Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2003-11-13
2004-09-21
LeDynh, Bot (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S207200
Reexamination Certificate
active
06794863
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field sensor, method for detecting magnetic field and device for detecting magnetic field, capable of detecting the strength of a magnetic field without relying to the polarity of the magnetic field.
In recent years, demands for a magnetic field sensor as a position sensor such as open/close detection device or a rotation detection device which are mounted on a miniature electronic machine such as a folding-type cellular phone, a notebook personal computer and a digital still camera are rising. In regard to a magnetic field sensor which is to be mounted on a portable miniature electronic machine, its circuit scale and electric current consumption needs to be both reduced.
Generally, a magnetic sensor is monolithically integrated and configured by using a bipolar transistor, a CMOS device or the like. Such magnetic sensor has a magnetoelectric element which generates a voltage in proportion to a magnetic field or a magnetic flux density, an amplifier which amplifies the output signal of a magnetoelectric element, and a comparator which compares the output voltage of the amplifier with the pre-determined reference voltage, and outputs the judgment result of whether the strength of the magnetic field detected by the magnetoelectric element (Hereinafter described as “detected magnetic field”) is larger or not compared with the pre-determined strength of the magnetic field. A Hall element which outputs a voltage corresponding to the magnetic field strength or the magnetic flux density which passes through the element, or a magnetic resistance whose resistance value varies according to the strength of the magnetic field is used as a magnetoelectric element.
In order to obtain an accurate comparison result according to the strength of the magnetic field from the magnetic field sensor, there is a need to control the offset signal contained in the signal outputted from the amplifier, and to minimize the dispersion of the signal outputted from the amplifier for each magnetic field sensor (product). There are two major factors for an offset signal to occur. One factor is an offset signal component of a magnetoelectric element due to the effect of a stress of a sealing package or the like, and the other is an input offset signal component of an amplifier.
Method for compensating the offset signal component of a magnetoelectric element is disclosed in the specification of U.S. Pat. No. 4,037,150. More specifically, of the output terminals of the magnetoelectric element having four terminals which are geometrically equal, voltage differences of the two pairs of output terminals located in a diagonal position are outputted, wherein the first phase and the second phase of the synchronizing signal which acts as a trigger for detection is alternately switched, and a sum of the output values is obtained. The effective signal component is doubled since it is in a same phase, and the offset signal component is cancelled since it is in an opposite phase.
One of the factors to determine superiority of a magnetic field sensor is whether a detection of a magnetic field is capable or not, regardless of the polarity of the magnet incorporated to a product, or in other words, corresponding to the magnetic field of both polarities. If a judgment of a magnetic field strength is capable regardless of the polarity of the magnet, controlling the direction of a magnet when placing a magnet in a position sensor or the like incorporating a magnet and a Hall IC, becomes unnecessary.
Hereinafter, a conventional magnetic field sensor judging the magnetic field strength of both polarities disclosed in the Official Gazette of Japanese Unexamined Patent Publication Hei 7-83699 is described in reference to the drawings.
FIG. 4
shows a configuration example of a conventional magnetic field strength judgment circuit of both polarities. As shown in
FIG. 4
, a conventional magnetic field sensor is comprised of a magnetoelectric element (“Hall element” in prior art)
101
, a voltage amplifier
102
which amplifies the output voltage of the magnetoelectric element
101
, a first Schmitt trigger circuit
103
A which receives the output voltage from the voltage-amplifier
102
and outputs a different voltage depending on its threshold value, a second Schmitt trigger circuit
103
B which receives the output voltage from the voltage amplifier, inverting the polarity of the input signal of the first Schmitt trigger circuit
103
A, and a logic latch circuit
104
which receives and latches the output signal from the first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B.
Operation of a conventional magnetic field sensor which is configured as such is described.
First, a Hall voltage which occurs at the output terminal of the magnetoelectric element
101
in proportion to the magnetic flux density passing through the magnetoelectric element
101
is amplified by the amplifier
102
, and an amplified voltage VH is obtained.
Next, the first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B input the amplified voltage VH, compares whether the value of the amplified voltage VH is larger or not than the set voltage value, and outputs the judgment value. The first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B is an equivalent circuit, and by mutually inverting the polarity of the input signal, level detection of the magnetic field strength of the north polarity and the south polarity are performed separately in these two Schmitt trigger circuits
103
A and
103
B.
Then, the output value of the first Schmitt trigger circuit
103
A and the second Schmitt trigger circuit
103
B are inputted to the logic latch circuit
104
. Subsequently, an output value is outputted from the logic latch circuit
104
, wherein a certain computation is performed to the output value of the two Schmitt trigger circuits
103
A and
103
B corresponding to magnetic fields of the north polarity and the south polarity respectively. The output value from the logic latch circuit
104
is a binary value irrelevance to polarity of the detected magnetic field representing whether or not the strength of the detected magnetic field is larger than the strength of the set magnetic field.
However, a conventional magnetic field sensor has a difficulty wherein reducing both the circuit scale and electric current consumption is difficult, since two sets of Schmitt trigger circuit are needed as a voltage comparator circuit in order to detect a magnetic field strength regardless of the polarity of the magnetic field and corresponding to the magnetic field of both polarities.
The present invention has the purpose of providing a magnetic field sensor, a device for detecting magnetic field and a method for detecting magnetic field which solves the above-mentioned conventional problem, detecting a magnetic field strength of both polarities regardless of the polarity of the magnetic field with a simple configuration and consumes a small amount of power.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned difficulties, the present invention has the following configuration. A magnetic field sensor in accordance with the present invention from one aspect is comprised of a first switch part which receives a signal corresponding to a signal of a magnetoelectric element in an applied magnetic field, and which outputs an output signal so that a polarity of the output signal in a first period and a fourth period are each opposite to a polarity of the output signal in a second period and a third period, an amplifier which amplifies the output signal of the first switch part and outputs an output signal to its output terminal pair, a first memory element of which both ends are connected to the above-mentioned output terminal pair of the amplifier, a second switch part connected between one of the above-mentioned output terminal pair and one terminal of the above-mentioned first memory element, and which closes in synchronizati
LeDynh Bot
Matsushta Electric Industrial Co., Ltd.
McDermott Will & Emery LLP
LandOfFree
Magnetic field sensor, method for detecting magnetic field... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic field sensor, method for detecting magnetic field..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic field sensor, method for detecting magnetic field... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3231720