detected by means of a Hall sensor, subsequently amplified by means of an amplifier 3 and then converted, with the aid of a comparator 4, into a pulse train whose frequency corresponds to the rotational speed of the gearwheel 1. The pulse train can then be tapped off at an output of the comparator 4 as first output signal 5. By way of example by means of [sic] magnetic DC fields acting on the Hall sensor 2 and/or offset voltages in the amplifier 3 can lead to a DC signal being superposed on an AC signal caused by the movement of the gearwheel in the Hall sensor 2, which leads to the switching points of the comparator 4 being shifted and, consequently, the pulse train of the output signal 5 attaining a different duty ratio. However, this corrupts the relationship between the pulse train of the output signal 5 and the movement of the gearwheel 1.

#In order to avoid this, in a known manner, a correction signal determined in a particular manner is subtractively combined with the output signal of the amplifier 3 in the comparator 4 acting as decision unit. This can also be achieved, moreover, for example by correspondingly altering the switching threshold of the comparator 4.

#The correction signal is generated by means of a digital control device 7, to which the output signal of the subtractor 6 is fed with the interposition of a digitally controlled analog amplifier 8 and an analog-to-digital converter 9. The analog-to-digital converter 9 operates according to the tracking principle. For this purpose, it has a subtractor 10, one input of which is connected to the output of the amplifier 8. The output of the subtractor 10 is connected to an input of a comparator 12, the other input of which is connected to the reference-ground potential 11. The output of the comparator 12 is connected to the control input of a counter 13, as a result of which the counting direction of the counter is controlled. The counter 13 is additionally connected up to a clock source 14. The counting result can be tapped off at an output of the counter 13 and is fed at [sic] binary word to a digital-to-analog converter 15, which generates a corresponding analog signal from it. This analog signal is passed to the subtractor 10, where it is subtracted from the output signal of the controllable amplifier 8. Overall, the subtractor 10, the comparator 12, the counter 13, the clock generator 14 and the digital-to-analog converter 15 form an analog-to-digital converter 9 which operates according to the tracking principle. This means that the binary word at the output of the counter 13 always follows the output signal of the amplifier 8 in which [sic] the comparator 12, depending on whether the analog signal produced from the binary word at the output of the counter 13 through the digital-to-analog converter is greater or less than the signal at the output of the amplifier 8, changes the counting direction of the counter 13 and thus tracks the binary word to the signal at the output of the amplifier.