JPS6155793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature compensation circuit for a Hall element so that a constant Hall voltage can be obtained even if the ambient temperature changes.

In conventional Hall element temperature compensation circuits, the Hall coefficient generally decreases as the temperature rises, so in order to obtain a constant Hall voltage regardless of temperature, a negative resistance temperature coefficient is added to the Hall voltage output terminal. Two thermistors are connected in series.

Figure 1 is a block diagram of the circuit, where 1 is a Hall element driven by a constant current power supply 2, 3 is a thermistor for temperature compensation, and 4 is a load resistor between the Hall voltage output terminals of Hall element 1. Temperature compensation of the Hall voltage is performed by the ratio of the sum of the internal resistance Rυ and the resistance value R _L of the load resistor 4 and the resistance value R _S of the thermistor 3. 5 is a differential amplifier, 6
is the output terminal. However, such a temperature compensation method has the disadvantage that the Hall voltage of the Hall element 1 decreases and the noise also increases by about 10 dB compared to the case where the thermistor 3 and load resistor 4 are not connected. In addition, in a temperature compensation circuit using the thermistor 3, the curvature of the temperature equilibrium characteristic curve of the thermistor 3 and the curvature of the temperature equilibrium characteristic curve of the Hall element 1 do not match, so completely flat characteristics cannot be obtained, and the Hall current There is also a drawback that the Hall voltage when applied is about 1.5 dB different from the Hall voltage when a thermal equilibrium state is reached due to Joule heat due to Hall current conduction.

The present invention has been made in view of the above, and includes:
The purpose of this is to ensure that even if the ambient temperature changes, the S/N of the Hall voltage of the Hall element will hardly decrease, and that there will be no difference in the Hall voltage between when a Hall current is applied and when it is in thermal equilibrium. An object of the present invention is to provide a temperature compensation circuit for a Hall element that can compensate the temperature.

A feature of the present invention is that a constant Hall voltage can be obtained even when the ambient temperature changes, and in order to eliminate the difference in Hall voltage between when a Hall current is applied and when the Hall voltage is in thermal equilibrium, the differential amplifier of the Hall voltage output circuit must be Focusing on the fact that the rate of change due to Joule heat due to the output ambient temperature and Hall current energization should be made proportional to the reciprocal of the temperature coefficient of the Hall coefficient, we connected a feedback differential amplifier directly to the Hall voltage output terminal. The voltage between the Hall current terminals was applied to the output terminal of this amplifier through a gain adjuster, and the Hall voltage that changed in response to the difference between the temperature coefficient of the Hall coefficient and the temperature coefficient of the internal resistance between the Hall voltage output terminals was amplified. The second point is that the output due to only this change is canceled out.

The present invention will be explained in detail below using the embodiment shown in FIG.

FIG. 2 is a block diagram showing an embodiment of the Hall element temperature compensation circuit of the present invention. The same parts as in FIG. The difference from FIG. 1 is that the Hall voltage output terminal of the Hall element 1 is input to a differential amplifier 5 having a feedback resistor 7,
The point is that the voltage between the Hall current terminals of the Hall element 1 is applied to the output terminal 6 of the differential amplifier 5 through the gain adjuster 9 after being amplified by the amplifier 8 having a high input impedance.

Now, let R _H be the Hall coefficient when the ambient temperature changes by △T, and R be the internal resistance between the Hall voltage output terminals.
If υ, R _H and Rυ are respectively R _H = R _HO e ^- 〓△ ^T ……(1) Rυ = Rυ _O e ^- 〓△ ^T ……(2) Here, R _HO ; Hall coefficient Rυ _O ; Internal resistance of the Hall voltage output terminal before temperature change α; Temperature coefficient of Hall coefficient β; Indicated by the temperature coefficient of internal resistance between Hall voltage output terminals. By the way, the amplification factor G of the differential ^amplifier 5 having the _feedback resistor 7 connected to the Hall voltage output terminal as shown in FIG. , Hall voltage is Hall current,
When the film thickness of the Hall element and the magnetic field applied to the Hall element are constant, it is proportional to the Hall coefficient, so if the Hall voltage of the Hall element 1 with the characteristics shown by equation (1) is input to the differential amplifier 5. The output voltage _VH changes as shown in the following equation with respect to changes in the ambient temperature ΔT.

20og V _H /V _H o = 20og (β-α)△Toge (dB
) ...(4) Here, if the voltage change between the Hall current terminals when the ambient temperature changes by ΔT is amplified by the amplifier 8 and applied to the output terminal 6 of the differential amplifier 5 through the gain adjuster 9, then −20(β−α)△Toge=−20kβ△
This means that the gain is adjusted by Toge (k is a constant), and an output corresponding to a constant Hall voltage can be obtained from the output terminal 10 of the gain adjuster, regardless of the change in ambient temperature ΔT.

The second
Connect the temperature compensation circuit shown in the figure and set the ambient temperature to 0 to 50.
As a result of measuring the output voltage and output noise generated at the output terminal 10 of the gain adjuster when a Hall current of 30 mA is applied at ℃, both the change in output voltage and the change in output noise in thermal equilibrium state are
It is less than 0.5 dB, which indicates that there is almost no drop in S/N and that good temperature compensation is being performed, with no difference in output between when Hall current is applied and when the thermal equilibrium state is applied.

As explained above, according to the present invention, there is almost no decrease in the S/N of the Hall voltage of the Hall element, and temperature compensation can be performed so that there is no difference in the Hall voltage between when a Hall current is applied and when the thermal equilibrium state is applied. It has a remarkable effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional temperature compensation circuit for a Hall element, and FIG. 2 is a block diagram showing an embodiment of the temperature compensation circuit for a Hall element according to the present invention. 1... Hall element, 5... Differential amplifier, 7...
Feedback resistor, 8...amplifier, 9...gain adjuster.

Claims (1)

[Claims] 1. Has a Hall coefficient of temperature coefficient α, and has a temperature coefficient β
A Hall element having an internal resistance of a current source; a feedback resistor connected between the output terminal of the differential amplifier and a second Hall voltage output terminal; and first and second holes of the Hall element. an amplifier connected between the current terminals and amplifying the voltage generated between the Hall current terminals; 1. A Hall element temperature compensation circuit comprising a gain adjuster that adjusts the gain of an output signal of an amplifier.