CA2562985C - Magnetic pole insensitive switch circuit - Google Patents

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 magnet, and hence a magnetic field, to the Hall effect sensor regardless of the orientation of the magnet to the Hall effect sensor.

Description

MAGNETIC POLE INSENSITIVE SWITCH CIRCUIT

This application is a divisional application of Canadian Serial No. 2,343,409 filed September 3, 1999.

FIELD OF THE INVENTION

The present invention relates to switches and more particularly to switches which are responsive to magnet fields.

BACKGROUND OF THE INVENTION

As is known in the art, there exists a relatively large number of commercially available devices having a base or stationary portion and a movable cover or door portion which include a magnet. For example, telephones, cellular telephones, notebook or laptop computers and refrigerators include magnets in the moveable door or cover portions. The covers are typically opened and closed and, in some cases, the magnets provide a magnetic force which maintains the cover or door in a particular position (e.g. a closed position).

Such devices can also include detectors or sensors which indicate when a door or cover is in an open or a closed position. For example, cellular telephones (cell phones) which are provided as so-called "flip phones," include a base and a cover or "flip"
portion. The cover has a magnet disposed therein. Disposed in the base portion of the cell phone is a sensor..
When the cover is closed, the magnet is disposed over the sensor and the sensor detects the pnesience of the magnet's magnetic field. In response to the magnetic field, the sensor provides a signal which indicates that the cover is closed. Similarly, when the cover is open, the magnet (and hence the magnetic field) is removed from the sensor and the sensor provides a signal indicating that the cover is open.

In some applications, the sensor is provided as a Reed switch. The Reed switch is a mechanical type switch comprised of an evacuated glass tube having a series of metal fingers disposed therein. In response to the presence a magnetic field, the metal fingers are in mechanical contact thus providing a signal path having a short circuit impedance characteristic between the input and output terminals of the switch. Likewise, in the absence of a magnetic field, the mechanical fingers are not in contact thus providing a signal path having an open circuit impedance characteristic between the input and output terminals of the switch.

2 Reed switches have 'the advantage that the switch operates regardless of the orientation of the magnet with respect to the switch. That is the Reed switch need not be oriented in a particular manner with respect to the poles of the magnet. This allows for easy replacement of the magnet or the Reed switch since there is no: physical relationship between them.

One problwn with the Reed switch approach, however, is that the Reed switch is relatively large and expensive when compared with semi-conductor type switches. Also, the Reed switch is a mechanical type switch and thus is not as reliable as a solid state device.

SUMMARY OF THE INVENTION

In view of the above problems -with the prior art approach it has, in accordance with the present invention, been .recognized that it would be desirable to provide a replacement for mechanical type- switches such as Reed switches.

One problem with using a semiconductor switch in place of the Reed switch, however is that semiconductor devices, -which include elements such as a Hall element, must be aligned in a particular manner with respect to the north and south poles of the magnet. If the magnet and Hall element are not properly oriented (i.e. the appropriate ends of the Hall element are not aligned with the appropriate magnetic.poles) then the semiconductor switch will not operate correctly. This leads to difficulties when it becomes necessary to replace the magnet or the semiconductor switch. For example, if a magnet must be replaced and neither the. magnet nor the Hall element or switch are somehow coded.so that it is known which end of the magnet to place at which end of the Hall elem.ent, then it is necessary to proceed by trial and error to determine how to install the repIacement parts.' .

It would, therefore, be desirable to provide a reliable magnetic pole insensitive.switch which can serve as a "drop-in" replacement for mechanical type switches such as Reed switches.

3 It would also be desirable to use a semiconductor switch including a Hall effect element as a drop in replacement for a Reed switch type device, however this requires the Hall element to be insensitive as to whether a north pole or south pole is being sensed.

In accordance with the present invention, a sensor for sensing an article which provides a magnetic fieU Itwludes a magnetic-field-to-voltage transducer for generating at an output thereof 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 a window comparator having an input port coupled to the output port of the 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 a first predetermined distance of the magnetic-field-to-voltage transducer regardless of the polarity of the magnetic field. With this particular arrangement, a drop in replacement for a Reed switch type device which is insensitive as to whether a north pole or south pole is being sensed is provided. By providing the comparator as a window or symmetrical comparator (i.e., a comparator having the same switching point for positive and negative magnetic fields) the sensor operates correctly regardless of the orientation of the magnet relative to the magnetic-field-to-voltage transducer.

