JPH09230015A - Hall element driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the influence of magnetic field dependency of resistance of a Hall element by detecting the voltage between input terminals of a Hall element, and feedbacking a signal amplified in such a manner that the voltage is in an inverse proportion to the magnetic field dependency of resistance of the Hall element as a part of a reference signal of a constant current driving circuit of a Hall element. SOLUTION: A resistance R1 connected to the input terminal side of an operational amplifier 5 uses a resistance between the input terminals of a Hall element equal to the Hall element used in magnetic field measurement. Thus, the magnetic field dependency of the resistance R1 can be made substantially equal to the magnetic field dependency of the resistance R0 of the Hall element. A resistance R2 is a resistor having the temperature dependency approximately equal to that of the resistance R1 . The amplification factor (f) of the amplifier 5 is f=R2 /R1 . As R1 =ag0 , f=R2 /aR0 =bfR00 /R0 , wherein (a) is a constant and (f) and R is constant. Accordingly, if the resistance R2 is suitably selected, the amplification factor (f) can have the relationship of inverse proportion to the resistance R0 of the Hall element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field detection circuit using a Hall element, and more particularly to a Hall element drive circuit capable of temperature correction in a wide magnetic field range.

[0002]

2. Description of the Related Art FIG. 1 shows the principle of a Hall element. When a control current I _{C is} passed between input terminals a and b, it is proportional to a magnetic field B applied to the surface of the Hall element 1 (1). The Hall voltage V _H expressed by the formula appears between the output terminals cd. V _H = KI _C B (1) (K: product sensitivity) By the way, the Hall voltage has a relatively large negative temperature coefficient β, and for example, in the case of a GaAs Hall element, β = −0.0.
It is about 6% / ° C. Therefore, in order to measure the magnetic field accurately, it is necessary to reduce the influence of β by some method. As one of the methods, the temperature dependence of the resistance of the Hall element (in the case of GaAs: temperature coefficient α = + 0.
3% / ° C.) is known. FIG. 2 shows the principle, and the input resistance of the Hall element 1 has a temperature coefficient α and is expressed as R _C = R _O (1 + αΔt). The constant current source 2 obtains an output current I _C proportional to the control voltage V _r , and is expressed by the equation (2). I _C = AV _r A: constant (2) The principle of canceling β tries to decrease because the output of the Hall element has a negative temperature coefficient when the temperature rises, but the voltage applied to the Hall element V _C = I _{Since C} R _C tends to rise due to the positive temperature coefficient of R _C , a part of this rise is fed back to the constant current source, and I _C has a positive temperature coefficient to make β negative. The temperature coefficient is erased.

Specifically, the voltage V applied to the Hall element 1
_C is detected, it is multiplied by f by the amplifier 3, and a constant value V _ro is added by the adder 4 to obtain V _r . V _r = V _ro + fV _C (3) By the way, since V _C = I _C R ₀ (1 + αΔt) (4), the formulas (2), (3), and (4) represent V _r. , V _C
When I _C is obtained by erasing, I _C = I _CO {1-AfR _O (1 + αΔt)} ^-1 (5) Here, it is set that I _CO = AV _ro (6). (5) and rearranging the _{formula, I C = {I CO /} (1-AfR 0)} · {1 / (1- AfR 0 α △ t / (1-AfR 0)} becomes ... (7). If AfR ₀ α △ t / (1-AfR ₀ )) << 1, then (7)
The formula is I _C ≈ {I _CO / (1-AfR ₀ )} · {1 + AfR ₀ αΔt / (1-AfR ₀ ))} (8). Therefore, if the temperature coefficient of I _C is γ, then γ = AfR ₀ α / (1-AfR ₀ ) (9) Since the value of Af can be freely determined, γ = −β can be set. At this time, according to the equation (9), Af = −β / (α−β) R ₀ (10) If Af is given as in the equation (10), the Hall output V _H is V _H = K ₀ I _C B (1 + βΔt) ≈K ₀ I _CO ′ B (1 + βΔt) (1−βΔt) ≈K ₀ I _CO ′ B … (11) Here, I _CO ′ = I _CO / (1-AfR ₀ ) = I _CO · {1 / (1-β / (α−β))} = I _CO (α−β) / (α + 2β) 12) It can be seen from the equation (11) that the temperature coefficient of V _H is canceled in the range of the first-order approximation.

