JPS63172918A - Offset voltage regulating circuit for magnetic sine encoder - Google Patents

Abstract

PURPOSE:To offer a magnetic sine encoder which has no variation in output voltage by compensating a source voltage by using the source voltage so that variation in offset voltage is canceled when the source voltage varies. CONSTITUTION:Magneto-resistance effect element 3, 4, 6, and 7 constitute bridge sides. A differential amplifier 15 inputs signals of opposite points of the bridge circuit, and amplifies and outputs the differential output. A variable resistor 21 regulates so that the offset voltage of the output voltage e3 is zero. Even if the source voltage varies, the total of offset input voltages to a operational amplifier 15 is zero at all times after the bridge circuit is balanced, so no offset voltage variation appears in the output e3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic sine encoder, and particularly to a magnetic sine encoder, in which a magnetic sensor is constructed in a bridge configuration to obtain an output in the form of a sinusoidal wave with changes in magnetic flux, and the output voltage amplitude and offset voltage are The present invention relates to a magnetic sine encoder that is suitable for maintaining a constant value.

[Prior Art] A magnetic encoder having a structure as shown in FIG. 2 has been used in the past for detecting the amount of rotation using a magnetoresistive element (Japanese Patent Laid-Open No. 50-28989).

1 is designed to be able to rotate with a circumferentially magnetized drum as shown in the figure. 2 is a magnetoresistive element placed opposite the R'fTa portion of the drum. Figure 3 is part 1 of Figure 2.
and 2 are expanded, and 3°4 shows the magnetoresistive element, and 5 shows the magnetization pattern of the drum. As shown in Figure 3(b), the magnetic field strength B corresponds to the magnetization pattern.
is distributed in a sinusoidal manner. However, since the change in resistance of the magnetoresistive element is proportional to the strength of the magnetic field and is not related to whether it is an N pole or an S pole, it depicts the distribution of the magnitude of the magnetic field. If the magnetoresistive elements 3.4 are arranged at an interval of λ/2 relative to the magnetic pole pitch λ, and 3 and 4 are formed into a three-terminal circuit as shown in FIG. 4, the voltage at the intermediate connection point will be ■. changes as shown in Figure 5. However, vco is the power supply voltage, and vo is the output voltage. Since the magnetoresistive elements 3 and 4 are arranged at λ/2 with the rotation angle O of the drum, a resistance change of 3°4 is 180° in electrical angle.
The phase difference becomes , and the amount of change in the magnetic field can be detected as vo.

Two sets of such three terminals are connected as shown in FIG. 6th
In the figure, each side of the bridge circuit section includes magnetoresistive elements 3, 4,
6.7. A comparator 8 was provided on the output side of the bridge side. Furthermore, the output of the potentiometer IO was applied to the negative electrode side of the comparator 8 via the resistor 12. Note that the resistor 11 is an input resistor, and the resistor 9 is a feedback resistor.

As shown in Figure 7, each element 3, 4, 6°7 on the bridge side is λ
They were arranged with a shift of /2. If the output of this bridge circuit is input to comparator 8, the output waveform e as shown in Fig. 8 will be obtained.
, is obtained. However, e is the output of the three terminals composed of elements 3 and 4, e is the output of the three terminals composed of elements 6 and 7, e3 is the output of comparator 8, and the comparator of resistor 9 has hysteresis characteristics. 11.1
2 is a resistor for adjusting offset voltage.

In this way, the conventional magnetic encoder is used as a pulse encoder that outputs a pulse signal as an output.

By the way, the sine wave output e2-8 before pulse shaping. If you attempt to directly amplify and output the analog voltage, the output amplitude of the actual voltage will not be constant due to gap fluctuations and temperature characteristics between the magnetoresistive element and the magnetic drum.

In order to improve this characteristic, it is conceivable to detect amplitude fluctuations and change the power supply voltage to make the output amplitude constant.