.20 In accordance with a further aspect of the present invention, a switch includes a Hall element and a threshold detector circuit having a substantially similar switching point for positive and negative magnetic fields. With this particular arrangement, a switch which utilizes a Hall effect device can operate correctly regardless of the orientation of the magnetic poles with respect to the Hall device. In one embodiment, the threshold circuit is provided as a comparator circuit.

3a In accordance with a further aspect of the present invention, there is provided 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.

In accordance with a further aspect of the present invention, there is provided a device comprising any device or apparatus which uses a magnetic device in conjunction with a movable portion:
a base;
an element movably coupled to said base;
a magnetic article disposed in a selected one of said base and said element;
and a switch disposed in the other one of said base and said element, said switch comprising:
a sensor for sensing the magnetic field of the magnetic article and for generating a first signal having a signal level proportional to a magnetic field of a first polarity and a second signal having an opposite signal level proportional to a magnetic field of a second different polarity; and 3b a comparator coupled to the sensor to receive the first and second signals and to provide an output signal having the same value when said magnetic article is within a predetermined distance of the sensor and the magnetic field of the magnetic article has the first polarity as when the magnetic article is within a predetermined distance of the sensor and the magnetic field of the magnetic article has the second different polarity.

BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features of this invention as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:

4 FIG. 1 is a block diagrain of a cellular. telephone including a magnetic pole insensitive switch in accordance with the present invention;
FIG. 2 is a block diagram of a magnetic pole insensitive switch;
FIG. 3 is a schematic diagram of a comparator;
FIG. 3A is a plot of window comparator input voltage versus output voltage;
FIG. 4 is'.4schematic diagram of a switch circuit utilizing a comparator;
FIG. 4A is a plot of voltage versus magnetic field; and FIG. 5 is a schematic diagram of a switch circtiit including a magnetic-field-to-voltage transducer.

DETAILED DESCRIPTION OF THE INVENTION

The following description sets forth an exemplary embodiment in which the present invention may be used. Specifically, certain reference is made below to a cellular telephone (cell phone) application. It should be understood, however, that the present invention finds use in a wide variety of applications and devices and is not limited to the exemplary embodiment described below. For example, the invention may be used in any device or apparatus which uses a magnetic device in conjunction with a movable portion such as a movable cover or door including cellular and non-cellular telephones, notebook or laptop computers and refrigerators.

Referring now to FIG. 1, a cellular telephone (cell phone) 10 includes a base portion 12 having a first end of a cover 14 movably coupled tliereto. In this particular example, the first end of the cover 14 is movably coupled to the base 12 through a rotatable joint 16. Those of ordinary skill in the art will recognize of course that any coupling device or means which allows the cover 14 to move with respect to base 12 maybe- used in place of rotatable joint 16.
Disposed in the second end of the cover 14 is a inagnetic article 18 such as a magnet.
The magnet 18 has a first pole 18a and a second pole 18b. Depending upon how the magnet 18 is disposed in the cover 14 the first pole 18a may correspond to a north or south pole of the magnet and the second pole 18b will correspond to the other pole of the magnet.

S
Disposed in the base 12 is a semiconductor switch 20 which operates regardless of the orientation of the magnetic poles of magnet 18. One possible embodiment of the switch is described in detail below in conjunction with FIGs. 2-5. Suffice it here to say that switch 20 includes a sensor for sensing the magnetic field of the magnet 18 and a threshold detection circuit or compara.Wr.

The transducer provides a transducer output signal having a signal level which varies depending upon the orientation of the magnet 18 to the sensor. Thus, the transducer generates 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. In one embodiment, the transducer may be provided as a magnetic-field-to-voltage transducer.

Switch 20 also includes a comparator coupled to the transducer to receive the first and second signal voltages and to provide an output signal having a first value when the article is within a first predetermined distance of the magnetic-field-to-voltage transducer regardless of the polarity of the magnetic field. Thus, when the cover 14 is open the magnet 18 is displacW
from the switch 20 and the switch 20 provides a switch signal having a first predetermined signal level regardless of the orientation of the magnet 18 with respect to the switch 20.
Similarly, when the cover 14 is closed the magnet is proximate the switch 20 and the switch 20 provides a switch signal having a second predetermined signal level regardless of the orientation of the magnet 18 with respect to the switch 20.

