JPH0216403Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a recording/reproduction switching circuit for a magnetic head circuit which extracts the reproduction output of a magnetic head via a step-up transformer.

This invention is applied, for example, to a recording/reproducing head of a floppy disk. FIGS. 1A and 1B show one example and another example of this recording/reproducing head, respectively. The one shown in FIG. 1A is conventionally known, in which the erasing head 1E and the recording/reproducing head 1RP each have cores 2a, 2b, 3 (indicated by dotted line areas) and ceramics 4, 5a, 5b. It is designed to be pasted together. Erase head 1 is placed above and below gap g ₁ of recording/playback head 1 RP.
The relationship is such that gaps g ₂ and g ₃ of E are located. This is to prevent previous signals from remaining unerased due to track deviation when recording is performed by overwriting. By the way, due to improvements in recording density and miniaturization of disks,
When it is desired to narrow the track width, the bonded structure shown in FIG. 1A is not suitable because the core and ceramic have different coefficients of thermal expansion. For example, when forming 135 tracks per inch instead of the conventional 48 tracks per inch, the track width must be 333μ.
It is said to be as narrow as 130μ.

In FIG. 1B, a recording/reproducing head 1RP and an erasing head 1E are each constructed by slicing a core block in consideration of narrowing the track. Such an integral structure is similar to a video head. Unlike the one shown in Figure 1A, the first
The configuration shown in Figure B can easily realize a narrow track width. However, the depth of the core cannot be made very large, and the number of windings is limited, and the number of windings is limited to about 1/10 of that shown in FIG. 1A.
Therefore, it is necessary to use a step-up transformer to improve the S/N ratio of the reproduced signal.

With regard to recording/reproduction switching when using a step-up transformer, this invention improves the symmetry of the recording current waveform during recording, speeds up the rise time, and improves the recording/reproduction head during reproduction without using any relays. On the other hand, the offset current is prevented from flowing.

An embodiment in which this invention is applied to a magnetic head circuit of a floppy disk will be described below with reference to FIG. A digital signal to be recorded, such as an edge component of an MFM modulated signal, is supplied from a terminal indicated by 6 in FIG. 2 as a clock input to a D flip-flop 7. For example, when the binary code is (11011...), the RZ signal whose rising edge coincides with the edge as shown in FIG. 3A is supplied from the terminal 6, and the RZ signal shown in FIG. and as shown in Figure C
Digital signals which are NRZ signals and which are MFM modulated with mutually opposite polarities appear. This digital signal is connected to the NAND gate 8 as a driver.
Switching transistor 9 via a, 8b
It is supplied to the bases of a and 9b, respectively. The NAND gates 8a, 8b are given a recording/reproduction switching pulse (“1” during recording, “0” during reproduction) from the terminal 10, and only during recording, the transistors 9a, 9b are switched on by the digital signal. A switching operation is performed. This transistor 9
The emitters of transistors a and 9b are grounded, and the primary coil 12a of the step-up transformer 11 is connected between the collector of one transistor and the collector of the other transistor.
and a recording/reproducing head 1RP are connected in series.

Further, a PNP type transistor 15 is provided which is turned on only during recording by supplying a switching pulse to its base via an inverter 13 and a buffer 14. When this transistor 15 is turned on, the power supply voltage applied to the power supply terminal 16 is supplied to the collectors of the transistors 9a and 9b via the resistors 17a and 17b having the same value as the diode, and one of the transistors 9a and 9b is turned on. At times, a recording current determined by the power supply voltage and the values of resistors 17a and 17b is supplied to head 1RP.

Also, a first switching transistor 18 whose collector and emitter are connected to the collectors of the transistors 9a and 9b, and the transistor 1
A resistor 1 of equal value for offset current removal is inserted between the collector and emitter of 8 and ground.
9a and 19b are provided. In this embodiment, a bidirectional LEC transistor with excellent symmetry is used as the transistor 18. This transistor 18 is turned off during recording and turned on during reproduction.

Both ends of the secondary coil 12b of the step-up transformer 11 are connected to the input terminals of a reproducing amplifier 20 having a differential amplifier configuration, and a reproduced digital signal is taken out to its output terminal 21. A resistor 2 is connected between the center tap of the secondary coil 12b and the input terminal of the regenerative amplifier 20.
2 and 23 apply a bias voltage obtained by dividing the power supply voltage. This secondary coil 12
A second switching transistor 24 is provided whose collector and emitter are respectively connected to both ends of the transistor b. This transistor 24 is turned on during recording by supplying a switching pulse via the inverters 13 and 25 to its base, and short-circuits both ends of the secondary coil 12b.