[0004]

The advantages of the above method are as follows.
Since the Hall element itself is a temperature sensor, there is no error in temperature measurement as compared with the method using a separate temperature sensor. However, in this method, although Af is a function of R _{0 in} the equation (10), R ₀ varies depending on the magnetic field B. Therefore, the equation (10) is established only for a specific magnetic field, and the influence of the temperature coefficient β of the Hall voltage cannot be corrected for different magnetic fields. The present invention is to solve the above problems, and in a magnetic field detection circuit using a Hall element, it is possible to correct the temperature of the Hall element in a wide magnetic field range by reducing the influence of the magnetic field dependence of the resistance of the Hall element. The purpose is to

[0005]

According to the present invention, in a circuit for detecting a magnetic field using a Hall element, the voltage between the input terminals of the Hall element is detected and the voltage is inversely proportional to the magnetic field dependence of the resistance of the Hall element. The signal amplified as described above is fed back as a part of the reference signal of the constant current drive circuit of the Hall element.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The principle of the present invention is that in FIG.
The amplification factor f of is not constant but is inversely proportional to the resistance R _{0 of the} Hall element, and the other configurations are the same as those of FIG. Therefore, the amplification factor f of the amplifier 3 in FIG. 2 is set as f = f ₀ · R ₀₀ / R ₀ (13) so as to be inversely proportional to the resistance R _{0 of the} Hall element. However, in the equation (13), f ₀ and R ₀₀ are constant. Therefore, it can be set that AfR ₀ = Af ₀ R ₀₀ = c (constant) (14). Substituting this into the above equation (8), I _C ≈ {I _CO / (1-c)} · {1 + cαΔt / (1-c)} (15) Further, substituting into the above equation (9), I _C temperature coefficient γ
Becomes γ = cα / (1-c) (16), and to set γ = −β, c = β / (α−β) (17) As described above, the temperature coefficient of V _H is canceled in the range of the first-order approximation. Further, at this time, γ represented by the equation (16), that is, −β is constant,
The R ₀ dependency disappears, and there is no magnetic field dependency.

FIG. 3 is a diagram showing an example in which an operational amplifier is used to form an amplifier satisfying the expression (13). In FIG. 3, the resistor R ₁ connected to the input terminal side of the operational amplifier 5 uses the resistance between the input terminals of the Hall element equivalent to the Hall element 1 used for the magnetic field measurement. By doing so, the magnetic field dependence of R ₁ can be made almost equal to the magnetic field dependence of R ₀ . Further, the resistor R ₂ connected between the input and output of the operational amplifier 5 is a resistor having substantially the same temperature dependence as R ₁ . When the resistors are connected in this way, the amplification factor f of the amplifier of FIG. 3 becomes f = R ₂ / R ₁ (18) At this time, R ₁ = aR ₀ (a is a constant), and thus f = R ₂ / aR ₀ = bf ₀ R ₀₀ / R ₀ (b = R ₂ / af ₀ R ₀₀ ) ... (19) Therefore, if R ₂ is appropriately selected, the equation (13) can be satisfied, and the amplification factor can be made inversely proportional to the resistance R _{0 of the} Hall element. Note that R ₂ can also be realized by placing an equivalent Hall element in parallel with the magnetic field. Also, it goes without saying that it should be placed in a place that is as close as possible to R _{1 in} terms of heat.

[0008]

As described above, according to the present invention, in the circuit for canceling the temperature dependency of the Hall element by utilizing the temperature dependency of the electric resistance of the element, the voltage between the input terminals of the Hall element is detected, The voltage amplified in inverse proportion to the magnetic field dependence of the resistance of the Hall element is fed back as a part of the reference signal of the constant current drive circuit of the Hall element, so the magnetic field dependence of the electric resistance of the element is removed. The temperature can be corrected over a wide magnetic field range.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of a Hall element.

FIG. 2 is a diagram illustrating a method of correcting the temperature dependence of the Hall voltage.

FIG. 3 is a diagram illustrating a configuration example of an amplifier.

[Explanation of symbols]

1 ... Hall element, 2 ... constant current source, 3 ... amplifier, 4 ... adder, 5 ... operational amplifier, R _1, R ₂ ... resistance.

Claims (1)

[Claims] 1. A constant current circuit, and a Hall element which receives a current from the constant current circuit and outputs a voltage according to a magnetic field,
It is equipped with an amplifier that amplifies the voltage between the Hall element input terminals, and the output of which is fed back as a part of the reference signal of the constant current circuit, and utilizes the temperature dependence of the resistance between the Hall element input terminals to output the Hall element. In the circuit for canceling the temperature dependency of, the amplification factor of the amplifier is made inversely proportional to the magnetic field dependency of the resistance between the input terminals of the Hall element.