Variable reluctance sensor interfaces with signal pre-processing and methods of their operation
View Patent ↗The embodiments described herein can provide a variable reluctance sensor (VRS) interface that may reduce the probability of erroneous transitions in a resulting generated detect signal. As such, the VRS interface can improve the accuracy of position and/or motion determinations, and thus can improve the performance of a wide variety of devices that use variable reluctance sensors. To facilitate this, the VRS interface includes a pre-processing circuit configured to modify a VRS signal to prevent the modified VRS signal from dropping below a threshold value and generating erroneous transitions in the detect signal pulse between leading and lagging edges of a tooth. In one embodiment the pre-processing circuit comprises a peak and hold circuit. In another embodiment the pre-processing circuit comprises a resistor-capacitor circuit. In either case the pre-processing circuit can prevent erroneous transitions in the detect signal and thus may improve the performance and accuracy of the system.
1. A variable reluctance sensor interface for processing a variable reluctance sensor signal that reflects a magnetic flux variation that occurs when a tooth passes by a variable reluctance sensor, wherein the tooth has a leading tooth edge and a trailing tooth edge, the variable reluctance sensor interface comprising:
a pre-processing circuit configured to modify the variable reluctance sensor signal to prevent the variable reluctance sensor signal from dropping below a second threshold value between a first portion of the variable reluctance sensor signal corresponding to the leading tooth edge and a second portion of the variable reluctance sensor signal corresponding to the trailing tooth edge;
a leading edge comparator including a first input configured to receive the modified variable reluctance sensor signal and including an output configured to provide a leading edge signal responsive to the modified variable reluctance sensor signal reaching a first threshold value;
a trailing edge comparator including a first input configured to receive the modified variable reluctance sensor signal and including an output configured to provide a trailing edge signal responsive to the modified variable reluctance sensor signal reaching the second threshold value; and
a post-processing circuit configured to receive the leading edge signal and the trailing edge signal and generate a detect signal pulse having a width corresponding to a timing difference between the leading edge signal and the trailing edge signal.
2. The variable reluctance sensor interface of claim 1 wherein the tooth is on a trigger wheel coupled to a rotating shaft and wherein the detect signal pulse is used to determine an angular position of the rotating shaft.
3. The variable reluctance sensor interface of claim 1 wherein the pre-processing circuit comprises a peak and hold circuit.
4. The variable reluctance sensor interface of claim 3 wherein the peak and hold circuit comprise a diode coupled to a capacitor.
5. The variable reluctance sensor interface of claim 4 wherein the diode is a Zener diode having a breakdown voltage less than a minimum detectable VRS signal.
6. The variable reluctance sensor interface of claim 1 wherein the pre-processing circuit comprises a resistor-capacitor (RC) circuit.
7. The variable reluctance sensor interface of claim 6 wherein the RC circuit comprises a low pass filter.
8. The variable reluctance sensor interface of claim 6 wherein the RC circuit has a time constant selected to provide a frequency response sufficient for anticipated maximum rotation rate and width of the tooth.
9. A capacitor discharge ignition system for an internal combustion engine, comprising:
a variable reluctance sensor configured to sense passing of at least one tooth on a wheel in an internal combustion engine, the variable reluctance sensor configured to generate a variable reluctance sensor signal;
a pre-processing circuit configured to modify the variable reluctance sensor signal to prevent the variable reluctance sensor signal from dropping below a second threshold value between a first portion of the variable reluctance sensor signal corresponding to a leading tooth edge and a second portion of the variable reluctance sensor signal corresponding to a trailing tooth edge;
a leading edge comparator including a first input configured to receive the modified variable reluctance sensor signal and including an output configured to provide a leading edge signal responsive to the modified variable reluctance sensor signal reaching a first threshold value;
a trailing edge comparator including a first input configured to receive the modified variable reluctance sensor signal and including an output configured to provide a trailing edge signal responsive to the modified variable reluctance sensor signal reaching the second threshold value;
a post-processing circuit configured to receive the leading edge signal and the trailing edge signal and generate a detect signal pulse having a width corresponding to a timing difference between the leading edge signal and the trailing edge signal; and
an ignition control unit configured to control ignition timing based at least in part on the detect signal pulse.
10. The capacitor discharge ignition system of claim 9 wherein the wheel is coupled to a crankshaft in the internal combustion engine and wherein the detect signal pulse is used to determine an angular position of the crankshaft.
11. The capacitor discharge ignition system of claim 9 wherein the pre-processing circuit comprises a peak and hold circuit.
12. The capacitor discharge ignition system of claim 11 wherein the peak and hold circuit comprise a diode coupled to a capacitor.
13. The capacitor discharge ignition system of claim 12 wherein the diode is a Zener diode having a breakdown voltage less than a minimum detectable VRS signal.
14. The capacitor discharge ignition system of claim 9 wherein the pre-processing circuit comprises a resistor-capacitor (RC) circuit.
15. The capacitor discharge ignition system of claim 14 wherein the RC circuit comprises a low pass filter.
16. The capacitor discharge ignition system of claim 14 wherein the RC circuit has a time constant selected to provide a frequency response sufficient for anticipated maximum rotation rate and width of the tooth.
17. A method for processing a variable reluctance sensor signal that reflects a magnetic flux variation that occurs when a tooth passes by a variable reluctance sensor, wherein the tooth has a leading tooth edge and a trailing tooth edge, the method comprising:
modifying the variable reluctance sensor signal to prevent the variable reluctance sensor signal from dropping below a second threshold value between a first portion of the variable reluctance sensor signal corresponding to the leading tooth edge and a second portion of the variable reluctance sensor signal corresponding to the trailing tooth edge;
generating a leading edge signal responsive to the modified variable reluctance sensor signal reaching a first threshold value;
generating a trailing edge signal responsive to the modified variable reluctance sensor signal reaching the second threshold value; and
generating a detect signal pulse having a width corresponding to a timing difference between the leading edge signal and the trailing edge signal.
18. The method of claim 17 wherein the tooth is on a trigger wheel coupled to a rotating shaft and wherein the detect signal pulse is used to determine an angular position of a rotating shaft.
19. The method of claim 17 wherein the modifying the variable reluctance sensor signal to prevent the variable reluctance sensor signal from dropping below the second threshold value comprises using a peak and hold circuit.
20. The method of claim 17 wherein the modifying the variable reluctance sensor signal to prevent the variable reluctance sensor signal from dropping below the second threshold value comprises using a resistor-capacitor (RC) circuit that comprises a low pass filter selected to provide a frequency response sufficient for anticipated maximum rotation rate and width of the tooth.