JPS646402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a displacement detection device that has a magnetic scale and a magnetic flux-responsive magnetic head that detects the relative displacement of the magnetic scale. The present invention relates to a magnetic head magnetization compensation circuit which is constructed in such a way that an arbitrarily adjustable direct current, which flows diagonally of the circuit connected to the bridge, flows as a bias current through the windings of the magnetic head in order to cancel the effects.

BACKGROUND TECHNOLOGY AND PROBLEMS In a displacement detection device using a magnetic scale, the magnetic head is used as a method to cancel the magnetization of the magnetic head installed in the magnetic scale or the influence of an external magnetic field and to enable stable reading. Japanese Utility Model Publication No. 56-34242 proposed a method in which a bias current of arbitrary polarity and level is applied to the signal winding of a signal winding, and the magnetic flux generated by the bias current is used to compensate for the effects of magnetization or external magnetic fields. has been done.

FIG. 1 shows a circuit diagram for one channel of a magnetic head magnetization compensation circuit according to this method. As is well known, the magnetic head magnetization compensation circuit consists of two circuits shown in FIG. In the figure, 1 is a magnetic head, 2
is an excitation winding, 3 is a signal winding, 4, 5, and 6 are fixed resistors, and 7 is a variable resistor, and resistors 4 and 6 are equal.
The connection point between the resistors 4 and 5 and the slider 8 of the variable resistor 7 are connected to the signal winding 3 via resistors 9 and 10, respectively, and the DC bias current flowing through the signal winding 3 is changed by moving the slider 8. It is adjusted accordingly. The signal leaving the signal winding 3 is applied to the primary winding of the transformer 12 through a DC cut capacitor 11. 13 is a power supply terminal, and 14 is an output terminal.

In the conventional circuit described above, as is clear from Fig. 1, the potential difference between the output terminals A and B of the bridge circuit is
This bias current is obtained by AV _AB ,
Since the arm of the bridge circuit is composed of a resistor, in order to perform stable readings, that is, to keep the bias current stable, the circuit voltage V applied between the input terminals C and D of the bridge circuit must be _c
In addition to stabilizing the magnetic head, for example, if the bias current and other adjustment parts due to the performance specific to the magnetic head are configured as a head amplifier, separated from the main body of the detection device, and power is supplied from the main body,
It is also necessary to take into account variations in bias current due to variations in circuit voltage _Vc .

Furthermore, if the bias current required to compensate for the effects of magnetization, etc. mentioned above is ΔI _B , the current flowing through each arm of the bridge circuit must be set to a sufficiently large value with respect to the bias current ΔI _B , or the circuit voltage V As _c changes, ΔI _B cannot be guaranteed, which increases the power consumption of the bridge circuit and makes it difficult to ensure optimal load conditions for the magnetic head signal winding.

Moreover, when converting a circuit into an IC, it is not easy to form resistors accurately, and the circuit configuration shown in FIG. 1 itself is not suitable for IC.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the drawbacks of the prior art and to provide a circuit that compensates for the effects of magnetization of a magnetic head or external magnetic fields, which is optimal for attempting to integrate the circuit into an IC.

SUMMARY OF THE INVENTION In order to achieve the above object, a magnetic head magnetization compensation circuit of the type mentioned at the beginning according to the invention is provided, in which all four elements of the circuit connected to the bridge are constant current circuits; The gist is to have one constant current circuit that supplies a constant current and is connected in series to the connected circuit.

A magnetic head magnetization compensation circuit according to a first embodiment of the invention is arranged adjacent to a first element of one arm of the circuit connected to said bridge and adjacent to a first element of said one arm of the other arm. The first element to do this is a constant current circuit through which a current half of the above constant current flows. In the magnetic head magnetization compensation circuit according to the second embodiment of the present invention, the first element of one arm of the circuit connected to the bridge and the first element of the one arm of the other arm are connected to the bridge. non-adjacent second elements are constant current circuits carrying the same current, a second element of one arm of the circuit connected to said bridge and a second element of said one arm of the other arm; The first element not adjacent to is also a constant current circuit passing the same current.

