JPH0863834A - Rotary head type magnetic recorder/reproducer - Google Patents

Abstract

PURPOSE: To obtain optical characteristics at all times by controlling the hysteresis characteristics of a Schmidt trigger circuit externally at a level comparing section for constantly selecting the output of a rotary head having high reproduction level under a special reproduction mode of a VTR. CONSTITUTION: A comparator 9 is provided in order to produce an output alternatively from switching circuits 5, 6, 11 for selecting outputs A1-A4 from a plurality of reproduction heads. The hysteresis characteristics of a Schmidt trigger circuit in the comparator are controlled by converting the value of a constant current supply for the Schmidt trigger circuit, i.e., an external voltage (P4), into a current through a V-I conversion circuit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head type magnetic recording / reproducing apparatus, and more particularly, it has a function of reproducing one of the two rotary heads having a larger reproduction signal level in the special reproduction mode. The present invention relates to a rotary head type magnetic recording / reproducing apparatus having the same.

[0002]

2. Description of the Related Art Recent magnetic recording / reproducing devices (VTRs) are
In order to improve the recording density, it is composed of two magnetic heads A and B as shown in FIG.
The azimuth angles of are set to be different from each other.
In addition, in order to obtain a better reproduction signal during special reproduction in which the magnetic head scans across a plurality of tracks, such as during fast-forward reproduction or slow-motion reproduction, reverse azimuths are provided near the magnetic heads A and B, respectively. Auxiliary heads B ', A'
Is provided, the heads having higher reproduction signal levels among the heads A and B ′ and B and A ′ are sequentially selected and taken out at the time of reproduction.

A magnetic recording / reproducing apparatus having such a structure is disclosed in Japanese Patent Application Laid-Open No. 61-92083, and FIG. 6 shows an example of this selecting circuit.

In FIG. 6, terminals A1, A2, A3, A4
Magnetic heads A, B, A'and B'are connected to the respective heads. Reference numerals 1, 2, 3, 4 are amplifiers, respectively. The outputs of the amplifiers 1, 2 are connected to the first switching circuit 5, and the outputs of the amplifiers 3, 4 are connected to the second switching circuit 6.

The first and second switching circuits 5 and 6 are
It is driven by the switching signal input from the terminal P3.
This switching signal is created in synchronism with the rotational phase of the rotary head, and the outputs of the heads A and B'or A'and B which are in contact with the magnetic tape and are in a reproducing state are respectively output from the third switching circuit 11.
Is applied to the comparator circuit 9 via the amplifiers 7 and 8.
Is configured to be applied to.

The comparison circuit 9 compares the envelopes of the reproduced signals of the heads A and B'or A'and B applied via the amplifiers 7 and 8, and outputs a binary signal corresponding to the magnitude relationship to the terminal P1. Output. The signal output to the terminal P1 is the terminal P
Is applied to the third switching circuit 11 via
As the output of the switching circuit 11, the signal of the higher output level of the outputs of the first and second switching circuits 5 and 6 is output to the terminal B1.

FIG. 7 shows a concrete configuration example of the comparison circuit 9. In FIG. 7, V1 and V2 are output terminals of the amplifiers 7 and 8, 91 and 92 are envelope detection circuits, 93 is a level comparison circuit, and 94 is a Schmitt trigger circuit having a hysteresis characteristic.

The envelope detection circuits 91 and 92 have the same structure, and the emitter follower transistor Q uses the outputs V1 and V2 of the amplifiers 7 and 8 as its base inputs.
1, Q4, constant current sources I1 and I2 serving as operating current sources of these transistors Q1 and Q4, resistors R5, R6, R7, R8 and R9 that define an integration time constant, and an external integration capacitor CA, With CB.

The level comparing circuit 93 also supplies differential transistors Q2 and Q3 which receive the envelope outputs of the envelope detecting circuits 91 and 92 as differential inputs, and a constant current which supplies the operating current of these differential transistors Q2 and Q3. Source I
3 and a collector load resistance R7 of the transistor Q2, and the level comparison output is derived by the load resistance R7.

