JPH0682445B2 - Magnetic recording / reproducing circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing circuit, and more particularly to improving input conversion noise of a reproducing circuit unit in a magnetic recording / reproducing circuit such as a floppy disk drive.

[Conventional technology]

A conventional magnetic recording / reproducing circuit for a floppy disk having two sets of magnetic heads is shown in FIG. In the figure, WG is a signal indicating a recording state or a reproducing state, SIDE is a signal for selecting a magnetic head, Ha and Hb are magnetic heads respectively, 1 is a control circuit for a center tap circuit, and the WG signal and the SIDE signal In response, the transistors Q ₁ a, Q ₁ b, Q ₂ a, Q ₂ b and the resistors R ₁ a, R ₁ b, R ₂ a, R ₂ b, as well as the center taps 1 a, 1 b
Is to be selected. Also, WR DATA is a recording signal, 2
Is a control circuit for the recording circuit, and Q ₃ and Q ₄ are transistors forming a differential pair for recording.
Are repeatedly turned on and off.
3 is a constant current source for the recording circuit, and Q ₅ is a transistor for determining the value of the current flowing through the transistors Q ₃ and Q ₄ together with the resistor R ₃ .

D ₁ a to D ₁₀ a and D ₁ d to D ₁₀ b are diodes that form a diode matrix switch circuit, and the voltage values under the respective conditions of the center tap terminals 1 a and 1 b, that is, the recording / reproducing and selection side head non- The circuit is controlled in each state by being controlled by the voltage value of each condition of the selection-side head. Each of these diodes on the semiconductor integrated circuit is generally _{D 1 a~D 8 a (D 1} b~D 8 b) are NPN
Transistor collector, base direct connection type, D ₉ a,
_{D 10 a (D 9 b,} D 10 b) the collector of the PNP transistor, are formed in the base direct connection type. The reverse withstand voltage of each diode is about 7V for the NPN structure and about 30V or more for the PNP structure.

Further, 4 is a constant current source for a reproducing circuit, Q ₆ and Q ₇ are transistors controlled by them, R ₄ and R ₅ are resistors, D ₁₁ and D ₁₂ are diodes for preventing a leak current described later, and R ₇ to R ₁₂ is resistance, Q ₉ ,
Q ₁₀ is a transistor pair that constitutes a differential amplifier for reproduction, Q ₈
Is a transistor for determining the value of the current flowing through the differential amplifier together with the resistor R ₆ .

Next, the operation will be described.

First, regarding head selection and switching between recording and playback,
By the control circuit 1 for the center tap circuit which receives the SIDE signal and the WG signal, each transistor Q ₁ a, Q ₁ b, Q ₂ a, Q ₂
It is performed by controlling the on / off of b and the voltage value of the center tap terminals 1a and 1b. Head for example
If Ha is selected, the voltage of the terminal 1a is in recording (power supply voltage Vcc) - during reproduction (Q ₂ a saturation voltage of) the non-operating transistor Q ₁ a, any voltage applied to the (resistor R ₁ a ) - (Q ₂ a of Vbe) become (Vbe is the base emitter voltage). At this time, the voltage of the terminal 1b on the non-selected side becomes 0V.

When the head Hb is selected, the reverse of the above is performed.

Next, at the time of recording, the recording circuit control circuit 2 and the recording circuit constant current source 3 are operated by the WG signal, whereby the transistors Q ₃ and Q ₄ forming a differential pair are mutually connected according to the WR DATA signal. Repeat on and off operations. The current value flowing at this time is a constant current determined by the transistor Q ₅ and the resistor R ₃ as described above. The constant current source 4 for reproduction circuit at the time of recording is set to non-operation, to the connected transistors Q _6, Q _7, Q ₈ to the non-conducting.

Next, the reproducing operation is the reverse of the recording operation, and the reproducing circuit constant current source 4 is operated by the WG signal and the recording circuit constant current source 3 is deactivated. A reproducing circuit for reading recorded data in this case will be described.

The minute playback input signal from the head is fed by the diode D ₉ a (D
₉ b), the transistor through D ₁₀ a (D ₁₀ b) and D _11, D ₁₂
It is input to the differential amplifier composed of Q ₉ and Q ₁₀ , and amplified here. The bias of the circuit is the constant current source of the transistors Q ₆ and Q ₇ , the terminal 1a (1b voltage at the time of reproduction) and the resistors R ₇ and R ₈
Is determined by.

[Problems to be solved by the invention]

In the circuit thus constructed, when the transistor Q ₃ or Q ₄ changes from conducting to non-conducting by the WR DATA signal at the time of recording, the inductance of the magnetic head causes L.
A counter electromotive force of (di / dt) (where i is the current value flowing in the transistor Q ₅ ) is generated at the magnetic head terminal. The value of this back electromotive force becomes a problem especially in the case of a floppy disk device (the value of L is large in the case of a floppy disk), and it changes depending on the values of L and i, and reaches a value several times Vcc. There is. However, when such a back electromotive force is generated at the magnetic head terminal, this causes Vcc to pass through the resistor R ₇ (R ₈ ) and the base → collector → resistor R ₁₁ (R ₁₂ ) of the transistor Q ₉ (Q ₁₀ ). A leak current will flow to Vcc through. So to prevent this, a diode
D ₁₁ and D ₁₂ are provided. This diode
D ₁₁ and D ₁₂ are usually the above-mentioned PNP structure.

