Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2002-07-10
2004-04-27
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S251000, C324S235000, C324S11700H, C324S207200, C327S185000, C327S205000
Reexamination Certificate
active
06727684
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field sensor capable of detecting an intensity of a magnetic field independently of the polarity of the magnetic field.
In a magnetic field sensor, a voltage is generated between output terminals of a Hall element by the Hall effect in proportion to the density of a magnetic flux passing through the Hall element, the generated voltage is amplified by an amplifier, and whether or not the intensity of the detected magnetic field is greater than a predetermined magnetic field intensity is determined by a comparator, using the amplified signal.
Usually, a magnetic field sensor is produced by monolithically integrating bipolar transistors or CMOS devices. One factor that dictates the performance of a magnetic field sensor product is the scattering in a detection value occurring while the detected magnetic field is converted into a voltage and subjected to a comparison. There are two primary causes of the scattering, one being a Hall element offset signal component, which is caused by, for example, a stress from an encapsulation package, and the other being an input-offset signal component to the amplifier.
A method for compensating for the Hall element offset signal component is shown in U.S. Pat. No. 4,037,150. The method shows a Hall element having geometrically equivalent four terminals, or two pairs of output terminals, the output terminals of each pair opposing each other. The potential differences between one pair of output terminals and between the other pair thereof are output alternately in response to the first phase and the second phase, respectively, of a synchronizing signal that triggers a detection operation, and then the sum of the output values is obtained. In this way, the effective signal value is doubled because the effective signal components are of the same phase, and the offset signal components are canceled out by each other because they are of the opposite phases.
Another factor that determines the performance of a magnetic field sensor product is whether it is capable of a bipolar detection, i.e., detecting a magnetic field irrespective of the polarity of a magnet built in the product. If the magnetic field intensity can be determined irrespective of the polarity of a magnet, it is no longer necessary, in a position sensor, or the like, having a magnet and a Hall IC being built therein, to manage the direction of the magnet when determining the position of the magnet.
FIG. 8
shows a conventional magnetic field sensor disclosed in Japanese Laid-Open Patent Publication No. 7-83699, which is capable of a bipolar determination of a magnetic field intensity.
As illustrated in
FIG. 8
, the conventional magnetic field sensor has a Hall element
101
; a voltage amplifier
102
for amplifying the output voltage from the Hall element
101
; a first Schmitt trigger circuit
103
A for receiving the output voltage from the voltage amplifier
102
and outputting different output voltages based on the threshold value thereof; a second Schmitt trigger circuit
103
B for receiving the output voltage from the voltage amplifier
102
while the polarity thereof is inverted from the polarity of the input signal to the first Schmitt trigger circuit
103
A; and a logic latch circuit
104
for receiving and latching the output signals from the first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B.
First, the voltage amplifier
102
amplifies a Hall voltage that is generated between output terminals of the Hall element
101
in proportion to a density of the magnetic flux passing through the Hall element
101
to obtain an amplified voltage VH.
Then, the amplified voltage VH is input to the first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B, each of which determines whether the value of the amplified voltage VH is greater than a predetermined voltage value so as to output a determination value. The first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B are equivalent to each other, and the detection of a magnetic field intensity level for the north polarity and that for the south polarity are performed separately by using the two Schmitt trigger circuits
103
A and
103
B, with input signals of the opposite polarities, respectively.
The output values of the first and the second Schmitt trigger circuits
103
A and
103
B are input to the logic latch circuit
104
. Then, the logic latch circuit
104
outputs an output value obtained by performing an operation on the output values from the two Schmitt trigger circuits
103
A and
103
B corresponding to a magnetic field intensity for the north polarity and a magnetic field intensity for the south polarity. The output value from the logic latch circuit
104
is a binary value that is irrespective of the polarity and that indicates whether the intensity of the detected magnetic field is greater than that of a predetermined magnetic field.
However, the conventional magnetic field sensor involves difficulties in reducing both the circuit scale and the current consumption thereof because it requires two Schmitt trigger circuits as voltage comparison circuits that perform a bipolar detection of magnetic field intensity irrespective of the polarity of the magnetic field.
SUMMARY OF THE INVENTION
The present invention has its object of solving the problems in the prior art by enabling a bipolar detection of a magnetic field intensity irrespective of the polarity of the magnetic field with a simple configuration and with a reduced current consumption.
In order to achieve the object, the present invention provides a magnetic field sensor in which a switch circuit for inverting the polarity of a Hall voltage is provided in a stage preceding a voltage comparison circuit that compares an amplified Hall voltage with a reference voltage, wherein the voltage comparison circuit inverts the polarity of a hysteresis voltage that determines a reference value of a magnetic field intensity in response to first and second synchronizing signals.
Specifically, a first magnetic field sensor of the present invention includes: a Hall element; a voltage amplifier for amplifying an output voltage from the Hall element so as to output an amplified signal; a voltage comparison circuit for receiving the amplified signal; a switch circuit provided between the voltage amplifier and the voltage comparison circuit for inverting a polarity of the amplified signal; and a latch circuit for holding an output signal from the voltage comparison circuit, wherein the voltage comparison circuit inverts a polarity of a hysteresis voltage that determines a reference value of a magnetic field intensity in response to a first synchronizing signal, which triggers a detection of a magnetic field, and a second synchronizing signal following the first synchronizing signal.
With the first magnetic field sensor, a bipolar voltage comparison can be made with a single voltage comparator irrespective of the polarity of the magnetic field, whereby the magnetic field intensity can be detected with a simple form and with a reduced current consumption.
In the first magnetic field sensor, it is preferable that the latch circuit includes a first flip-flop circuit and a second flip-flop circuit for receiving binary values in response to the first synchronizing signal and the second synchronizing signal, respectively, so as to hold an operated value, which is obtained by an operation on the binary values, in response to the second synchronizing signal as an output value.
A second magnetic field sensor of the present invention includes: a Hall element including two pairs of external terminals; a first switch circuit connected to the two pairs of external terminals for selecting one of the two pairs of external terminals as output terminals; a voltage amplifier for amplifying an output voltage of the Hall element receiving via the first switch circuit and outputting an amplified signal; a memory device for storing the amplified signal; a sec
Le N.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Nguyen Vincent Q.
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