The Schmitt trigger circuit 94 uses an emitter follower transistor Q5 whose base input is the level comparison output, a constant current source I5 which supplies an operating current of the transistor Q5, and a difference whose base input is the emitter follower output of the transistor Q5. Motion transistors Q6 and Q7
And the collector load resistance R1 of the differential transistor Q6
1 and a constant current source I5 serving as an operating current source for the differential transistors Q6 and Q7.

Further, the Schmitt trigger circuit 94 is
A resistor R2 that determines the hysteresis characteristic and a transistor Q
With the collector current of 7 as input, transistors Q8 and Q9
A current mirror circuit, a resistor R3 for converting the mirror output current of the current mirror circuit into a voltage, and a transistor Q10 for outputting the converted voltage by the resistor R3 from the collector as digital data.
And a collector load resistance R4 of this transistor Q10.

[0012]

The problem here is that the terminals other than the terminals A1 to A4, B1 and C1 to C2 are inside the integrated circuit, and the average signal level input to the terminals A1 to A4 is Model (eg NTSC VTR and PAL)
When different depending on the system VTR), the inconvenience as described with reference to FIGS. 8 and 9 occurs, and a plurality of integrated circuits are required, and external parts must be selected each time due to variations in the integrated circuits.

In FIG. 8, A and B are amplifiers 7 and 8, respectively.
9A and 9B are schematic diagrams of the output waveforms of FIG.
Indicates the envelope detection output.

The Schmitt trigger circuit 94 stabilizes the switching operation in the vicinity of the switching point, so that T1 is set to a predetermined threshold level between the signals A and B.
It has a hysteresis so that it can be switched when the above difference occurs.

Therefore, a switching signal is generated at the point of t1 in FIG. 9A, and the output of the third switching circuit 11 becomes as shown in FIG. 9B. On the other hand, when the average output levels of the amplifiers 7 and 8 are small as shown by A'and B'in the same figure (c), if the level difference (hysteresis width) T1 of the threshold levels is unchanged, switching is performed at the point of t2. A signal is generated, and the output of the third switching circuit 11 becomes as shown in FIG.

As is apparent from the waveforms in FIGS. 2B and 2D, in the case of an input with a small level, the point where the levels of both signals A'and B'are actually switched (the same as in FIG. The point (t2 in FIG. 6C) is delayed as compared with the point t1, and the section having the smaller reproduction signal level is actually used.

The hysteresis width T1 which is the level difference between the threshold levels can be changed by actually adjusting external parts. However, the parts must be selected and adjusted each time in consideration of variations in the integrated circuit.

Considering the threshold level of the Schmitt trigger circuit, when the transistor Q6 is off and the transistor Q7 is on, the threshold level VA is VA = R2.VCC / (R1 + R2) (1) ). In this state, when the input voltage level is reversed and the transistor Q6 is turned on and the transistor Q7 is turned off,
The threshold voltage VB at this time is VB = VCC- (I5 + Ib) .R1 (2). Incidentally, I5 is a current value of the constant current source I5, and Ib is a current flowing toward the resistor R2.

These threshold voltages VA and VB depend on the power source voltage Vcc, and therefore the hysteresis width T1.
Also depends on this power supply voltage Vcc. Therefore, when the power supply voltage fluctuates, the threshold voltage VA,
Not only VB, but also the hysteresis width changes, so that there is a drawback that the switching characteristics of the switching circuit also change.

This switching characteristic is described in Japanese Patent Application Laid-Open No. 61-92.
Although it can be made variable by adjusting external parts as shown in No. 083, the parts must be adjusted each time in consideration of variations in the integrated circuit, as described above.

It is an object of the present invention to provide a rotary head type magnetic recording / reproducing apparatus in which the hysteresis characteristic of the level comparing section can be easily changed only by applying a voltage from the outside.