The signal provided by switch 20 merely indicates whether the cover 14 is open or closed. Thus, when the cover is open, the switch provides a first signal having a first value and when the cover 14 is closed, the switch 20 provides a second signal having a second different value.

The signals provided by the switch 20 are coupled to a control circuit 22. The control circuit.22 implements, or causes to be implemented; certain -functions depending upon the position of the cover 14 (i.e. depending upon whether the cover 14 is open or closed). For, example, when the cover is closed, switch 20 provides a signal to control circuit 22 so indicating and control circuit 22 may cause cell phone 10 to operate in a power saver mode.
Referring now to FIG. 2, the switch 20 is shown to include a Hall effect device 30 coupled to a comparator 32. In accordance with the present invention, the Hall effect device 30 functions with the comparator 32 to provide proper operation regardless of the orientation of the magnet 18 with respect to the Hall effect device 30.

The Hall effect device 30 acts as a magnetic-field-to-voltage transducer which generates at output terminals 31a, 31b a first signal voltage having a first signal voltage level 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. The'comparator 32 receives the signals on terminals 31a, 31 b.

It will be appreciated by those of ordinary sldll in. the art that other magnetic-fteld-to-voltage transducers may be used. As one example,. the Hall effect device 30 may be replaced with a magneto-resistive bridge, including a magneto-resistive 'element and a bridge conf guration, such as a Wheatstone bridge: The magneto-resistive element is a resisdve device, such as a metallic thin film resistor, having a resistance that changes depending on the angle between the flux and the device. More particularly, the magneto-resistive element senses flux parallel to the plane of the device and normal to current flow.

The comparator 32 provides an output signal having a first value when the magnet 18 is within a first predetermined distance of the Hall effect device 30 regardless of the polarity of the magnet 18. The comparator 32 provides an output signal having a second different value when the magnet 18 is not within the first predetermined distance of the transducer 30 regardless of the polarity of the magnet 18. Thus, regardless of whether the second end 18b of magnet 18 , i , . . 7 is a north or a south pole, the switch 20 proYides a signal indicating whether the magnet 18 is proximate the sensor 14, Thus, the switch 20 provides, for example, an indication of whether the cover 14 (FIG. 1) is opened or closed.

Referring now to FIG. 3, a comparator circuit 35 has a plurality of terminals, 35a-35e, and includes first and second comparators 36, 38. The comparator 36 has a first terminal 36a coupled to a first reference voltage V.n, at terminal 35a, a second input terminal .36b coupled to an input voltage V,N at terminal 35b and an output terminal 36c coupled to comparator circuit output terminal 35d where an output voltage Vol,.r is provided. A reference voltage, Vm.F is coupled to terminal 35e and provides a reference voltage to comparators 36, 38.

. , . =
The comparator 38 includes a first input termina138a coupled at input port 35b to the input voltage VIN and a second input terminal, 38b, coupled to a threshold voltage VTL at te,rminal 35c. An output terminal 38c of comparator 38 is coupled to provide the output voltage"VpUT at the output terminal 35d. , In this particular embodiment, comparators .36, 38 are provided having a means for including hysteresis such 'that the reference or threshold voltages V.,H, VTL
can be -represented as V.,,,+ and V.m. and V914 + and VT,,, respectively.. The values V,,.,, V-,,,., V.r,.+, V,L. represent the comparator switch points depending upon the value of the output voltage Vot,T. As indicated in FIG. 3A, once the output voltage Võ11=1- switches (e.g. from a high level to a low level), then the switch point changes from V.,}., to V=n,.. Likewise, once the output voltage Vo,,,. switches from a low level to a high level, then the switch point changes from Vrõ_ to VTH+

As can be seen in FIG. 3A, the same holds true as the input voltage. V,N
assumes negative voltages (i.e, voltage values on the left hand side of the Y-axis in FIG. 3A). That is, once the output voltage Vol,r switches then the switch point changes from -V.n,+ to -V,1, and vice-versa depending upon whether the output is switching from low to high or from high to low.

If the output voltage Voi,l, is high and the input voltage V1N has a value greater than or equal to zero, when the input voltage VIN meets or exceeds the voltage V.,,.,,, the output voltage switches 4,4n a value of V,,;H to Vu,W and the switch point changes from VTõ+ to V.
Thus the value of the output voltage VouT will not switch from V,,;,W to VH,c;H until the input voltage V,r, reaches the value VT.,,.