Embodiment FIG. 2 shows the basic circuit configuration of a magnetic head magnetization compensation circuit according to a first embodiment of the present invention. In the figures, reference numbers common to those in FIG. 1 indicate the same parts as corresponding parts in FIG. According to the present invention, the resistors of each component of the bridge circuit in the conventional system are replaced with constant current circuits 16, 17, 18, and 19, and one constant current circuit is also provided at one bridge input terminal. 20 are connected. Second
In the embodiment shown in the figure, two constant current circuits 1 are connected to the lower input terminal D of the bridge circuit.
The two constant current circuits 15 and 17 are connected to the upper input terminal C.
are set to equal current values I. Therefore, the total circuit current is 2I, and the maximum value ΔI _B of the bias current ΔI _B flowing through the signal winding 3 of the magnetic head is
In order to obtain max, it is sufficient to set I=ΔI _B max, which shows that the circuit can be configured with a circuit current twice as large as the maximum value of the required bias current.

FIG. 3 shows the basic circuit configuration according to the second embodiment of the present invention, which can further reduce the circuit current, in which all four constant current circuits are of variable type, and the constant current on each diagonal line is circuits 22 and 25,
The arms 24 and 23 are connected to each other so that they always pass the same current, and the currents flowing through both arms 22 and 23 and 24 and 25 vary differentially with respect to each other. In this embodiment, the total circuit current in the bridge circuit is ΔI _B max, and when integrated into an IC, it is possible to further reduce the power consumption of the circuit.

However, here, I ₁ + I ₂ = 2I, I ₁ − I ₂ = ΔI _B Figure 4 is a specific circuit diagram of the circuit shown in Figure 2 when integrated into an IC, and is different from the conventional example. The resistor-based bridge circuit is replaced with a PNP or NPN transistor, creating a compensation circuit that does not change the bias current due to power supply voltage fluctuations and has no loading effect on the signal winding of the magnetic head. . Q ₁ , Q ₂ , Q ₃ , and Q ₄ are transistors with the same area, and Q ₅ , Q ₆ , and Q ₇ are also transistors with the same area. They each form a constant current circuit, and the current I _BIAS flowing through transistor Q ₁ determines the magnitude of the current I flowing through each of transistors Q ₃ and Q ₄ . Transistors Q ₃ and Q ₄
When a current I flows through transistors Q ₆ and Q ₇
A current I flows through each of them. Transistor Q ₈
The potential difference ΔV _B between the bases of Q ₉ and Q ₉ determines the bias current ΔI _B , and a current of the same magnitude
Flows through a resistor connected between the emitters of _Q9 .

Figure 5 is a specific circuit diagram of the circuit shown in Figure 3 when integrated into an IC.
Q ₁₀ , Q ₁₁ , and Q ₁₂ form one constant current circuit, and I _BIAS determines the magnitude of the current flowing through each of transistors Q ₁₁ and Q ₁₂ . transistor
Q ₂₃ and Q ₂₄ have currents I ₁ and _I 2 , respectively, whose sum is 2I and whose difference is equal to ΔI _B determined by ΔV _B
flows. Transistor Q ₁₇ and transistor
Q ₁₉ also forms a constant current circuit, current I ₁ flows through transistor Q ₁₉ , and the current flowing through transistor Q ₁₅ due to the movement of transistors Q ₁₈ and Q ₁₆ is also I ₁ . Transistors Q ₂₀ , Q ₂₁ ,
Q ₂₂ , Q ₁₃ , Q ₁₄ and transistors Q ₁₉ , Q ₁₈ , Q ₁₇ ,
Since Q ₁₆ and Q ₁₅ are formed completely symmetrically, current I ₂ flows through transistor Q ₂₀ and transistor Q ₁₄ .
flows. Therefore, the current flowing through the signal winding 3 is _ΔIB .

