Systems and methods for magnetic field sensors with self-test

Patent metadata

Field	Value
Publication number	US-9851416-B2
Application number	US-201414337613-A
Country	US
Kind code	B2
Filing date	Jul 22, 2014
Priority date	Jul 22, 2014
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

Systems, methods and apparatuses for magnetic field sensors with self-test include a detection circuit to detect speed and direction of a target. One or more circuits to test accuracy of the detected speed and direction may be included. One or more circuits to test accuracy of an oscillator may also be included. One or more circuits to test the accuracy of an analog-to-digital converter may also be included. Additionally one or more IDDQ and/or built-in-self test (BEST) circuits may be included.

First claim

What is claimed is:

1. An apparatus comprising:
a detection circuit to detect speed and direction of a target, the detection circuit comprising:
one or more magnetic field sensing elements;
a first signal channel to output a first signal;
a second signal channel to output a second signal, wherein the first and second signals correspond to a position of the target in relation to the one or more magnetic field sensing elements;
an oscillator to provide an oscillating output; and
an analog-to-digital converter;

a first test circuit to determine if the apparatus is detecting speed and/or direction accurately, the first test circuit comprising a counter coupled to the signal channels such that the first signal channel increments the counter and the second signal channels decrements the counter, the first test circuit including circuitry to assert an error condition if a count of the counter exceeds a predetermined threshold;
a second test circuit coupled to the oscillator to determine whether the oscillator is oscillating within a predetermined frequency range, the second test circuit comprising a ramp generator to generate a voltage ramp signal that decays over time and resets upon detection of an edge of the oscillating output, and a comparator circuit to determine whether a voltage level of the voltage ramp signal is between a predetermined voltage range upon detection of the edge of the oscillating output;
a third test circuit coupled to the analog-to-digital converter to determine whether the analog-to-digital converter is operating with an expected accuracy, the third test circuit comprising an output to inject an analog test signal into an input of the analog-to-digital converter, an input coupled to receive a digital signal from the analog-to-digital converter representing a conversion of the analog test signal; and a comparator circuit to compare the digital signal to an expected value; and
a fourth test circuit coupled to receive the digital signal from the analog-to-digital converter, compute a rate of change of the output of the analog-to-digital converter, and determine whether the rate of change is within a predetermined range defined by a mechanical system to which the target is attached.

2. An apparatus comprising:
a detection circuit to detect speed and direction of a target, the detection circuit comprising:
one or more magnetic field sensing elements;
a first signal channel to process a first output signal generated by at least a first magnetic field sensing element of the one or more magnetic field sensing elements;
a second signal channel to process a second output signal generated by at least a second magnetic field sensing element of the one or more magnetic field sensing elements, wherein the first and second signals correspond to a position of the target in relation to the one or more magnetic field sensing elements;
an oscillator to provide an oscillating output; and
an analog-to-digital converter;

a first test circuit coupled to the first and second signal channels to compare the first and second signals to determine if the detection circuit is operating with an expected accuracy;
a second test circuit coupled to the oscillator to determine whether the oscillator is oscillating within a predetermined frequency range, the second test circuit comprising a ramp generator that generates a voltage ramp signal that decays over time and resets upon detection of an edge of an output signal of the oscillator;
a third test circuit coupled to the analog-to-digital converter to determine whether the analog-to-digital converter is operating with an expected accuracy; and
a voltage level test circuit to measure a voltage level of the voltage ramp signal after the voltage ramp signal has decayed for a period of time, the voltage level test circuit comprising a first comparator to compare the voltage ramp signal to a predetermined upper voltage and a second comparator to compare the voltage ramp signal to a predetermined lower voltage;
wherein the first test circuit comprises a counter circuit coupled to increment a count in response to the first output signal generated by the first magnetic field sensing element and decrement the count in response to the second output signal generated by the second magnetic field sensing element.

3. The apparatus of claim 2 wherein the magnetic field sensing elements comprise Hall Effect elements and/or GMR elements.

4. The apparatus of claim 2 wherein the first and second signals represent a difference between outputs of first and second ones of the one or more magnetic field sensing elements.

5. The apparatus of claim 2 wherein the period of time comprises a period of the oscillator.

6. The apparatus of claim 2 wherein the third test circuit comprises a switched capacitor resistor having at least one switch controlled by the oscillator output.

7. The apparatus of claim 2 further comprising a processor circuit to calculate a value of an output of the analog-to-digital converter circuit and compare the calculated average value to a predetermined value.

8. The apparatus of claim 7 wherein the processor circuit compares the calculated value to a predetermined maximum value.

9. The apparatus of claim 7 wherein the processor circuit generates the calculated value from a running average of the output of the analog-to-digital converter.

10. The apparatus of claim 7 wherein the processor circuit compares the calculated value to a maximum speed value, a maximum acceleration value, a direction value, or a combination thereof.

11. The apparatus of claim 2 further comprising an ADC test circuit to inject a predetermined analog voltage to an input of the analog-to-digital converter, receive a digital output signal from the analog-to-digital converter in response to the injected voltage, and to compare the digital output signal to an expected value.

12. The apparatus of claim 11 wherein the ADC test circuit injects the predetermined analog voltage to the input of the analog-to-digital converter at a predetermined time interval.

13. The apparatus of claim 12 further comprising a filter circuit to filter the digital output signal from an output of the analog-to-digital converter.

14. The apparatus of claim 11 wherein the ADC test circuit injects the predetermined analog voltage to the input of the analog-to-digital converter when the input of the analog-to-digital converter is within a predetermined range.

15. The apparatus of claim 2 further comprising an IDDQ and/or BIST test mode that can be activated during operation of the apparatus within a motor vehicle.

16. The apparatus of claim 15 wherein the IDDQ and/or BIST test mode is activated during a power-on sequence of the apparatus in response to ignition of the motor vehicle.

17. The apparatus of claim 2 further comprising:
at least one output terminal to carry signals representing the detected speed and direction of the target; and
a circuit to assert an error condition on at least one of the output terminals if an error is detected by the first, second, and/or third test circuit.

18. An apparatus comprising:
a detection circuit to detect speed and direction of a target, the detection circuit comprising:
one or more magnetic field sensing elements;
a first signal channel to output a first signal;
a second signal channel to output a second signal, wherein the first and second signals correspond to a position of the target in relation to the one or more magnetic field sensing elements;
an oscillator to provide an oscillating output; an

Assignees

• Allegro Microsysterns Llc
• Allegro Microsystems Llc

Inventors

• Scheller P Karl
• Burgess James E
• Snyder Steven E
• Moody Kristann L
• Fernandez Devon
• Foletto Andrea

Classifications

• G01P13/00

  Indicating or recording presence, absence, or direction, of movement (electric switches H01H; counting moving objects G06M7/00) · CPC title

• G01R23/005

  Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller (comparing phase or frequency of 2 mutually independent oscillations in demodulators) · CPC title

• G01P3/487

  delivered by rotating magnets · CPC title

• G01D5/24476 Primary

  Signal processing (G01D5/2448 - G01D5/24495 take precedence) · CPC title

• G01P21/02

  of speedometers · CPC title