JP2577728B2 - Magnetic recording / reproducing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing circuit, and more particularly to an improvement in input conversion noise of a reproducing circuit in a magnetic recording / reproducing circuit such as a floppy disk drive, and a reduction in power supply voltage. It also relates to improvement of voltage characteristics.

[Conventional technology]

FIG. 2 shows a conventional magnetic recording reproduction circuit for a floppy disk having two sets of magnetic heads. In the figure, WG is a signal indicating a recording state or a reproduction state, SIDE is a signal for selecting a magnetic head, Ha and Hb are each a magnetic head, 1 is a control circuit for a center tap circuit, and the WG signal and the SIDE signal are Receiving transistors Q _1a , Q _1b , Q _2a , Q
_2b and the resistor _{R 1a, R 1b, R 2a} , together with R _2b, and selects setter tap terminal 1a, a 1b. Further, WR DATA is a recording signal, 2 is a control circuit for a recording circuit, and Q ₃ and Q ₄ are transistors constituting a recording differential pair, which are turned on and off by the control circuit 2 repeatedly. 3 constant current source recording circuit, Q ₅ is a transistor for determining the current flowing in the transistor Q _3, Q ₄ together with R _3.

D _{1a to} D _10a and D _{1b to} D _10b are diodes constituting a diode matrix switch circuit, and are voltage values under the respective conditions of the center tap terminals 1a and 1b, that is, the voltages of the recording / reproducing, the selected head and the non-selected head. It is controlled by the voltage value of each condition, and performs circuit control in each state. Each of these diodes on the semiconductor integrated circuit is generally _{D 1a ~D 8a (D 1b ~D} 8b) is NP
N transistor collector / base direct connection type,
D _9a and D _10a (D _9b and D _10b ) are the collectors of PNP transistors.
It is formed with a base direct connection type. Reverse breakdown voltage of each diode is about 7V for NPN structure and about 30V for PNP structure
That is all.

Reference numeral 4 denotes a constant current source for a reproduction circuit, Q ₆ and Q ₇ are transistors controlled by the current source, R ₄ and R ₅ are resistors, D ₁₁ and D ₁₂ are diodes for preventing a leakage current described later, and R ₇ to R ₁₂ is resistance, Q
₉ and Q ₁₀ are transistors constituting a differential amplifier for reproduction, Q ₈
Together with resistors R ₆ is a transistor for determining the current flowing in the differential amplifier.

 Next, the operation will be described.

First, regarding the head selection and switching between recording and reproduction, the control circuit 1 for the center tap circuit which receives the SIDE signal and the WG signal controls each of the transistors _1a , _Q1b ,
Controls the on / off of Q _2a and Q _2b , and controls the center tap terminals 1a,
This is performed by controlling the voltage value of 1b. Optionally during playback (saturation voltage of Q _2a) makes it inoperative transistor Q _1a, applied to (resistor R _1a - for example, when the head Ha is selected, the voltage of the terminal 1a is the time of recording, (supply voltage V _cc) Voltage) − (V _{BE of} Q _2a ). (V _BE is the base-emitter voltage). At this time, the voltage of the terminal 1b on the non-selection side becomes 0V.

 When the head Hb is selected, the operation is reversed.

Next, at the time of recording, the control circuit 2 for the recording circuit and the constant current source 3 for the recording circuit are operated by the WG signal,
As a result, the transistors Q ₃ and Q ₄ forming the differential pair repeat the on / off operation with each other according to the WR DATA signal. The current flowing at this time depends on the transistor Q ₅ ,
A constant current determined by the resistor R _3. At the time of this recording, the reproduction circuit constant current source 4 is deactivated, and the transistors Q ₆ , Q ₇ , Q ₈ connected thereto are deactivated.

Next, at the time of reproduction, the operation is reverse to that at the time of recording. The constant current source 4 for the reproduction circuit is operated by the WG signal, and the constant current source 3 for the recording circuit is turned off. A reproducing circuit for reading recorded data in this case will be described below.

The subtle playback output signal from the head is a diode D _9a
(D _9b ), D _10a (D _10b ) and D ₁₁ and D ₁₂ are input to a differential amplifier composed of transistors Q ₉ and Q ₁₀ , where they are amplified. The bias of the circuit is applied to transistors Q ₆ and Q ₇
Constant current source is determined voltage reproduction of the center tap terminal 1a (1b), and a resistor R _7, R _8.