That is, when the output amplitude becomes small, vo as shown in FIG. When the output amplitude becomes large, vc
By controlling c to be small, the output amplitude can be kept constant. However, the voltage e shown in FIG.
The offset voltage of 1 and e2 is the magnetoresistive element 3, 4,
6.7 is not necessarily made in a balanced manner, so there are some discrepancies.

Figure 9 shows the power supply voltage■. . This shows how the offset voltage changes depending on the size of VCC.
This shows the case where the number is doubled. Magnetoresistive element 3
and 4, the voltage at A, and the voltage at B between elements 6 and 7. The difference between them becomes the offset voltage eOft.

When VCC doubles, elements 3 and 4 form a voltage C, and elements 6 and 7 form a voltage D, and the difference between them becomes an offset voltage QOfa. eoft is twice the eOft.

In this way, the offset voltage changes in proportion to the power supply voltage vcc.

[Problem to be Solved by the Invention 1] As described above, when the power supply voltage VCC is changed in an attempt to keep the output voltage amplitude constant, there is a drawback that the offset voltage changes.

An object of the present invention is to prevent the output voltage offset from changing even if the power supply voltage is changed.

[Means for Solving the Problems] The above object is achieved by using the power supply voltage to compensate so as to cancel out the change in the offset voltage when the power supply voltage changes.

[Operation] Even if there is a fluctuation in the power supply voltage, the offset voltage is compensated so that it does not change.

[Example] FIG. 10 shows a principle diagram of the present invention. Magnetoresistive element 3
, 4, 6.7 constitute the bridge edge. The differential amplifier (op-amp) 13 inputs the signal of the opposing point of the bridge circuit, amplifies and outputs the differential output. This differential amplifier 13 has a power supply voltage ■. . Take in the power supply voltage vc0
Even if the offset voltage tends to increase due to the increase in the offset voltage, the offset voltage acts as a compensation to cancel out the increase. As a result, the offset voltage of the output of the differential amplifier 13 is
It does not change due to power fluctuations.

An embodiment of the present invention will be described below with reference to FIG.

Elements 3, 4, 6.7 are magnetoresistive elements, 15 is an operational amplifier, 16 to 20 are resistors, and 21 is a variable resistor.

Vo and V are the power supply voltages of the bridge circuit of elements 3, 4, and 6.7. The operational amplifier 15 constitutes a differential amplifier with resistors 16 to 19. In other words, α(ex-
et)=ez. However, α indicates the degree of amplification. The direct current components of el and e are generated to some extent due to the unbalanced resistance of elements 3, 4, and 6.7. This unbalance is sometimes e, )e2, e, < e
Sometimes it's 2.

Therefore, it is necessary to be able to compensate for either situation.

In FIG. 1, in consideration of this, a bias is applied using a resistor 20 so that the offset is always biased to one side. The variable resistor 21 adjusts the offset voltage of the output voltage e to zero. After balancing in this way, even if the power supply voltage changes, the total offset input voltage of the operational amplifier 15 is always zero, so no offset voltage change appears in the output e.

FIG. 11 is a diagram showing another specific embodiment of the present invention. Items with the same symbols as those in Figure 1 indicate the same items. The difference from FIG. 1 is that resistors 22 to 24 are used instead of resistor 20 for applying a bias voltage. After the power supply voltage is divided by resistors 23 and 24, it is input to the operational amplifier 15 by resistor 22. Since the input voltage to resistor 22 is smaller than that of resistor 20 in FIG. 1, the resistance value of resistor 22 is.

It can be made smaller than 20. This is effective when there is a limit to the resistance value.

FIG. 12 is a diagram showing still another specific embodiment of the present invention.

The difference from Fig. 11 is the resistor 22 that applies the bias voltage.
24 except that an inverting amplifier composed of an operational amplifier 25 and resistors 26 to 28 was used. According to this embodiment, since the power supply voltage with the polarity reversed is added to both ends of the variable resistor 21, the input voltage to the resistor 19 can be set to both polarities depending on the way the variable resistor is set. Adjustment is possible even if the way the magnetoresistive element is unbalanced is reversed.