It should be appreciated that in other einbodiments and applications it may be preferable to utilize comparators which do not have hysteresis and thus switching occurs at a single voltage level, namely V.

In operation, and with reference now to FIG. 3A, the input voltage V1N is generated in response to a magnetic field being provided to and removed from a magnetic field sensing device which senses the magnetic field and provides a corresponding signal in response thereto. As discussed above in conjunction with FIG. 1, such a magnetic field could be provided from the opening and closing of a cover having a magnetic article provided therein.

2 0- If the magnetic field sensing circuit is provided as a Hall device, a signal voltage is provided. Assuming the input voltage VIN is at or near zero volts (i.e. V,,, =
0 volts), the output voltage VoõT is at a first predetermined voltage level V,flGH which may correspond for example to a so-called transistor-transistor-logic (TTL) high voltage level.
In response to a magnetic field, the Hall device provides either a positive or a negative input voltage V, If the input voltage provided by the Hall device moves in a positive direction from zero volts toward the threshold voltage, VT,,, when the threshold voltage meets and/or exceeds the threshold voltage level VTH., then the output voltage Vat,T changes from the predetermined signal level, VHIcH to a second predetermined voltage level Vu~w which may correspond for example to a so-called TTL low voltage level. When the input voltage moves past the threshold voltage V. in a negative-going direction, the output voltage changes from VLDw back to VHIaH.

Likewise, as the input voltage moves in a negative direction from zero volts and reaches and/or exceeds the threshold voltage -V.rL*, -the output voltage Vot,r changes from the first value VH,Gq.tathe second value Vu,W. Similarly, as the input voltage VjN
moves from -V.n,.} and reaches and/or exceeds the voltage level -V=rL., the voltage level then changes from the output voltage level VLOW =to Vxiax ==

Referring now to FIGs. 4 and 4A, a switching circuit 40 includes a sensing and control circuit 44 which includes a magnetic field detection circuit 46 coupled to a comparator circuit 48. Comparator circuiY=48 can include the necessary circuitry (e.g. bias circuits) to provide an appropriate control signal to the control terminal of a switch 50 in response to signals provided from the magnetic field detection circuit 46. In one embodiment, the magnetic field detection circuit 46 may include a Hall element which provides an output voltage signal in response to the presence or absence of a magnetic field. In this-particular embodiment, the output of comparator 48 is fed to the switch'50 through an'optional inverter circuit 51..Inverter circuit 51 is here included. to maintain the consistency between the Iogic implemented by the circuit of FIG.. 4 and the logic implemented by the circuits of FIGs. 3. and 5 in an effort to .20 simplify the corresponding descriptions of each of the figures.

The sensing and control circuit 44 provides a comparator output signal at termina144a to a control terminal 50a of a switch 50. In this embodiment, the switch 50 is shown as a transistor and in particular is shown as a bi-polar junction transistor (BJT).
In this case, the control terminal 50a, corresponds to a base terminal of the switch 50. A
second terminal 50b of the switch 50 is coupled through a resistor 52 to a power supply 54 and to an output terminal 40a. A third transistor terminal 50c is coupled to a first reference potential, here corresponding to ground. It should be noted that although the switch 50 is here shown as a BJT, those of ordinary skill in the art will appreciate that other types of . . ' ' = 10 transistors may also be used. For example, in some embodiments, it may be preferable to use a field effect transistor (FET).

Depending upon the proximity of a magnetic article to the magnetic detection circuit, the output signal provided,at the output terminal 40a has one of a first and a second voltage level. When the-magnetic field detection circuit 46 senses a strong magnetic field (such as would be the case, for example, with the cover 14 in FIG. I in the closed position), the comparator 48 provides a first or high signal voltage at control terminal 50a and thus biases the switch 50 into its conductive state. In its conductive state, the switch 50 provides a signal j. 0 path having a relatively low impedance characteristic between the second and third transistor terminals 50b and 50c and thus causes the output voltage V OUT at the output terminal 40a to be a low voltage.