In the above configuration, during recording, the switching transistor 18 is turned off and the switching transistor 24 is turned on. Therefore, the recording current in the direction determined by the recording digital signals supplied from the NAND gates 8a and 8b is directed to the head 1.
The signal flows to the RP and is recorded (written) on the magnetic sheet. Since the resistors 17a and 17b and the resistors 19a and 19b have the same size, the rise and fall times of the recording current are the same, and the symmetry of the recording current can be improved. Further, since both ends of the secondary coil 12b of the step-up transformer 11 are short-circuited by the transistor 24, the impedance seen from the primary side can be made extremely small. transistor 24
When the on-resistance of the transformer 11 is R _f and the turns ratio of the step-up transformer 11 is (1:n), the impedance seen from the primary side is (R _f /n ² ). Unlike this idea, it can be set to (1/n ² ) when both ends of the primary coil 12a are short-circuited. By reducing the impedance seen from the primary side, it is possible to prevent deterioration in the rise characteristics of the recording current caused by passing the recording current through the step-up transformer 11.
Further, there is an advantage that the number of turns on the primary side of the step-up transformer can be increased, and the low frequency characteristics during reproduction can be set independently of those during recording.

Also, during reproduction, transistors 15 and 24
is turned off, and the transistor 18 is turned on as a base current flows from the power supply terminal 16 through the resistor. Therefore, the primary coil 12a of the step-up transformer 11 and the recording/reproducing head 1
The RP and the transistor 18 form a closed loop, and the reproduction output is supplied to the reproduction amplifier 20 via the step-up transformer 11. During this reproduction, an offset current is prevented from flowing through the recording/reproducing head 1RP.

As shown in FIG. 4A, if a resistor 19b is simply inserted between the emitter of the transistor 18 and the ground in order to cause the base current _IB to flow, the current IB will flow through the base-collector junction of the transistor 18, as shown by the dashed line. An offset current _IS flows through the primary coil 12a and the head 1RP. This offset current I _S demagnetizes the pattern recorded on the magnetic sheet and causes distortion (asymmetry) in the waveform of the reproduced signal. However, in this idea,
As shown in FIG. 4B, a resistor 19a is also inserted between the collector of the transistor 18 and the ground, and a current I _B ' is caused to flow through the base-collector junction, so that the primary coil 12a and the recording/reproducing head are 1
There is no DC potential difference between both ends of the series connection of RP,
Therefore, it is possible to prevent offset current from flowing. Therefore, demagnetization of the recording signal and distortion of the re-output signal due to the offset current can be prevented.

In the above example, an LEC transistor with good bidirectionality and symmetry is used as the transistor 18, but since the level of the reproduced signal is small, a normal transistor may be used. However, in the case of a normal transistor, the characteristics of the base-emitter junction and the base-collector junction are different, so as shown in Figure 5, one of the resistors, for example 19a, is a semi-fixed resistor, and the offset current is Adjustments will be made so that this does not occur. In this case, since the rise time of the recording current changes due to the difference in the values of the resistors 19a and 19b, the resistors 19a and 19b should be chosen to have as large a value as possible so that their influence on the current can be ignored. It will be done.

As understood from the above description, according to this invention, in a magnetic head circuit using a step-up transformer, switching between recording and reproduction can be performed without using a relay. Therefore, it is possible to eliminate problems such as the need for space for installing a relay, the inability to perform high-speed switching due to relay chatter, and the reduction in reliability due to deterioration of relay contact points. can. Furthermore, during recording, by short-circuiting the secondary coil 12b of the step-up transformer using the second semiconductor switch, the rise characteristics of the recording current can be improved, and the low frequency characteristics during reproduction can be improved. Furthermore, by removing the offset current during reproduction, demagnetization and distortion of the reproduced signal waveform during reproduction can be prevented.

Note that this invention may be applied to recording and reproducing not only digital signals but also analog signals.

[Brief explanation of the drawing]

FIG. 1 is a front view of an example of a recording/reproducing head and a perspective view of another example, FIG. 2 is a connection diagram of an example of this invention, and FIG. 3 is a waveform diagram used to explain a recording signal of an example of this invention. FIG. 4 is a connection diagram used to explain the operation of one example of this invention, and FIG. 5 is a partial connection diagram of another example of this invention. 1RP...recording/reproducing head, 6...recording signal input terminal, 10...recording/reproducing switching pulse supply terminal, 11...step-up transformer, 12a...primary side coil, 12b...secondary side coil, 18, 24...
Switching transistor, 20... Regeneration amplifier.

Claims (1)

[Scope of utility model registration request] a primary coil of a step-up transformer, one end of which is connected to a recording current supply circuit and the other end of which is connected to one end of a recording/reproducing head; a reproducing amplifier connected to both ends of a secondary coil of the step-up transformer; is connected to one end of the primary coil, the other end is connected to the other end of the recording/reproducing head, and is connected to a first semiconductor switch that becomes conductive during reproduction, and both ends of the secondary coil; A second semiconductor switch that becomes conductive during recording is inserted between one end of the first semiconductor switch and a reference potential point, and between the other end of the first semiconductor switch and the reference potential point. a recording/reproducing switching circuit comprising first and second resistors, the other end of the recording/reproducing head being connected to the recording current supply circuit.