Magnetic pole insensitive switch circuit

• US 6,356,741 B1
• Filed: 06/22/1999
• Issued: 03/12/2002
• Est. Priority Date: 09/18/1998
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Forrest, Glenn A., Vig, Ravi, Bilotti, Alberto
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US09/338,668
• Time in Patent Office: 994 Days
• Field of Search: 455/90, 455/550, 455/351, 379/420, 379/433, 307/116, 327/511
• US Class Current: 455/90.1
• CPC Class Codes: H03K 17/9517 using galvanomagnetic devices
• CPC Class Codes: H03K 17/97 using a magnetic movable element

Abstract

A switch which is magnetic pole insensitive is described. The switch includes a Hall effect sensor coupled to a threshold circuit which provides an output signal indicative of the proximity of a magnet, and hence a magnetic field, to the Hall effect sensor regardless of the orientation of the magnet to the Hall effect sensor.

Claims

1. A circuit comprising:

a sensor having at least one output port at which a first signal voltage is provided in response to the presence of a magnetic field of a first polarity and at which a second signal voltage is provided in response to the presence of magnetic field of a second polarity; and

a detector having at least one input port coupled to the at least one output port of the sensor and an output port at which an output signal is provided, the output signal being indicative of the presence of said magnetic field of said first polarity and the presence of said magnetic field of said second polarity, said detector comprising a first circuit for comparing said first signal voltage to a first threshold level and a second circuit for comparing said second signal voltage to a second threshold level, wherein said first and second threshold levels are adjustable with a common adjustment mechanism.

2. The circuit of claim 1 wherein said sensor is a Hall element.

3. The circuit of claim 1 wherein said magnetic field is provided by an article and said detector output signal is indicative of the article being positioned within a predetermined distance of said sensor.

4. The circuit of claim 1 wherein said detector is a comparator.

5. The circuit of claim 1 wherein said first circuit comprises a first differential pair circuit coupled to a first output port of said sensor and said second circuit comprises a second differential pair circuit coupled to a second output port of said sensor and wherein said detector further comprises a first resistor coupled to an input of said first differential pair circuit for setting said first threshold level, a second resistor coupled to an input of said second differential pair circuit for setting said second threshold level, and a current source coupled to said first and second resistors for varying the first and second threshold levels by varying the current through said first and second resistors.

6. The circuit of claim 1 wherein said detector further comprises an output driver having an input port coupled to an output of said first circuit and to an output of said second circuit and wherein said output driver further has an output port at which said output signal of said detector is provided.

7. In a wireless communication device, a switching system for providing a signal in response to an article which provides a magnetic field, the switching system comprising:

(a) a sensor for sensing the magnetic field of the magnetic article, said sensor for generating a first signal voltage having a signal voltage level which is proportional to a magnetic field having a first polarity and a second signal voltage having a signal voltage level that is proportional to a magnetic field having a second different polarity; and

(b) a threshold detection circuit coupled to the sensor to receive the first and second signal voltages and responsive to a supply voltage to provide an output signal having a first value when said magnetic article is within a predetermined distance of the sensor regardless of the polarity of the magnetic field, said threshold detection circuit comprising a first circuit for comparing said first signal voltage to a first threshold level and a second circuit for comparing said second signal voltage to a second threshold level, wherein said first and second threshold levels are substantially constant in response to variations in said supply voltage.

8. The switching system of claim 7 wherein:

said sensor is a magnetic-field-to-voltage transducer for generating a first signal voltage having a signal voltage level which is proportional to a magnetic field having a first polarity and a second signal voltage having a signal voltage level that is proportional to a magnetic field having a second different polarity; and

said threshold detection circuit is coupled to said magnetic-field-to-voltage transducer to receive the first and second signal voltages and to provide an output signal having a first value when the article is within the predetermined distance of said magnetic-field-to-voltage transducer regardless of the polarity of the magnetic field with respect to said magnetic-field-to-voltage transducer.

9. The switching system of claim 8 wherein;

said magnetic-field-to-voltage transducer is a Hall element circuit; and

said threshold detection circuit is a comparator coupled to said Hall element circuit.

10. The switching system of claim 9 wherein said comparator is a window comparator comprising first and second differential pair circuits, each of said first and second differential pair circuits having an input terminal coupled to one of a pair of outputs from said Hall element circuit and an output terminal coupled to an output terminal of said comparator.

11. The switching system of claim 10 further comprising first and second output amplifier stages, each of the output amplifier stages coupled between a respective one of the output terminals of the first and second differential pair circuits and the output terminal of said comparator.

12. The switching system of claim 7, further comprising a temperature and voltage bias circuit coupled to said comparator, said temperature and voltage bias circuit for maintaining operating signals in said threshold detection circuit within a predetermined range of operating signal levels in response to changes in said supply voltage and operating temperature.

13. A switching system for providing a signal in response to an article which provides a magnetic field, the switching system comprising:

(a) a sensor for sensing the magnetic field of the magnetic article, said sensor for generating a first signal voltage having a signal voltage level which is proportional to a magnetic field having a first polarity and a second signal voltage having a signal voltage level that is proportional to a magnetic field having a second different polarity, wherein said sensor is a Hall element circuit;

(b) a threshold detection circuit coupled to the Hall element circuit to receive the first and second signal voltages and responsive to a supply voltage to provide an output signal having a first value when said magnetic article is within a predetermined distance of the sensor regardless of the polarity of the magnetic field with respect to said Hall element circuit, said threshold detection circuit comprising a first circuit for comparing said first signal voltage to a first threshold level and a second circuit for comparing said second signal voltage to a second threshold level, wherein said first and second threshold levels are substantially constant in response to variations in said supply voltage, wherein said threshold detection circuit is a window comparator comprising first and second differential pair circuits, each having an input terminal coupled to one of a pair of outputs from said Hall element circuit and an output terminal coupled to an output terminal of said comparator; and

(c) a filter and level shifter circuit coupled between said Hall element circuit and said comparator.