Similarly, with the cover open, magnetic field detection -circuit 46 senses a relatively.
weak magnetic field and the comparator 48 provides a low signal voltage at the control terminal 50a and thus biases switch 50 into its non-conductive state. In its non-conductive state, the switch 50 provides a signal path having a relatively high impedance characteristic '-between the second and third transistor terminals 50b and 50c and thus causes the output volage VouT at ouput terminal 40a to be a high voltage.

Referring briefly to FIG. 4A, the output voltage VouT vs. the magnetic field strength B is shown: As can, be seen from the plot.of FIG. 4A, when the strength of the magnetic field B reaches an operating point level, Bor the output voltage Vt,l,r maintains a low signal'level and when the magnetic field level reaches a -release point level, BRp, the output voltage VoI,T.
reaches a high signal level- It should thus be noted that the sensing and control circuit.44 in combination with switch 50 provide the appropriate signal levels regardless of whether the magnetic field is -a positive field or a negative field= (i.e., a north or a south pole). Thus, as shown in Tabies I and II balow, the switching circuit 40 provides the correct signal to the control circuit 22 (FIG. 1).

TABLE I

COVER COMPARATOR TRANSISTOR
POSITION OUTPUT STATE VouT
CLOSED LOW ON LOW

OPEN HIGH OFF HIGH
Table I shows that when a magnetic field is detected, the comparator 48 provides a signal which biases the transistor 50 into its conductive state (i.e. the transistor is ON). This results in the signal level of the signal VoI,T being low. Similarly, when no magnetic field is detected, the comparator 48 provides a signal which biases the transistor 50 into its non-conductive state (i.e. the transistor is OFF). This results in the signal level of the signal VoI-T
being high. It should be noted that column of Table I labeled "Comparator Output" refers to the output of the comparator 48 prior to the inverter circuit.

Referring now to FIG. 5, a switch circuit 58 includes a magnetic-field-to-voltage transducer provided from a Hall element circuit 60 and a comparator 62. In this particular embodiment, the Hall element circuit 60 has a pair of outputs connected differentially to a pair of input terminals 62a, 62b of a window comparator 62.

The Hall element 60 is mounted such that the Hall voltage increases or decreases based 2 0 upon the proximity of a magnet (not shown) to the Hall element 60.
Alternatively, the detector circuit of FIG. 4 may be used to detect articles that themselves are magnetized.

The Hall voltage signal is manipulated by the window comparator circuitry 62 to produce an output signal VoUT which provides an indication of whether any magnetic particle is within a predetermined distance of the Hall element 60.

The differential input signal is 6oupled= through a filter arid level shifter circuit 64. it. ' should be appreciated that in an alternative embodiment the filter and level shifter circuit 64 could be provided as part of the Hall element circuit 60 rather than as part of the comparator circuit 62, The appropriately filtered and level shifted signals are coupled from the filter and level shifter circuit'64 to respective ones of differential pair circuits 66a, 66b.

Each of the =differential pair circuits 66a ,or 66b, are provided to accept signals generated by the interaction of Hall circuit 60 with a respective one of the north or south poles of a magnet. 'As shown in Table TT., the relationship of the magnet polarity to the Hall effect device (i.e. the orientation of the north and south magnet pples with -respect to the. Hall device) deternriines the output values provided by each the two differential pair circuits.

The output signals provided by the differential pair circuits 66a, 66b are fed to respective ones of output amplifier stages 68a, 68b. The output amplifier states 68a, 68b convert the differential voltage provided from differential pair circuits 66a, 66b into a single ended voltage which drives the inverter circuit 70. Those of ordinary skill in the art appreciate, however, that inverter circuits can be driven with single or differential lines. Those of ordinary slcill in the art will also appreciate when it is preferable to drive an inverter circuit with differential lines rather than a single line.

2 p= The signals are then fed to an inverter circuit 70 which is coupled to the output port 62c of the comparator 62. Comparator circuit 62 also includes a eircuit 76. which includes a plurality of current sources which provide control signals to differential pair circuits 66a, 66b and to .
output amplifier stages 68a, 68b.

25 A temperature and voltage compensation circuit 80 includes a plurality of current sinks 72a - 72c which allow the comparator 62 to operate properly while withstanding a relatively wide range of voltage and temperature changes. .

