JPS583315B2 - Entoujikukenshiyutsusouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cylindrical domain detection device for detecting stray magnetic fields of cylindrical domains in a cylindrical domain holding plate and providing binary signals to utilization circuits.

Conventionally, in a cylindrical magnetic domain detection device using a magnetoresistive sensing element, a change in the electrical resistance of the magnetoresistive sensing element due to a stray magnetic field of the cylindrical magnetic domain is converted into a voltage change by supplying a current to the magnetoresistive sensing element. It was supplying signal amplifiers.

At this time, the magnetoresistive sensing element has a drawback in that it is sensitive to temperature and its electrical resistance changes significantly with changes in temperature.

Therefore, this change in resistance results in a signal level fluctuation, which is extremely inconvenient when determining the second value of the signal.

Therefore, in order to prevent this level fluctuation, conventional cylindrical magnetic domain devices perform capacitive coupling and use a chopper.

This approach has the drawback of increasing the number of circuit elements and also introducing unnecessary noise (for example, chopper switch noise).

The first object of the present invention is to provide a cylindrical magnetic domain detection device which is free from level fluctuations and has a high S/N ratio by using a transformer operated by a current flowing through a magnetoresistive detection element.

A second object of the present invention is to provide an inexpensive cylindrical magnetic domain detection device with a small number of rotating elements.

According to the present invention, there is provided a magnetoresistive detection element that senses a stray magnetic field of a cylindrical magnetic domain, a transformer having a primary coil connected to the magnetoresistive detection element, and a signal amplifier connected to the secondary coil of the transformer. It is possible to obtain a cylindrical magnetic domain detection device including a cloth and a power source that supplies current to the magnetoresistive detection element.

Next, it will be explained in detail using the drawings.

FIG. 1 is a schematic diagram of a conventional cylindrical magnetic domain detection device.

A current is supplied from a current source 1 to the magnetoresistive sensing element 10.11.

A floating magnetic field of a cylindrical magnetic domain is applied to either the magnetoresistive sensing element 10 or 11, causing a change in electrical resistance.

Therefore, the change in resistance causes a change in the voltage between point a and point b.

This voltage change, that is, a signal, is transmitted by capacitors 20 and 21, amplified by signal amplifier 40, and output from terminal 50.

However, since the signal level at the input terminals d and c of the signal amplifier 40 varies depending on the signal waveform, the level is stabilized by the chopper 30.

The chopper 30 has a gate applied to the terminal 60. Driven by pulses.

As can be understood from the above explanation, the magnetoresistive sensing element i
Since the voltage change between a and b caused by the change in electrical resistance due to the temperature change in o and i1 is quasi-static, the capacitor 20
．． 21 can be prevented.

However, the level of the signal occurring between points C and d varies depending on the signal waveform.

For this purpose, the chopper 30 is essential, and a gate for driving the chopper 30 is required. A pulse generation circuit is also required.

As described above, the conventional cylindrical magnetic domain detection device requires a chopper and an associated circuit, which is uneconomical.

In addition, the chopper also generates switching noise, which causes problems in deteriorating the S/N ratio.

FIG. 2 is a schematic diagram of a first embodiment according to the invention.

A transformer 100 is connected to the magnetoresistive sensing element 12 by a power source 2.
Current is supplied through the primary coil of.

When the floating magnetic field of the Ensaku magnetic domain changes the electrical resistance of the magnetoresistive sensing element 12, the current flowing through the primary coil of the transformer 100 also changes. ) occurs.

The signal is amplified by a signal amplifier 41 and sent to an output terminal 51.
You can get more output.

Now, in this device, since the magnetoresistive sensing element 12 and the signal amplifier 41 are coupled by the transformer 100, quasi-static current changes do not induce voltage in the secondary coil.

Therefore, since the change in the electrical resistance of the magnetoresistive sensing element 12 due to temperature change is quasi-static, its influence does not appear on the secondary coil.

Further, since the signal level generated in the secondary coil does not fluctuate, a chopper is not necessary.

If the turns ratio is appropriately selected, the signal amplification in the transformer 100 can be expected.

As can be understood from the above explanation, according to the present invention, the signal level does not fluctuate due to temperature changes, etc., the reliability is high due to the large S/N ratio, and the cylindrical magnetic domain detection device with a small number of circuit elements can be realized. Obtainable.

FIG. 3 is a schematic diagram of a second embodiment of the invention.

This cylindrical magnetic domain detection device uses a transformer 101 in which the primary and secondary coils are tapped at the center.

A power source 3 is connected to the center tap of the primary coil, and current is supplied to the magnetoresistive sensing elements 13 and 14.

A voltage that depends on the difference between the amount of change in the current supplied to magnetoresistive sensing element 13 and the amount of change in current supplied to magnetoresistive sensing element 14 is induced in the secondary coil of transformer 101 .

Therefore, when the magnetoresistive sensing elements 13 and 14 are operated within the same rotating magnetic field, the noise due to the rotating magnetic field becomes an in-phase input to the transformer 101, so it is eliminated or reduced and induced in the secondary coil.

The floating magnetic field of the cylindrical magnetic domain is applied to one of the magnetoresistive sensing elements 13 or 14 at a specific time.

The voltage (signal) generated in this case is induced in the secondary coil without being reduced or eliminated, is amplified by the signal amplifier 42, and is output from the output terminal 52.

Since this second embodiment uses a differential configuration, it is possible to reduce noise caused by rotating magnetic fields and the like.

Furthermore, since the current is supplied from the middle point, no magnetic field is generated due to the steady current, so the transformer can be effectively used without saturating the magnetic core of the transformer with the steady current.

This device also combines the advantages of the device according to the first embodiment.

The above explanation does not provide a detailed explanation of the current supplied to the magnetoresistive sensing element.This may be either a direct current or a pulsed current, and in particular, the pulse width of the bipolar pulsed current may be appropriately adjusted to supply the current to the sensing element. If the signals from both detection elements are supplied to the signal amplifier, the signals from both detection elements can be obtained from the signal amplifier as signals of the same polarity, which is convenient for later waveform processing.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of a conventional cylindrical magnetic domain detection device, with 30
is a chopper, and 40 is a signal increaser. FIG. 2 shows a schematic diagram of a first embodiment according to the invention, 1
00 is a transformer, and 41 is a signal amplifier. FIG. 3 shows a schematic diagram of a second embodiment according to the invention, 1
01 is a transformer, and 42 is a signal amplifier. Note that 1, 2.3 are power supplies, 10, 11, 12,
13 and 14 are magnetoresistive detection elements, respectively.

Claims (1)

[Claims] 1. A magnetoresistive detection element that senses a stray magnetic field of a cylindrical magnetic domain, a transformer in which a primary coil is connected to the magnetoresistive element, and a signal amplifier connected to a secondary coil of the transformer; A cylindrical magnetic domain detection device including a power source that supplies current to the magnetoresistive detection element.