Another object of the present invention is to provide a rotary head type magnetic recording / reproducing apparatus in which the hysteresis characteristic of the level comparing section can be stably set and varied without depending on the fluctuation of the power supply voltage.

[0023]

A rotary head type magnetic recording / reproducing apparatus according to the present invention comprises a detecting means for detecting reproduced signals of a first magnetic head and a second magnetic head, respectively, to obtain first and second envelopes. Hysteresis characteristic comparison means for comparing the levels of the first and second envelopes to generate a comparison result according to the magnitude, and reproduction signals of the first and second magnetic heads according to the comparison result. And a control means for changing and controlling the hysteresis characteristic of the comparison means according to the value of the voltage supplied from the outside.

[0024]

[Function] In the level comparison circuit having the hysteresis characteristic for level comparison, the hysteresis width and the threshold level are controlled to be changed in accordance with the voltage supplied from the outside, and the external parts are not required, which facilitates the operation. It is possible to control various characteristics.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and the same parts as in FIG. 6 are designated by the same reference numerals. Figure 6
A portion different from the above will be described. A VI conversion circuit 10 is provided to externally control the hysteresis width T1 of the comparison circuit 9 having a hysteresis characteristic, and an arbitrary supply voltage V1 applied to the external terminal P4 is supplied. It is converted into a current, and the hysteresis width T1 of the comparison circuit 9 is converted by this current.
Is controlled.

FIG. 2 is a circuit diagram of a concrete example of the VI converting circuit 10 and the level comparing circuit 9, and the same parts as in FIG. 7 are designated by the same reference numerals. First, the VI conversion circuit 10 includes an input stage buffer circuit including transistors Q15 to Q20 and a constant current source I6, a resistor R12 for deriving a voltage appearing at the base of the transistor Q15 as a current, and a mirror for this current as an input current. In order to generate an output current, it has transistors Q13 and Q14 and a current mirror circuit including resistors R10 and R11.

The mirror output current of the current mirror circuit further includes transistors Q11 and Q12, a resistor R13,
Input to the second current mirror circuit composed of R14,
This mirror output current is the differential constant current I5 of the differential amplifier type Schmitt trigger circuit.

In such a configuration, the base potential VA of the transistor Q7, which is the threshold level of the Schmitt trigger circuit, is expressed as VA = R2Vcc / (R1 + R2) (3) like the equation (1). The base potential of the transistor Q6 is V
When A is exceeded, a current (I5 + Ib) flows through the resistor R1, so that the base potential VB of the transistor Q7 drops to VB = VCC- (I5 + Ib) .R1 (4).

Therefore, by arbitrarily selecting the voltage of the external voltage supply terminal P4, I5 is set and the hysteresis width, which is the hysteresis characteristic of the Schmitt trigger circuit, can be arbitrarily changed.

FIG. 3 shows that the section having a small reproduction signal level is not used by adjusting the external supply voltage (terminal P4) for the input signal having a small average value level to adjust the hysteresis width T2. , The effect becomes clear by comparing the waveform of FIG. 9 (d) with the waveform of FIG. 3 (b).

FIG. 4 is a circuit diagram of another embodiment of the present invention, in which the same parts as those in FIGS. In this example, the hysteresis characteristic can be changed by the voltage supplied from the outside, and the threshold level does not depend on the power supply voltage VCC at all.

In the Schmitt trigger circuit 94 in this case, the base voltage level of the differential amplifier type differential pair transistor Q7 is controlled to be changed according to the supply voltage Vr of the external terminal P4, and the base of the transistor Q7 is controlled. Between resistor R15 and PNP transistor Q2
A series circuit with 2 is provided to apply the external supply voltage Vr to the base of the transistor Q22.

Then, a current mirror circuit (transistors Q8, Q) that is an active load of the transistor Q7.
In addition to 9), a transistor Q21 that constitutes a current mirror circuit together with the transistor Q8 is further provided, and the mirror output current from this transistor Q21 and the output current (Ia) of the further provided constant current source Ia are combined. It is adapted to be supplied to one end of the resistor R15.