14. A switching system for providing a signal in response to an article which provides a magnetic field, the switching system comprising:

(a) a sensor for sensing the magnetic field of the magnetic article, said sensor for generating a first signal voltage having a signal voltage level which is proportional to a magnetic field having a first polarity and a second signal voltage having a signal voltage level that is proportional to a magnetic field having a second different polarity, wherein said sensor is a Hall element circuit;

(b) a threshold detection circuit coupled to the Hall element circuit to receive the first and second signal voltages and responsive to a supply voltage to provide an output signal having a first value when said magnetic article is within a predetermined distance of the sensor regardless of the polarity of the magnetic field with respect to said Hall element circuit, said threshold detection circuit comprising a first circuit for comparing said first signal voltage to a first threshold level and a second circuit for comparing said second signal voltage to a second threshold level, wherein said first and second threshold levels are substantially constant in response to variations in said supply voltage, wherein said threshold detection circuit is a window comparator comprising it and second differential pair circuits, each having an input terminal coupled to one of a pair of outputs from said Hall element circuit and an output terminal coupled to an output terminal of said comparator;

(c) first and second output amplifier stages, each of the output amplifier stages coupled between a respective one of the output terminals of the first and second differential pair circuits and the output terminal of said comparator; and

(d) an output/buffer amplifier stage having an in put terminal coupled to the output terminal of each of said first and second output amplifier stages and having an output terminal coupled to the output terminal of said comparator.

15. A cellular telephone comprising:

a base;

a cover having a first end movably coupled to said base and a second end;

a magnetic article disposed in the second end of said cover, said magnetic article having a first pole and a second pole; and

a switch disposed in said base, said switch comprising;

a sensor for sensing the magnetic field of the magnetic article, said sensor for generating a first signal voltage having a signal voltage level which is proportional to a magnetic field having a first polarity and a second opposite signal voltage having an opposite signal voltage level that is proportional to a magnetic field having a second different polarity; and

a comparator coupled to the sensor to receive the first and second signal voltages and to provide an output signal having a first value when said magnetic article is within a predetermined distance of the sensor regardless of the polarity of the magnetic field.

16. The cellular telephone of claim 15 further comprising a control circuit coupled to said switch.

17. The cellular telephone of claim 15 wherein said sensor is provided as a magnetic-field-to-voltage transducer which generates at output terminals a first signal voltage having a first signal level voltage which is proportional to a magnetic field having a first polarity and a second signal voltage having a second signal voltage level that is proportional to a magnetic field having a second different polarity.

18. The cellular telephone of claim 17 wherein:

said magnetic-field-to-voltage transducer is a Hall element; and

said comparator is a window comparator.

19. The cellular telephone of claim 18 wherein said comparator receives signals from said Hall element and provides an output signal having a first value when said magnetic article is within the predetermined distance of said Hall element regardless of the polarity of said magnetic article with respect to said Hall element and provides an output signal having a second different value when said magnetic article is not within the predetermined distance of said Hall element regardless of the polarity of said magnetic article with respect to said Hall element.

20. The cellular telephone of claim 19 wherein said comparator comprises:

a first comparator having a first input terminal adapted to receive a first threshold voltage, a second input terminal adapted to receive an input voltage from said Hall element, and an output terminal coupled to an output terminal of said switch; and

a second comparator having a first input terminal adapted to receive the input voltage from said Hall element, a second input terminal adapted to receive a second threshold voltage and an output terminal coupled to an output terminal of said switch.

21. The cellular telephone of claim 20 wherein said first and second comparators are each provide having a means for including hysteresis.

22. The cellular telephone of claim 20 wherein said switch further comprises means for changing a switch point of said first and second comparators.

23. A method of switching in a wireless communication device comprising the steps of:

(a) sensing with a magnetic field sensing element a magnetic field provided by a magnetic article having a first pole region and a second pole region wherein said magnetic article has first magnetic field polarity at the first pole region and a second different magnetic field polarity at the second pole region;

(b) generating a sensor output signal having a signal level which is proportional to the magnetic field sensed in step (a), wherein the sensor output signal has a first signal direction when said first pole region is proximate said magnetic field sensing element and a second opposite signal direction when said second pole region is proximate said magnetic field sensing element;

(c) comprising the sensor output signal to one of first and second threshold signal levels; and

(d) in response to the sensor output signal level reaching or exceeding the one of the first and second threshold signal levels, providing an output signal having a first signal level regardless of the direction of the sensor output signal.

24. The method of claim 23 further comprising the step of:

(e) in response to the sensor output signal having a first signal level which is less than the one of the first and second threshold signal levels, providing an output signal having a second different signal level regardless of the direction of the sensor output signal.

25. The method of claim 24 wherein, in response to the output signal changing from the first signal level to the second different signal level the method further comprises the steps of changing a switch point of a threshold circuit from a first predetermined threshold level to a second predetermined threshold level.

26. The method of claim 25 wherein the absolute value of the first predetermined threshold level is greater than the absolute value of the second predetermined threshold level.