JPH0525203B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an isolator, and particularly to an isolator that insulates a power line between two circuits and transmits signals.

[Prior Art] Conventionally, when transmitting video signals in transformerless devices such as home TVs, it is necessary to insulate the power lines of each device. Furthermore, in digital equipment, such isolation is required when a plurality of equipment is connected for transmission, or when level conversion is required. These devices often use elements such as transformers and photocouplers as isolators.

However, when transmitting a signal containing a wide range of direct current to high frequency components, such as a video signal, through an isolator, a trice cannot be used as an isolator. This is because a transformer cannot transmit DC components, and it is difficult to obtain good frequency and phase characteristics, and if this is done intentionally, the cost tends to be high.

Conventionally, a photocoupler is used for this type of transmission, but when a photocoupler is used as an isolator, a circuit for driving the light emitting diode is required on the primary side, and the power supply for this drive circuit is connected to the secondary side. The drawback is that the configuration is complicated and expensive, such as the need for a power supply circuit for insulation.

[Objective] The present invention has been made in view of the above points, and it is an object of the present invention to provide an isolator that can be constructed simply and inexpensively, has good characteristics, and can perform reliable signal transmission.

[Example] Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

In the present invention, an isolator is configured by first converting an electric signal into a magnetic signal and transmitting it, and then returning it to an electric signal, and the magnetic signal transmission is configured by a magnetic field generating means and a magnetoresistive element.

First Embodiment FIG. 1 shows a schematic diagram of a magnetoresistive element (hereinafter referred to as MR element). In FIG. 1, the reference numeral 1 is a striped ferromagnetic thin film made of permalloy having a thickness of about 500 angstroms, for example, and is formed by a thin film forming method. Two electrodes 1a and 2b are bonded to this ferromagnetic thin film 1 as shown in the figure, and by applying a magnetic field in the direction of the arrow in the figure, changes in the magnetic field are reflected from the electrodes as changes in resistance value. It is something that can be taken out.

Generally, such an MR element has detection characteristics as shown in FIG. In FIG. 2, the horizontal axis shows the strength of the applied magnetic field, and the vertical axis shows the resistance value of the MR element. As shown in the figure, the MR element has a detection characteristic Z in which the resistance value decreases as the magnetic field changes, and there is a part (P -Q).

FIG. 3 shows a first embodiment of an isolator using an MR element as shown above.

In the figure, reference numeral 31 indicates an input signal source that requires insulation, such as an external device output, and a signal from this input signal source 31 is inputted via a terminal 42. The input signal line 12 for generating a magnetic field to be applied to the MR element is connected to this terminal 42. This input signal line 12 is connected via a resistor 22, and the current value applied to the input signal line 12 is determined by this resistor 22.

An MR element 11 is arranged near the input signal line 12, and a predetermined current from a constant current source 21 is applied to this MR element. A bias line 13 is further arranged near the MR element 11, and a constant bias current is applied to this bias line from a constant current source 23, so that the MR element 11 is connected to the center of P-Q. A bias magnetic field is applied using the operating point. The currents applied to these MR elements 11 and bias line 13 are determined according to the characteristics of the MR elements.

The terminals on both sides of the MR element are connected to the inputs of an amplifier 41, and the resistance change across the MR element 11 is taken out as a voltage change, amplified to an appropriate level by the amplifier 41, and output from an output terminal 43. . In order to cancel the DC offset when only a bias magnetic field is applied to the MR element 11, the DC offset of the amplifier 41 is configured to be adjustable by a variable resistor (or semi-fixed resistor) 44.

In the above configuration, when a signal is applied from the input signal line 31, a current determined by the resistor 22 flows through the input signal line 12. This current is input signal source 3
Of course, it changes in response to the voltage of 1.

This current generates a signal magnetic field as shown by the symbol S in FIG. 4 in the input signal line 12 disposed near the MR element 11. Further, a magnetic field corresponding to approximately the midpoint of the portion (P to Q) with good linearity of the characteristic curve of the MR element 11 is applied from the bias line 13 as a bias magnetic field. Therefore, the resistance value change at both ends of the MR element 11 becomes a curve as shown by the symbol R in FIG.

This resistance value change is extracted as a voltage change from both ends of the MR element 11, but since this voltage change is small, it is input to the amplifier 41, and a signal amplified based on a predetermined amplification factor is output from the output terminal 43.

As described above, a signal corresponding to the signal from the input signal source 31 can be obtained at the output terminal 43. Signals are transmitted between the input signal line 12 and the MR element 11 by a magnetic field, and since they are electrically insulated, the above configuration can be suitably used as an isolator.

Second Embodiment In the above-described embodiments, the influence of drift due to the temperature of the MR element is not considered, and the drift of the MR element may cause a large temperature drift in the output. In view of this point, an embodiment as shown in FIG. 5 can be considered.