Next, as a method for continuously changing the bias current ΔI _B , in the conventional example, it is obtained by using a variable resistor inserted on one side of the bridge circuit, but in the present invention, the bias current ΔI B is obtained by changing the differential input of the differential amplifier section. As described above, similar results can be achieved by changing the voltage ΔV _B. By the way, when implementing IC implementation, it is necessary to adopt a circuit configuration suitable for IC implementation, and also to take into consideration the fact that there are restrictions on input/output terminals from an exterior perspective. As is well known, a displacement detection device using a magnetic scale requires two sets of magnetic heads, and if the circuit configuration shown in Figure 1 is applied as is to an IC, six input/output terminals are required. Therefore, even if the circuit is devised, at least four input/output terminals are required.

FIG. 6 shows a bias current adjustment circuit according to the present invention, in which the output voltage V _REF of the stabilizing circuit 26 is taken out to the outside as an output pin 27, and
Internally, it is divided by dividing resistors R ₁ and R ₂ and connected to one input terminal of the differential amplifier, that is, transistor Q ₉
is supplied to the base. The other input terminals of the two sets of differential amplifiers are drawn out to the outside as input pins 28 and 29, and are connected to the intermediate taps of the two sets of variable resistors RV ₁ and RV ₂ connected between the reference voltage terminal and the connection terminal. By connecting each channel to , the head bias current can be adjusted independently for each channel. 30 and 31 indicate that they are connected to other channels.

According to this method, the number of required input/output terminals is three, resulting in a more effective configuration for IC implementation.

Effects of the Invention As explained above, according to the present invention, it is possible to configure a bias application circuit that is stable against power supply voltage fluctuations, it is possible to reduce the power consumption of the bridge circuit required for bias application, and it is possible to reduce the power consumption of the bridge circuit required for bias application. The load effect on the wire can be reduced to a negligible level, the output does not decrease, and the circuit is suitable for monolithic IC implementation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for one channel of a conventional magnetic head magnetization compensation circuit, FIG. 2 is a diagram showing the basic circuit configuration of a magnetic head magnetization compensation circuit according to a first embodiment of the present invention, and FIG. The figure shows the second aspect of the present invention.
FIG. 4 is a diagram showing the basic circuit configuration of a magnetic head magnetization compensation circuit according to an embodiment of the present invention, and FIG. 4 is a specific circuit diagram of the circuit shown in FIG. 2 when integrated into an IC.
FIG. 5 is a specific circuit diagram of the circuit shown in FIG. 3 when integrated into an IC, and FIG. 6 is a circuit diagram of a bias current adjustment circuit according to the present invention. 1... Magnetic head, 2... Excitation winding, 3... Signal winding, 13... Power terminal, 14... Output terminal,
15-18... Constant current circuit, 20... Constant current circuit, 21... Differential amplifier, 22-25... Constant current circuit, 26... Stabilization circuit, 27... Output pin,
28, 29...Input pins, _Q1 to _Q24 ...Transistors, _R1 , _R2 ...Resistors forming voltage dividers,
RV ₁ , RV ₂ ... Adjustment variable resistor.

Claims (1)

[Claims] 1. In order to cancel the magnetization of a magnetic flux-responsive magnetic head that detects the amount of relative movement with a magnetic scale or the influence of an external magnetic field, a DC current flowing diagonally in a circuit connected to the bridge is used as a bias current. A constant current circuit was provided as an element of each arm of the circuit connected to the bridge, and one further constant current circuit was connected in series to the circuit connected to the bridge. A magnetic head magnetization compensation circuit characterized by: 2 The first element of one arm of the circuit connected to the bridge and the first element of the other arm adjacent to the first element of the one arm both receive a current that is half of the constant current. A magnetic head magnetization compensation circuit according to claim 1, characterized in that it is a constant current circuit. 3. A constant current circuit in which the first element of one arm of the circuit connected to the bridge and the second element of the other arm, which is not adjacent to the first element of the one arm, conduct the same current. and the second element of one arm of the circuit connected to said bridge and the first element of the other arm not adjacent to the second element of said one arm also carry a constant current carrying the same current. A magnetic head magnetization compensation circuit according to claim 1, which is a circuit.