JPS6211034Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a drive circuit that supplies a drive voltage to a Hall element.

Generally, the sensitivity of a Hall element changes depending on the temperature, so some kind of temperature compensation must be performed when using its output voltage. FIG. 1 is a block diagram showing an example of a conventional temperature compensation circuit. In the figure, H is a Hall element, _A1 is an operational amplifier,
R ₁ and R ₂ are resistances. A constant driving voltage E _d is applied to the Hall element H, and its output voltage e _H
is amplified by amplifier _A1 . Here, resistors R ₁ and R ₂ are operational resistances of amplifier A ₁ , and their ratio is
The gain of amplifier _A1 is determined by _R2 / _R1 .

In the temperature compensation circuit configured in this way,
Temperature compensation for Hall sensitivity is performed by varying the temperature coefficients of the operational resistors R ₁ and R ₂ . In other words, the ratio R ₂ /R ₁ of resistors R ₁ and R ₂ changes depending on the temperature, and the gain of amplifier A ₁ changes, so the Hall sensitivity can be compensated by appropriately selecting the direction of this change. Can be done.

However, in such a temperature compensation circuit, temperature compensation of Hall sensitivity is performed using the difference in the temperature coefficient of the operational resistors, so a different type of resistor must be used as the operational resistor. In addition, the Hall element and amplifier circuit can be integrated into an IC.
If the resistors are formed on the same chip using different technologies, the operational resistors must be manufactured using different processes, so it is not easy to obtain a uniform resistance ratio, and the accuracy of the output voltage also decreases.

The present invention eliminates the drawbacks of the conventional device as described above, and creates a Hall element drive circuit with a simple configuration that can obtain a highly accurate and temperature-compensated output voltage without using any special resistors. The purpose is to achieve this goal.

The Hall element drive circuit of the present invention is a semiconductor
By applying a voltage proportional to the difference between the voltage drop at the p-n junction and the reference voltage to the Hall element,
The drive voltage itself has a positive temperature coefficient, and the Hall sensitivity is temperature-compensated in the drive circuit.

FIG. 2 is a block diagram showing an embodiment of the Hall element drive circuit of the present invention. In the figure, H is a Hall element, A ₂ is an amplifier, Q ₁ and Q ₂ are transistors,
R ₃ and R ₄ are resistances. The collector and emitter of the transistor _Q1 are connected to power supplies +Vs and -Vs via resistors _R3 and _R4 , respectively, and a reference voltage V _R with respect to the power supply -Vs is applied to its base. Further, the base of the transistor _Q2 is connected to the collector of the transistor _Q1 , the collector is connected to the power supply -Vs, and the emitter is connected to the power supply +Vs via the Hall element H. The output voltage e _H of the Hall element H is amplified by the amplifier A ₂ .

The operation of the Hall element drive circuit of the present invention configured as described above is as follows. Now, if the base-emitter voltages of transistors Q ₁ and Q ₂ are V _BE1 and V _BE2 and the current amplification factors are hfe ₁ and hfe ₂ , then emitter current I _E1 , collector current I _C1 , and base current flowing through transistor Q ₁ are I _B1 is respectively I _E1 = (V _R − V _BE1 )/R ₀ I _C1 = I _E1 − I _B1 I _B1 = 1/hfe ₁ ·I _C1 . Here, if hfe ₁ ≫1, I _C1 〓I _E1
It is.

Furthermore, if the base current of the transistor Q ₂ is I _B2 , the current I ₄ flowing through the resistor R ₄ is I ₄ = I _C1 - I _B2 , but if hfe ₂ is sufficiently large, I _C1 ≫ I _B2
Therefore, this current I ₄ is approximately equal to I _C1 (=I _E1 ). Therefore, the voltage drop (R ₄ ·I ₄ ) due to the resistor R ₄ is as follows: R ₄ ·I ₄ =R ₄ ·I _E1 =R ₄ /R ₃ ·(V _R −V _BE1 ). Therefore, the drive voltage Ed applied to the Hall element H is equal to the voltage drop across the resistor _R4 ( _R4・
It is obtained by subtracting the base-emitter voltage V _BE2 of the transistor Q ₂ from I _E1 ), and is expressed as the following equation.

E _d = R ₄ /R ₃ (V _R −V _BE1 )−V _BE2 Here, the base-emitter voltages V _BE1 and V _BE2 of transistors Q ₁ and Q ₂ change with a negative temperature coefficient. Therefore, the magnitude of the reference voltage _VR is relative to the base-emitter voltages V _BE1 and V _BE2 ,
Assuming that V _R >V _BE1 and R ₄ /R ₃ (V _R −V _BE1 )≫V _BE2 , the drive voltage E _d shown in the above equation becomes a voltage with a positive temperature coefficient. Therefore, the reference voltage V _R
By adjusting the magnitude of and making the drive voltage E _d and the temperature coefficient of the Hall element H the same, temperature compensation of Hall sensitivity can be performed.

Furthermore, since the resistors R ₃ and R ₄ used in the drive circuit of the Hall element of the present invention are resistors with uniform characteristics such as temperature coefficient, they can be formed in the same process, and manufacturing is easy. At the same time, a highly accurate output voltage can be obtained. In addition, the Hall element H
Since the output voltage e _H of the amplifier A2 is temperature compensated and is always at a high level without being affected by temperature changes, the relative influence of the offset voltage on the amplifier _A2 can be reduced.

Note that in the above explanation, in order to obtain the drive voltage E _d with a positive temperature coefficient, the transistor
The case where the pn junction between the base and emitter of Q ₁ is used is shown as an example, but it is also possible to use a diode in addition to the transistor, and to amplify the difference between the voltage drop across this diode and the reference voltage and apply it to the Hall element. Even if configured, the same operation can be performed.

As explained above, in the Hall element drive circuit of the present invention, a voltage proportional to the difference between the voltage drop at the pn junction of the semiconductor and the reference voltage is applied to the Hall element. It is possible to realize a Hall element drive circuit with a simple configuration that can temperature-compensate Hall sensitivity and obtain a highly accurate and temperature-compensated output voltage without using special resistors. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional temperature compensation circuit, and FIG. 2 is a block diagram showing an embodiment of a Hall element drive circuit of the present invention. H...Hall element, _A1 , _A2 ...Amplifier, _Q1 ,
Q ₂ ...transistor, R ₁ to R ₄ ...resistance.

Claims (1)

[Scope of utility model registration request] A Hall element, an amplifier for amplifying the output voltage of the Hall element, and a first transistor whose base is applied with a reference voltage and whose collector and emitter are connected to positive and negative power supplies via resistors, respectively.
and a second transistor whose base is connected to the collector of the first transistor and whose collector and emitter are connected between positive and negative power supplies via the Hall element inserted into the emitter side. A Hall element drive circuit.