13 . . . . .....
This is particularly important in devices, such as cell phones for example, in which the normal operating voltage of the device is relatively low. (to conserve battery power and to operate in a power conservation mode, for example). Such low normal operating voltages combined with varying temperature ranges and variations due to standard manufacturing processes used to fabricate circuits, make, it relatively difficult to maintainswitch points of comparator 62. , To,overcome difficulties, a comparator bias circuit 80 allows the comparator 62 to withstand low voltages which change by plus and minus 20%. To maintain the switch points of comparator 62 fixed over this relatively wide range of voltages, the comparator bias circuit 80 provides compensation signals to comparator 62 to allow the.
comparator 62 to operate over a wide range ofvoltage, temperature.and process variations.

The dash line 81 between the current source 72c and the output terminal 62c indicates that the output controls the current source 72c. A first output level causes current source 72c to produce a relatively low current and,a second different output level causes signal source 72c to produce a relatively high current.

As discussed above in conjunction with FIGs. 3 and 3A and as implemented in the circuit of FIG. .5, if an input voltage from the Hall circuit 60 is equal to zero volts and is increasing in a positive direction, then the output voltage VouT.switches once the voltage level reaches and/or exceeds the threshold voltage Vm., thereby causing the output voltage Vcl,r to go low (i.e. assume a voltage level of V,,ow). Depending upon whether the output voltage Vou.,= is high or low., a differential voltage drop exists across one of the resistors R3 or R4 which are coupled to source 72c. Thus, controlling the current source 72c changes the value which causes the differential voltage drop across either resistor R3 or R4 and causes the switch point to be changed from VTH+ to VTH_ or vice-versa (and similarly causes the switch points to be changed from -VTL+ to -VTL')=

Table II below shows the output signal value VoI,r and the opezation of the differential pair comparator circuits 66a, 66b with respect to the magnetic field characteristics.

TABLE II

MAGNETIC FIELD DIFF. DIFF. COMP.
RELATIVE VIN POLARITY PAIR #1 PAIR #2 OUTPUT VouT
STRENGTH

STRONG SOUTH POSITIVE ON OFF LOW LOW
WEAK SOUTH POSITIVE OFF OFF HIGH HIGH
WEAK NORTH NEGATIVE OFF OFF HIGH HIGH

STRONG NORTH NEGATIVE OFF ON LOW LOW
As noted above the comparator 62 is symmetrical and thus (as illustrated in FIG.
3A) there is the same switching point for positive and negative magnetic fields.

The symmetrical comparator 62 of the present invention provides several advantages including: similar operation for both polarities of a magnet and operation which is independent of power supply voltage.

The comparator 62 and the bias circuit 80 may be implemented as a single integrated circuit to thus provide a relatively compact seiniconductor switch circuit which is magnetic pole insensitive.

Having described preferred embodiments of the invention, one of ordinary -skill in the art will now realize further features and advantages of the invention from the above-described embodiments. It should be understood, therefore, that the foregoing is only illustrative of the principles of the invention and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Accordingly, the invention is not to be limite,d by what has been particularly shown and described, except as indicated by the appended claims.

Claims (9)

WE CLAIM:

1. 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.

2. The cellular telephone of claim 1 further comprising a control circuit coupled to said switch.

3. The cellular telephone of claim 1 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 voltage level 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.

4. The cellular telephone of claim 3 wherein said magnetic-field-to-voltage transducer is a Hall element, and said comparator is a window comparator.

5. The cellular telephone of claim 4 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.

6. The cellular telephone of claim 5 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.

7. The cellular telephone of claim 6 wherein said first and second comparators are each provided with a means for including hysteresis.

8. The cellular telephone of claim 6 wherein said switch further comprises means for changing a switch point of said first and second comparators.

9. A device comprising any device or apparatus which uses a magnetic device in conjunction with a movable portion:
a base;
an element movably coupled to said base;
a magnetic article disposed in a selected one of said base and said element;
and a switch disposed in the other one of said base and said element, said switch comprising:
a sensor for sensing a magnetic field of the magnetic article and for generating a first signal having a signal level proportional to a magnetic field of a first polarity and a second signal having an opposite signal level proportional to a magnetic field of a second different polarity; and a comparator coupled to the sensor to receive the first and second signals and to provide an output signal having the same value when said magnetic article is within a predetermined distance of the sensor and the magnetic field of the magnetic article has the first polarity as when the magnetic article is within a predetermined distance of the sensor and the magnetic field of the magnetic article has the second different polarity.