[Problems to be solved by the invention]

In the circuit configured as described above, when the transistor Q ₃ or Q ₄ changes from conduction to non-conduction by the WR DATA signal during recording, L 3
· (Di / dt) (where, i is the current value flowing through the transistor Q ₅₎ counter electromotive force is generated in the magnetic head terminal. The value of this back electromotive force becomes a problem particularly in the case of a device for a floppy disk (the value of L is large in the case of a floppy disk), and varies depending on the values of L and i to reach a value several times _Vcc. There are cases. Then, when such a back electromotive force is generated at the magnetic head terminal, this causes the voltage to _Vcc through the resistor R ₇ (R ₈ ) and the base → collector → resistance R ₁₁ (R ₁₂ ) of the transistor Q ₉ (Q ₁₀ ). ), A leak current flows to _Vcc . So to prevent this, diode D
₁₁ is the D ₁₂ is provided. This diode D ₁₁ ,
D ₁₂ is usually a PNP structure described above.

As described below, in the conventional magnetic recording / reproducing circuit, diodes D ₁₁ and D ₁₂ are required to prevent a leak current, and the diodes D ₁₁ and D ₁₂ are provided. As a result, the base resistances of the transistors Q ₉ and Q ₁₀ increase. For this reason, the input conversion noise of the differential amplifier of the reproduction circuit increases, and the performance of recording and reproduction deteriorates. For example, there is a problem that a weak signal cannot be reproduced.

The present invention has been made in view of such a point, and can improve input conversion noise of a differential amplifier in a reproduction circuit section,
It is another object of the present invention to provide a magnetic recording / reproducing circuit capable of improving the voltage reduction characteristics of a power supply voltage.

Here, the conventional circuit will be considered in more detail.
Now, when a differential amplifier as shown in FIG. 3 is considered, generally, the equivalent input noise eni of the differential amplifier is eni = 2 × [2q Ie Δf ｛Re + (rb ′ + RG) / β｝ ² + 2kt (RE + rb ′) Δf] ^1/2 . rb 'is the base spreading resistance of the amplification stage NPN transistor, and rb' of the NPN transistor is usually about several ohms. Δf is the signal bandwidth, Re is the emitter resistance of the transistor Tr itself, and β is the current amplification.

The aforementioned rb 'is, in the conventional of reproducing circuit shown in Figure 2 corresponds to equivalently (operating resistance of the D _9a) + (operating resistance of the D ₁₁₎ + (base spreading resistance of Q _9). Operation resistance in passing a 100 .mu.A current to the diode D _9a and D ₁₁ are respectively become (q / kT) / 100μA ≒ 260Ω. Also, the base spreading resistance of an NPN transistor is usually about several Ω.

From the above, reducing the rb 'in the formula of the eni can reduce the equivalent input noise, therefore, if deleting a diode D ₁₁ in the prior art while preventing the leakage current due to reverse electromotive force by some means It is considered that the input conversion noise level of the reproducing circuit can be reduced.

[Means for solving the problem]

In the magnetic recording / reproducing circuit according to the present invention, the same number of pairs of transistor for differential amplification of the recording circuit and the reproducing circuit as the recording / reproducing head are provided, thereby selecting the recording / reproducing head. In addition to the direct connection, the differential amplifier transistor pair of the recording circuit is directly connected to each of the recording / reproducing heads, and further, instead of the diode connected to each base of the differential amplifier transistor of the conventional reproducing circuit. A diode for preventing a leakage current is provided between each collector of the differential amplification transistor and the load resistance of the power supply circuit.

[Action]

In the present invention, since the diode for preventing leakage current is provided between the collector of the differential amplification transistor of the reproducing circuit and the load resistance of the current supply path, the number of diodes connected to the base of the transistor is reduced. In addition, the equivalent input resistance can be reduced to reduce the input conversion noise of the reproducing circuit. In addition, since the recording / reproducing head is directly connected to the power supply, the dynamic range of the voltage amplitude generated by the back electromotive force of the head can be increased to improve the voltage reduction characteristics of the power supply voltage. Since the transistor pair is directly connected to each of the recording / reproducing heads, the dynamic range of the voltage amplitude generated by the back electromotive force of the head at the time of recording can be increased, and the voltage reduction characteristics of the power supply voltage can be further improved.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a magnetic recording / reproducing circuit according to an embodiment of the present invention. In FIG. 1, the same reference numerals as those in FIG. Q _3a , Q _4a and Q _3b , Q _4b are transistors constituting a recording differential pair, and the differential pairs are respectively magnetic heads Ha, Hb
Is directly connected to the control circuit 2 for the recording circuit.
The ON / OFF operation is repeated by this. Q _9a , Q
_10a and Q _9b, Q _10b is a transistor that constitutes the reproduced differential amplifier, transistors A Q _6a for bias each base is controlled by the reproducing circuit constant-current source 4, respectively, Q
_7a , Q _6b , Q _7b connected, the emitter is also a transistor
They are connected to Q _8a and Q _8b and amplify each reproduction output signal of the magnetic heads Ha and Hb. D _13a , D _14a , D _13b , D _14b is P
This is a diode with an NP structure for preventing leakage current.
The cathode is connected to the collector of each transistor of the reproducing differential amplifier, and the anode is connected to resistors R ₁₁ and R ₁₂ connected to the current supply path. A reproduction output signal is output from a connection point between the anode and the resistors R ₁₁ and R ₁₂ .