As described above, in the conventional magnetic recording / reproducing circuit, the diodes D ₁₁ and D ₁₂ are required to prevent the leakage current, but the diodes D ₁₁ and D ₁₂ are provided. This increases the base resistance of the transistors Q ₉ and Q ₁₀ . Therefore, the input conversion noise of the differential amplifier of the reproducing circuit becomes large, the recording / reproducing performance deteriorates, and there is a problem that, for example, a weak signal cannot be reproduced.

The present invention has been made in view of the above points, and an object thereof is to obtain a magnetic recording / reproducing circuit capable of improving the input conversion noise of the differential amplifier in the reproducing circuit section.

Now, the conventional circuit will be examined in more detail. now,
Considering a differential amplifier as shown in FIG. 3, generally, the equivalent input noise eni of the differential amplifier is Rb 'is a base spreading resistance of the amplification stage NPN transistor, and normally rb' of the NPN transistor is about several Ω. Also, Δf is the signal bandwidth, Re is a transistor
The emitter resistance of Tr itself, β is the current amplification degree.

The above-mentioned rb 'is equivalently equivalent to (D ₉ a operating resistance) + (D ₁₁ operating resistance) + (Q ₉ base spreading resistance) in the conventional reproducing circuit shown in FIG. . The operating resistance when a current of 100 μA is applied to the diodes D ₉ a and D ₁₁ is (q / kT) / 100 μA ≈ 260 Ω. Moreover, the base spreading resistance of an NPN transistor is usually about several Ω.

From the above, it is possible to reduce the equivalent input noise by reducing rb ′ in the above formula of eni, and therefore, the diodes D ₁₁ and D ₁₂ in the conventional example are prevented while preventing the leak current by the back electromotive force by some means. It is conceivable that the input-equivalent noise level of this reproducing circuit can be reduced by eliminating the above.

[Means for solving problems]

Therefore, in the magnetic recording / reproducing circuit according to the present invention, the diode connected to the base of the conventional amplifying transistor is deleted, and a leakage current is prevented between the collector of the amplifying transistor and the load resistor connected to the power supply path. It is provided with a diode.

[Action]

In the present invention, the number of diodes connected to the base of the amplifying transistor is reduced and the equivalent input resistance is reduced, so that the input conversion noise of the reproducing circuit is reduced.

〔Example〕

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

FIG. 1 shows the configuration of a magnetic recording / reproducing circuit according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 2 indicate the same elements. In this embodiment, the leakage current preventing diodes D ₁₁ and D ₁₂ and the resistors R ₇ and R ₈ in the conventional example are deleted, and the NPN transistors Q ₉ and Q ₁₀ and the load resistors R ₁₁ and R ₁₂ in the regeneration circuit amplification stage are deleted.
Leakage current prevention diodes D ₁₃ and D ₁₄ are inserted between and. That is, the cathodes of the diodes D ₁₃ and D ₁₄ are connected to the transistors Q ₉ and Q ₁₀ side, and the anodes are connected to the load resistance side. And these diodes usually use the above-mentioned PNP structure. The reproduction output is taken out from the connection point between the load resistance R ₁₁ (R ₁₂ ) and the anode of the diode D ₁₃ (D ₁₄ ).

With such a configuration, the number of diodes connected in series to the base of the NPN transistor in the amplification stage is one, and the equivalent input resistance is small. Therefore, r in the above eni formula
b'becomes smaller and the input conversion noise of the reproducing circuit can be reduced. During recording, the transistor
The constant current circuit of Q ₆ , Q ₇ , and Q ₈ is inactive, and no leak occurs from this path.

In the above embodiment, the case of two sets of magnetic heads has been described, but the present invention can be applied to the case of having a plurality of sets of magnetic heads, and the same effect as that of the above embodiments can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the leakage current preventing diode connected to the base of the conventional amplifying transistor is deleted, and the diode is connected between the collector of the amplifying transistor and the load resistor connected to the power supply path. Therefore, it is possible to reduce the noise of the reproduction amplifier during reproduction while preventing the leak current due to the back electromotive force generated in the magnetic head during recording.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic recording / reproducing circuit according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional magnetic recording / reproducing circuit, and FIG.
The figure is a circuit diagram for explaining equivalent input noise of a differential amplifier. Ha, Hb ...... Magnetic head, Q ₃ , Q ₄ ...... Recording circuit amplification transistor, Q ₉ , Q ₁₀ ...... Reproduction circuit amplification transistor,
R ₁₁ , R ₁₂ …… Load resistance, D ₁₃ , D ₁₄ …… Leakage prevention diode. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A magnetic recording / reproducing circuit having a recording / reproducing head, a recording circuit and a reproducing circuit each having a pair of differential amplifying transistors, the collector of the amplifying transistor of the reproducing circuit being connected to a current supply path. A diode for preventing a leak current caused by a counter electromotive force generated by switching between conduction and non-conduction of the differential amplification transistor of the recording circuit is provided between the load resistor and the load resistor. A magnetic recording / reproducing circuit, the cathode of which is connected to the amplifying transistor side and the anode of which is connected to the load resistor side, and a reproduction output is taken out from a connection point of the load resistor and the diode.