In such a structure, the threshold voltage VA when the transistor Q6 is on and the transistor Q7 is off is VA = Vr + VBE + IaR15 (5) Note that VBE is the base-emitter voltage of the transistor Q22.

When the transistor Q6 is turned off and the transistor Q7 is turned on in this state, the threshold voltage VB at that time is VB = Vr + VBE + (I15 + Ia) .R15 (6).

As can be seen from the equations (5) and (6), the hysteresis characteristic is completely independent of the power supply voltage Vcc and shows stable characteristics. The hysteresis width is I15
・ It becomes R15 and becomes constant, and it becomes stable without depending on Vcc.

[0038]

As described above, according to the present invention, the hysteresis characteristic of the Schmitt trigger circuit which is the level comparator can be freely changed by the voltage supplied from the outside.
There is no need for external parts, and there is no need to consider variations in the external parts, and the switching characteristics can be varied very easily.

In particular, in a device in which the power supply voltage fluctuates a lot, the hysteresis characteristic also fluctuates and the characteristic deteriorates. According to the present invention, however, the hysteresis characteristic becomes independent of the power source voltage, and therefore the stability is improved. There is also.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a circuit diagram of a main part of an embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the embodiment of the present invention.

FIG. 4 is a circuit diagram of a main part of another embodiment of the present invention.

FIG. 5 is a plan view showing an arrangement of magnetic heads of a VTR.

FIG. 6 is a block diagram of a re-output switching function in a conventional VTR.

7 is a circuit diagram of a main part of the block of FIG.

FIG. 8 is a diagram for explaining the operation of the blocks in FIG.

FIG. 9 is a diagram for explaining the operation of the blocks in FIG.

[Explanation of symbols]

 1 to 4, 7, 8 amplifier 5, 6, 11 switching circuit 9 comparison circuit 10 VI conversion circuit 91, 92 envelope detection circuit 93 comparison circuit 94 Schmidt trigger circuit

Claims (6)

[Claims] 1. A detection means for detecting the reproduction signals of the first and second magnetic heads respectively to obtain first and second envelopes, and a level comparison of these first and second envelopes to perform the comparison. Hysteresis characteristic comparing means for generating a comparison result according to the magnitude, and the first unit according to the comparison result.
And a switching means for selectively deriving a reproduction signal of the second magnetic head, and a control means for changing and controlling the hysteresis characteristic of the comparison means in accordance with a voltage value supplied from the outside. Rotating head type magnetic recording / reproducing device. 2. The rotary head type magnetic recording / reproducing apparatus according to claim 1, wherein the control means has a hysteresis width control means for changing and controlling the hysteresis width of the comparison means according to the supply voltage value. . 3. The comparing means includes a Schmitt trigger circuit having a constant current source, and the hysteresis width control means converts the supply voltage value into a current, and the constant current source according to the converted current. 3. The rotary head type magnetic recording / reproducing apparatus according to claim 2, further comprising current control means for changing and controlling the current value of the magnetic field. 4. The rotary head type magnetic recording / reproducing apparatus according to claim 1, wherein said control means has a threshold voltage control means for controlling a threshold voltage level of said comparison means according to said supply voltage value. . 5. The comparing means comprises a differential amplifier type Schmitt trigger circuit, a current mirror circuit which inputs one output current of the Schmitt trigger circuit, a constant current source, a current of the constant current source and the current. A resistance element that is supplied to one end with a combined current with the output current of the current mirror circuit to generate one base bias of the differential transistor of the Schmitt trigger circuit, and an application that applies the supply voltage to the other end of the resistance element. 5. The rotary head type magnetic recording / reproducing apparatus according to claim 4, further comprising: 6. The applying means has a base to which the supply voltage is applied, a collector to which a reference voltage is applied, and an emitter to which the other end of the resistance element is connected. Rotary head type magnetic recording / reproducing device.