 Next, the operation will be described.

At the time of recording, the magnetic heads Ha and Hb are selected by a recording differential pair including transistors Q _3a and Q _4a and Q _3b and Q _4b . That is, to the transistor Q _3b, the base potential of the Q _4b lower than the base potential of the transistor Q _3a, Q _4a when selecting the magnetic heads Ha, inputs a recording signal to the base of the transistor Q _3a, Q _4a. As a result, the recording signal is output to the magnetic head Ha, not to the magnetic head Hb, and the magnetic head Ha is selected. When selecting the magnetic head Hb, the above procedure is reversed.

Next, at the time of reproduction, selection of the magnetic heads Ha and Hb is performed by operating and not operating the differential amplifier for reproduction. That is, when selecting the magnetic head Ha, the transistors Q _6a , Q _7a , Q _8a
Is turned on, the transistors Q _6b , Q _7b , and Q _8b are turned off, and the reproducing differential amplifier including the transistors Q _9a and Q _10a is operated, and the reproducing differential amplifier including the transistors Q _9b and Q _10b is operated. Deactivate the amplifier. Magnetic head Hb
When selecting, the reverse of the above is performed.

In this manner, the selection of the magnetic head at the time of recording and reproduction is performed, and recording and reproduction are performed similarly to the conventional circuit.

In the circuit of this embodiment, the selection of the magnetic head is performed as described above, and the center tap voltage supply system and the diode matrix switch circuit provided in the conventional circuit are eliminated. That is, the magnetic head
Since Ha and Hb are directly connected to the power supply, the dynamic range of the voltage amplitude generated by the back electromotive force of the magnetic head can be increased by about 1 V, and since the recording differential pair is directly connected to the magnetic head, The dynamic range of the voltage amplitude generated by the back electromotive force of the magnetic head at the time of recording can be increased by 4V _BE , and the voltage reduction characteristic of the power supply voltage can be improved by the dynamic range that can be increased.

Further, in this embodiment circuit, since there is provided between the leakage resistance R ₁₁ of the current collector and the current supply path of the transistor of the diode for preventing regeneration differential amplifier, R _12, transistor reproduction differential amplifier Q _9a, Q _10a, Q _9b, reducing the number of diodes connected in series to the bases of Q _10b, the equivalent input resistance is small can be reduced equivalent input noise of the reproducing circuit. At the time of recording, the transistors Q _6a and Q _{6a
Since 7a} , _Q8a , _Q6b , _Q7b , and _Q8b are not operating, no leak current occurs from this path, and there is no problem.

Further, in the circuit of the present embodiment, the recording and reproducing circuits can be supplied from the same power supply, so that the external terminal pins, elements and the like can be simplified in the circuit configuration.

In the above embodiment, the case of two magnetic heads has been described.
The present invention can also be applied to a case where a pair of magnetic heads are provided, and has the same effect as the above embodiment.

〔The invention's effect〕

As described above, according to the magnetic recording / reproducing circuit of the present invention,
A diode for preventing leakage current is provided between the collector of the differential amplifier transistor of the reproducing circuit and the load resistance of the current supply path, and the recording / reproducing head is directly connected to the power supply, and the differential amplifier transistor pair of the recording circuit is connected. Are directly connected to each of the recording / reproducing heads, so that the input conversion noise of the reproducing circuit can be reduced and the voltage reduction characteristics of the power supply voltage can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a magnetic recording / reproducing circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a conventional magnetic recording / reproducing circuit, and FIG. 3 explains equivalent input noise of a differential amplifier. FIG. In FIG, Ha, Hb ...... magnetic _{head, Q 3a, Q 3b, Q} 4a, Q 4b ...
… Differential amplification transistor for recording circuit, Q _9a , Q _9b ,
Q _10a , Q _10b …… Differential amplification transistor for reproduction circuit, D
_13a , D _13b , D _14a , D _14b …… Diode for preventing leakage current,
Q _6a , Q _6b , Q _7a , Q _7b , Q _8a , Q _8b … Bias transistor, R ₁₁ , R ₁₂ … Load resistance. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A magnetic recording / reproducing circuit, comprising: a recording / reproducing head directly connected to a power supply; a recording circuit having a pair of differential amplifying transistors directly connected to each of the recording / reproducing heads; Amplifying transistor pair that is connected to the collector of the transistor for differential amplification and differentially amplifies the output of each of the read / write heads, the cathode is connected to the collector of the transistor for differential amplification, and the anode is connected to the load resistance of the current supply path. A reproducing circuit having a diode connected thereto, wherein a reproducing signal is output from an anode of the diode.