Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-02-04
2001-06-26
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207210, C330S00100A
Reexamination Certificate
active
06252395
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an amplification circuit for amplifying a sensing signal of a detecting element. For example, the present invention is preferably applicable to a magnetic rotational position detecting apparatus equipped with a magnetic sensing element, such as a magnetic resistive element or a Hall element, and a signal processing circuit processing the waveform of a tiny signal obtained from this magnetic sensing element.
To detect a rotational speed (i.e., a rotational angle) of an automotive engine, conventional engine speed sensors are equipped with an appropriate magnetic resistive element (MRE). The magnetic resistive element faces a gear fixed to the engine output shaft to detect the directional change of a magnetic field responsive to the rotation of the gear. The detected change of the magnetic field is converted into a tiny electric signal having a sine or sin
3
waveform or a rectangular waveform. A waveform processing circuit amplifies the detected signal and compares the amplified signal with a predetermined threshold, thereby producing a binary signal (i.e., a pulse waveform signal) representing the rotational angle of the gear.
In general, the output value of the magnetic resistive element varies in accordance with temperature change. Thus, the magnetic rotational position detecting apparatus needs to have a temperature compensating function for eliminating adverse influence of the temperature change in the output value of the magnetic resistive element. For example, Unexamined Japanese Patent Application No. Kokai 2-38920 or 5-71980 discloses an operational amplifier with a gain-determining resistor having temperature dependency.
However, the temperature compensation realized by these conventional apparatuses is not satisfactory.
The magnetic resistive element has negative temperature characteristics in its output signal. Thus, the amplitude of the amplified sensor signal reduces with increasing temperature, deteriorating the S/N ratio where the S(signal) component is the output signal of the magnetic resistive element and the N(noise) component is a constant circuit error. The sensor output pulse will have worse accuracy in the angle detection.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an amplification circuit having the capability of producing an output not influenced by the temperature characteristics of the sensing element (i.e., the magnetic resistive element).
In order to accomplish this and other related objects, one aspect of the present invention provides an amplification circuit comprising an operational amplifier for inputting a sensing signal from a temperature-dependent element, a gain-determining input resistor connected to an input terminal of the operational amplifier, and a gain-determining feedback resistor disposed in a feedback path extending from an output terminal of the operational amplifier to the input terminal of the operational amplifier. In this arrangement, the temperature characteristics of the gain-determining input resistor and the gain-determining feedback resistor are opposed to that of the temperature-dependent element, and the gain of the operational amplifier is defined by the gain-determining input resistor and the gain-determining feedback resistor so that the temperature characteristics of the gain can cancel the temperature characteristics of the temperature-dependent element. Thus, it becomes possible to provide the amplification circuit capable of producing an amplified output not influenced by the temperature characteristics of the sensing element
Preferably, the temperature-dependent element is a magnetic detecting element which detects a magnetic field change responsive to the rotation of a rotor and produces an electric signal representing the detected magnetic field change.
Preferably, the gain-determining input resistor and the gain-determining feedback resistor are different from each other in their temperature characteristics.
Preferably, the gain-determining input resistor and the gain-determining feedback resistor are positive in their temperature characteristics.
Preferably, the gain-determining input resistor and the gain-determining feedback resistor are impurity-diffusion resistive elements. More specifically, the operational amplifier is constituted by a MOS process element having a P well region serving as the gain-determining feedback resistor and a P
+
region serving as the gain-determining input resistor. The P well region and the P
+
region are located adjacent to each other in a semiconductor substrate.
Another aspect of the present invention provides a position detecting apparatus comprising a movable member made of a magnetic material and having numerous teeth arrayed along a moving direction, the teeth including at least first teeth and second teeth arrayed at different intervals from each other. A bias magnetic field generating means is provided for generating a bias magnetic field adjacent to the movable member. A magnetic resistive element, disposed between the movable member and the bias magnetic field generating means, detects the direction of the bias magnetic field varying in accordance with the movement of the movable member. An amplification circuit, having two kinds of gain-determining resistive elements, amplifies a sensing signal obtained from the magnetic resistive element. A binary signal producing means is provided for converting an amplified signal produced from the amplification circuit into a binary signal based on a comparison between the amplified signal and a predetermined threshold. In this arrangement, the gain-determining resistive elements have temperature characteristics opposed to that of the magnetic resistive element so that the amplified signal produced from the amplification circuit is not substantially influenced by the temperature characteristics of the magnetic resistive element.
Alternatively, the movable member may have a plurality of teeth sections arrayed along the moving direction with non-edged regions separating the teeth sections, each teeth section including a plurality of teeth arrayed at uniform intervals and each non-edged region being formed into an elongated tooth or a toothless region.
Preferably, the temperature characteristics of the gain-determining resistive elements satisfy a requirement that the amplified signal produced from the amplification circuit has a level processible in the binary signal producing means in an operating temperature range of the position detecting apparatus.
Preferably, the movable member is a rotary member with teeth arrayed along its circumferential periphery.
REFERENCES:
patent: 5493219 (1996-02-01), Makimo
patent: 5637995 (1997-06-01), Izawa
patent: 5841301 (1998-11-01), Horie
patent: 52-187 (1977-05-01), None
patent: 61-209332 (1985-03-01), None
patent: 2-38920 (1990-02-01), None
patent: 5-71980 (1993-03-01), None
patent: 8-338851 (1996-12-01), None
Aoyama Seiki
Makino Yasuaki
Shinoda Takeshi
Denso Corporation
Pillsbury & Winthrop LLP
Snow Walter E.
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