JPS6324268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a common mode voltage removal circuit for Hall elements.

Conventionally, there are constant voltage source methods and constant current source methods as means for applying control current to Hall elements, but since the internal resistance of the Hall element changes depending on temperature and magnetic field strength, it is difficult to use in devices that require high precision. A constant current source method is generally used.

FIG. 1 shows an example of the configuration of a conventional Gaussmeter using a constant current source method. 1 is a Hall element, and a constant current source 2 is connected between its control current terminals 1a and 1b.
are connected. Output terminal 1c of Hall element 1,
As is well known, 1d has a common mode voltage in addition to the signal voltage (Hall output voltage). Here, the common mode voltage is a voltage that appears in the same phase at the two output terminals 1c and 1d due to resistance voltage division between the control current terminals 1a and 1b by the internal resistance of the element. That is, if we consider the case where a DC control current is passed between the control current terminals 1a and 1b in a state of zero magnetic field, the voltage at the terminal 1a becomes V.
Assuming that, a voltage of approximately (1/2) V appears at both the two output terminals 1c and 1d, and this (1/2) V is the common mode voltage referred to here. The Hall output voltage obtained when a control current is passed and a predetermined magnetic field is applied appears as a potential difference between the two output terminals 1c and 1d, so in order to detect this, it is necessary to remove the influence of the above-mentioned common mode voltage. There must be. Therefore, in order to remove the common mode voltage, the output terminals _1c and 1d of the Hall element 1 are connected to a fully differential high input impedance buffer amplifier circuit 3 using two operational amplifiers OP 1 and OP ₂ . The balanced output voltage of the buffer amplifier circuit 3 is led to the meter 5 via a differential input/single output type differential amplifier circuit 4 using an operational amplifier _OP3 .

In this case, a high CMMR ( Common Mode R
In order to obtain the ejection ratio ( common-mode component rejection ratio), the resistors R ₁ to R ₄ must satisfy R ₁ ·R ₄ =R ₂ ·R ₃ . For this purpose, it is necessary to make these resistors adjustable as variable resistors or to use highly accurate resistors.

As described above, conventional devices using Hall elements require a fairly complicated circuit to perform high-precision measurements, and also have the disadvantage that the entire device is expensive because it requires variable resistors and precision resistors.

In view of the above points, the present invention provides a Hall element device that removes the common mode voltage of the Hall element without using a differential amplifier circuit, makes a device such as a Gauss meter simple and inexpensive, and enables high-precision measurement. It is something to do.

In this invention, when one input terminal of an operational amplifier, which is a high-gain DC amplifier, is grounded, the other input terminal becomes a so-called virtual ground (imaginary ground). One of the two is virtual grounded, and the Hall output voltage is extracted from the other.

A Gaussmeter according to an embodiment of the present invention is shown in FIG. Reference numeral 11 denotes a Hall element, whose first control current terminal 11a is connected to the constant current source 12, and its second control current terminal 11b is connected to the output terminal of the operational amplifier _OP11 . The non-inverting input terminal of the operational amplifier OP ₁₁ is grounded, and the first output terminal 11c of the Hall element 11 is connected to the inverting input terminal. Then, the Hall output voltage obtained from the second output terminal 11d of the Hall element 11 is transferred to the operational amplifier OP ₁₂ and the resistor.
The signal is led to a meter 14 via a non-inverting amplifier circuit 13 consisting of R ₁₁ and R ₁₂ .

With such a configuration, the current flowing from the constant current source 12 flows into the Hall element 11 as a control current, and then is sucked into the operational amplifier OP ₁₁ .
Since the non-inverting input terminal of operational amplifier OP ₁₁ is at ground potential, the inverting input terminal also becomes virtual ground.
Therefore, the first output terminal 11c of the Hall element 11 also becomes the ground potential. In this way, the second
Since only the Hall output voltage from which the in-phase component has been automatically removed is obtained from the output terminal 11d of the output terminal 11d, it can be extracted by the ordinary non-inverting amplifier circuit 13. Incidentally, if the first output terminal 11c is not virtually grounded but actually grounded together with the control current terminal 11b, a current path is formed between the control current terminal 11a and the output terminal 11c. Formation of such a current path means that the magnitude of the control current that contributes to the Hall effect between the two control current terminals becomes unknown, and that the output terminals 11c and 11d
In addition to the Hall output voltage, a voltage drop due to a lateral current is superimposed between the two, which is extremely inconvenient. By using the virtual grounding of the operational amplifier with high input impedance to ground the output terminal 11c only in terms of potential without causing any current to flow out,
Such inconvenience can be avoided. At this time, considering the case where only the control current flows with zero magnetic field, the potential of the first output terminal 11c is zero, which means that the midpoint in the direction of the control current of the element is zero potential, that is, the second This means that the potential of the output terminal 11d is also zero, and the above-mentioned common mode voltage is automatically removed.

Therefore, according to the present invention, such effects can be obtained.

(1) Since one output terminal of the Hall element is placed in a virtual ground state, the common mode component can be automatically removed without using a differential amplifier circuit, and the circuit configuration is therefore simplified.

(2) For the same reason, there is no need to use a variable resistor or precision resistor to remove the common-mode voltage as in the conventional method, making the device inexpensive.

(3) Since the signal voltage is extracted using the ground potential as a reference, the design of the amplifier circuit becomes easier.

(4) Since one output terminal of the Hall element is virtual grounded, when alternating current is used as the control current,
Compared to conventional systems, approximately twice as much control current can flow at the same circuit voltage. In other words, the sensitivity can be approximately doubled.

FIG. 3 shows an embodiment in which the present invention is applied to an AC wattmeter. Parts corresponding to those in FIG. 2 are given the same reference numerals as in FIG. 2. The AC voltage V _L is converted into a current proportional to V _L via a transformer 21 by a current source circuit 22 consisting of an operational amplifier OP ₁₃ and a resistor R ₁₃ , and is supplied to the Hall element 11 as a control current. On the other hand, the load current I _L is converted by the ferrite core 23 into a magnetic field B proportional to its magnitude, and is applied to the Hall element 11 . As a result, the Hall output voltage, that is, the power value proportional to the product of V _L and I _L , is at the output terminal 1.
1d.

As described above, according to the present invention, the common mode voltage of the Hall element can be easily and effectively removed by utilizing the characteristics of an operational amplifier, thereby simplifying the configuration and lowering the cost of various devices using the Hall element. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a Gauss meter using a conventional Hall element, FIG. 2 is a diagram showing the configuration of a Gauss meter according to one embodiment of the present invention, and FIG. 3 is a diagram showing the configuration of a wattmeter according to another embodiment of the present invention. FIG. 11... Hall element, 11a, 11b... Control current terminal, 11c, 11d... Output terminal, 12...
... Constant current source, OP ₁₁ ... Operational amplifier, 13 ... Non-inverting amplifier circuit, 14 ... Meter.

Claims (1)

[Claims] 1. A Hall element having first and second control current terminals for flowing a control current and first and second output terminals for obtaining a Hall voltage, and a Hall element connected to the first control current terminal of this Hall element. a constant current source, an output terminal connected to a second control current terminal of the Hall element, one input terminal connected to the first output terminal of the Hall element, and the other input terminal grounded; A Hall element device comprising: a high gain operational amplifier whose first output terminal is virtually grounded; and an amplifier which detects a Hall voltage, which is connected to a second output terminal of the Hall element.