In the above explanation, 3, 4, and 6.7 are made as almost the same resistances, so it is unclear which one will cause the offset voltage to be unbalanced, but one of 3, 4, and 6.7 must be set in advance to increase the amount of unbalance. If you make it so that the offset amount will be only on one side, the bias resistor 20
(Fig. 1), 22 to 24 (Fig. 11), inverting amplifier 25
(Fig. 12) can also be made unnecessary.

FIG. 13 is a diagram showing another example of application of the present invention.

29 is a Hall element, and 30 is an operational amplifier. 31-3
5 is a resistor, and 36 is a variable resistor. operational amplifier 30
and resistors 31 to 34 constitute a differential amplifier.

The internal structure of the Hall element and the mechanism for generating an unbalanced voltage (offset voltage) are basically the same as the bridge configuration of the magnetoresistive element described above.

Although FIG. 13 shows the example of the magnetoresistive element shown in FIG. 1 applied thereto, it is also possible to apply the examples shown in FIGS. 11 and 12.

FIG. 14 shows another example of application of the present invention. 3
7.38 is a resistor, and 39 is a variable resistor.

In this embodiment, the output voltage of the intermediate tap of the variable resistor 39 is inputted to one input terminal of the operational amplifier 15 through the resistor 22. In the application example shown in Figure 11, the output from the variable resistor is input to the tenth input terminal of the operational amplifier, but the first
The offset can be adjusted in the same way as shown in FIG.

FIG. 15 shows still another example of application of the present invention. 40.41 is a variable resistor. In this application,
In the application example of FIG. 14, 37 and 38 are variable resistors, and the offset can be adjusted in the same way.

In the above explanation, a variable resistor is used for 21.36, but trimming may be performed using a thick film resistor or the like.

Furthermore, although a magnetoresistive element was used in the above description, it is clear that the present invention can be applied to anything that undergoes similar changes.

Further, although the magnetized drum has been described as being magnetized on the circumference as shown in FIG. 2, the same applies to a disk type drum in which the side surface of the drum is magnetized and the magnetic sensor is placed opposite to the side surface.

The same applies to linear type magnets that are linearly magnetized.

[Effects of the Invention] According to the present invention, it is possible to suppress changes in offset voltage due to fluctuations in power supply voltage, so there is an effect that a magnetic sine encoder without fluctuations in output voltage can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a specific embodiment of the present invention, FIG. 2 is a diagram showing a schematic structure of a magnetic encoder, and FIG. 3 is a diagram showing the arrangement relationship between the magnetoresistive element of the magnetic encoder and the drum magnetization pattern. 4 is a diagram showing the three-terminal connection of a magnetoresistive element, FIG. 5 is a diagram showing its operation, and FIGS. 6 to 8 are circuits and diagrams of a conventional magnetic pulse encoder. A diagram showing the operation, and FIG. 9 is a diagram explaining the offset voltage. Figure 10 is a diagram showing the principle of the present invention, Figures 11 and 12.
The figures are diagrams showing other specific embodiments of the present invention, Figures 13-
FIG. 15 is a diagram showing another example of application of the present invention. 3.4, 6.7... Magnetoresistive element, 15... Differential amplifier (operational amplifier).

Claims (1)

[Claims] 1. A bridge circuit section consisting of a magnetic pole medium that is alternately and continuously magnetized to NS, a magnetic sensor arranged facing the magnetic pole medium and connected in a bridge configuration, and a bridge output of the bridge circuit section. A magnetic sine encoder comprising: an input differential amplifier; and means for applying the power supply voltage of the bridge circuit section to the differential amplifier in order to cancel the power supply voltage variation of the offset voltage to the differential amplifier. Offset voltage adjustment circuit.