In Fig. 5, members with the same reference numerals are the third
Since the parts are the same or similar to those in the illustration,
A detailed explanation thereof will be omitted.

In the embodiment of FIG. 5, the signal of the input signal source 31 is
It is applied to input signal lines 12a and 12b connected in series via a resistor 22.

The magnetic fields generated by these input signal lines are thermally coupled to each other, and the MR elements 11 arranged in close proximity are connected to each other.
a, 11b. At this time, the input signal
The MR element is arranged to apply a magnetic field of opposite phase to the MR element. The MR elements 11a, 11b are connected to constant current sources 21a, 21b as in the previous embodiment, and a bias magnetic field is applied from bias lines 13a, 13b arranged nearby. The current applied to the bias line is made constant by constant current circuits 23a and 23b to generate a predetermined bias magnetic field.

The terminal voltages of the MR elements 11a and 11b are input to an amplifier 41 composed of a differential amplifier, and the voltage difference therebetween is amplified and output from an output terminal 43.

In the above configuration, each MR element 11a, 11
The input signal magnetic field and output resistance value changes of b are as shown in FIGS. 6A and 6B. 3A and 3B are diagrams similar to FIG. 4.

That is, as shown in both figures, the MR elements 11a,
Input signal lines 12a, 12b applied to 11b
The signal magnetic fields Sa and Sb generated by are in opposite phase to each other.
A bias line 1 is further connected to the MR elements 11a and 11b.
Bias magnetic fields of the same phase are applied from 3a and 13b, and the resistance value changes Ra and Rb (voltage changes between terminals) of each MR element have opposite phases. As described above, the voltage change of the input signal source 31 is controlled by the MR element 11.
It is extracted in proportion to the voltage difference between terminals a and 11b. This voltage difference is amplified by the amplifier 41, and a signal isolated from the input side can be output from the output terminal to the subsequent stage.

In the above configuration, the MR elements 11a, 11
By thermally coupling b, the MR element 11
The changes in resistance values of a and 11b due to temperature are in the same phase and have the same magnitude. Therefore, the differential amplifier 41 can cancel out temperature drift. Furthermore, by arranging the MR elements 11a and 11b close to each other, the influence of external magnetic fields can be canceled out. That is, although the external magnetic field (noise) acts similarly on each MR element 11a, 11b arranged in close proximity, the resistance value changes of each MR element 11a, 11b caused by this appear in the same phase. Therefore, by extracting the difference in voltage between the terminals of each MR element using the differential amplifier 41, the influence of the external magnetic field can be canceled out.

As described above, a more preferable isolator can be realized.

In the above two embodiments, a conventional photocoupler,
Compared to an isolator using a transformer, this has the advantage that it can be configured more easily because it does not require a drive circuit on the input side, and it can transmit signals with good characteristics from DC components to high frequency components.

In the above two embodiments, the input signal line for applying a signal magnetic field to the MR element is exemplified as a straight line, but it is of course possible to configure it as a coil. Furthermore, although the MR element is constructed from a striped thin film as an example, it goes without saying that other Hall elements may be used. Even more simply, the bias magnetic field may be applied using a permanent magnet. Furthermore, it goes without saying that the resistor disposed at the input in the above embodiments may not be used and may be configured as a current input isolator.

[Effect] As is clear from the above explanation, the present invention employs a configuration in which signal transmission is performed using a magnetic field generating means and a magnetoresistive element, so the configuration is simpler and cheaper than the conventional one. This makes it possible to provide an excellent isolator that can transmit signals with good characteristics from DC components to high frequency components.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a magnetoresistive element used in the present invention, Fig. 2 is a diagram showing the characteristics of the magnetoresistive element shown in Fig. 1, and Fig. 3 explains a first embodiment of the invention. FIG. 4 is a diagram explaining the operation of the circuit in FIG. 3, FIG. 5 is a circuit diagram explaining the second embodiment of the present invention, and FIGS. FIG. 3 is a diagram showing the operation of the circuit. 1...Ferromagnetic thin film, 11, 11a, 11b...
Magnetoresistive element, 12, 12, 12b... input signal line, 13, 13a, 13b... bias line,
31...Input signal source, 41...Amplifier.

Claims (1)

[Scope of Claims] 1. In an isolator that transmits signals by electrically insulating a signal input side circuit and an output side circuit, a magnetic field generating means that generates a magnetic field according to an input signal as an input side circuit; and an output side circuit. a signal extraction means using a magnetoresistive element whose resistance value changes depending on the magnetic field generated by the magnetic field generating means as a side circuit; and applying a bias magnetic field according to the characteristics of the magnetoresistive element to the magnetoresistive element. An isolator comprising bias magnetic field generating means.