JP2654388B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus suitable for improving the performance of a head amplifier using a magnetic head and obtaining certain reproduction equalization characteristics. Circuit.

[Conventional technology]

As described in Japanese Patent Publication No. 60-80104, a conventional device extracts a signal reproduced from a magnetic head with a rotary transformer, directly inputs the signal to a reproduction preamplifier, and a capacitor connected between the preamplifier input and the ground. The signal is amplified through a resonance circuit between the magnetic head and the magnetic head.

[Problems to be solved by the invention]

In the above prior art, the resonance circuit at the input end of the reproduction preamplifier increases the signal source impedance of the preamplifier by resonance, improves the NF of the amplifier, and equalizes the frequency characteristics of the FM signal to be reproduced. Since the impedance of the magnetic head used in the home VTR is too small for the noise matching of the reproduction preamplifier, the step-up of the signal source and the input resonance by the transformer are performed.

Conventionally, the wound type ferrite magnetic head used in a home VTR has a relatively high Q (Q ≒ 3), so the resonance can improve the NF of the preamplifier. Since the impedance of the head also fluctuates due to variations in the gap length, depth, and the like, a constant reproduction equalization characteristic cannot be obtained, and thus adjustment is required.

Recently, magnetic heads using thin film technology have begun to be adopted in VTRs. The thin-film head has a feature that the winding is also made by the thin-film technology, the head shape can be reduced, so that the reproduction efficiency is good, and the stray inductance is reduced, so that the inductance can be reduced. On the other hand, since the winding pattern cannot be made thick, there is a problem that the DC resistance is increased and Q is reduced (Q
≒ 1). For this reason, in the configuration of the conventional reproduction preamplifier,
Even if resonance is provided, the signal source impedance of the preamplifier cannot be increased, the NF is degraded, and the characteristics required for reproduction equalization cannot be obtained.

An object of the present invention is to provide a head amplifier that solves the above-mentioned conventional problems.

[Means for solving the problem]

The above object is achieved by connecting a coil in series between the magnetic head and the reproducing preamplifier, connecting a capacitor between the input of the preamplifier and the ground, and applying negative feedback from the output of the reproducing preamplifier to the input.

[Action]

The coil is selected to have a relatively large value with respect to the impedance of the impedance of the magnetic head viewed from the preamplifier side. Therefore, a high Q coil is connected in series to the magnetic head, and the Q of the magnetic head is equivalently increased.
Therefore, the resonance characteristic obtained by a magnetic head having a high Q equivalent to the capacitor on the input side of the preamplifier also has a high Q, and the signal source impedance of the preamplifier can be increased even in a low Q head as in the conventional case. Therefore, the NF of the amplifier can be improved without particularly adding a step-up transformer, and reproduction equalization by resonance is possible.

Further, since the coil has a relatively large value than the inductance of the magnetic head and uses individual components like a capacitor, the Q variation of resonance remains, but the resonance frequency is less affected by the inductance variation of the magnetic head. On the other hand, the Q variation of the head can make the resonance Q in the overall characteristics independent of the head Q by applying sufficient negative feedback from the output of the reproduction preamplifier to the input. Therefore, a non-adjustable preamplifier with little variation in frequency characteristics can be realized.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a block diagram of a circuit from a recording amplifier input to a reproduction preamplifier output of a magnetic recording / reproducing apparatus to which the present invention is applied. 1 is a recording medium, 2 is a magnetic head, 3 is 1: n
, 4 and 5 are recording / reproduction changeover switches, 6 is an impedance conversion circuit, 7 is a feedback damping circuit, 8 is a reproduction amplifier, 9 is a recording amplifier, 10 is a reproduction amplifier output terminal, and 11 is a recording amplifier input terminal.

At the time of recording, the magnetic reproduction changeover switch 4 is grounded, and 5 is connected to a recording amplifier. The recording signal is amplified by the recording amplifier 9, battery-amplified n times by the transformer 3, and recorded on the recording medium 1 via the magnetic head 2.

At the time of reproduction, the recording / reproduction switch 4 is connected to the impedance conversion circuit 6, and 5 is grounded. The signal output from the recording medium 1 to the magnetic head 2 is
The voltage is amplified twice, passes through the impedance conversion circuit 6, enters the reproduction amplifier 8, is amplified, is subjected to negative feedback by the feedback damping circuit, and is output to the reproduction amplifier output terminal 10.

FIG. 3 is an equivalent circuit when the primary side of the transformer 3 is converted to the secondary side during the recording shown in the block diagram of FIG. When the recording / reproduction changeover switch 3 is grounded, the load seen from the recording amplifier becomes only the head, which is the same as the conventional one.

FIG. 5 is a specific circuit example at the time of reproduction shown in the block diagram of FIG. 16, 17 are inductance L _s and capacitance C _s of the impedance conversion circuit, 18 is a coupling capacitor, 25 is a damping resistor R _D , and Q ₁ and Q ₂ in the reproduction amplifier 8 are cascode amplifiers whose outputs are passed through an emitter follower. The playback output terminal 10 is used.

The operation of FIG. 5 will be described with reference to FIG. 2 showing an equivalent circuit of FIG. FIG. 2 is an equivalent circuit when the primary side of the transformer 3 is converted to a secondary side. 12 is the head output signal
e _M , 13 is the head output noise e _n , 14, 15 is the head resistance n
² R _H, the inductance n ² L _H, 30 are those of the resistance R _P is provided between ground and the reproducing amplifier input terminal so as to be equivalent to the feedback damping resistor 25.

The gain of the reproducing amplifier A, comes to the feedback damping resistor and R _F of the equivalent resistance R _P as follows expressed in the R _F.

Further, using each element n ² R _H , n ² L _H , L _S , C _S , R _P of the equivalent circuit, the input / output characteristic up to the input terminal of the reproduction amplifier of the equivalent circuit is expressed by the following equation. Can be represented by

Ω is an arbitrary angular frequency, and j is It is.

The input of the equivalent circuit is V _i , and the output at the input terminal of the reproducing amplifier is
If V _o L ′ _H = n ² L _H + L _S and the above equation (2) is further transformed, When the resonance angular frequency of the equivalent circuit and ω _o, Substituting equation (4) into equation (3) gives here, Substituting equations (7) and (8) into equation (5), The general formula of the transfer function of the equivalent circuit is as follows, where K is a coefficient, ω _o is a resonance angular frequency, and Q is a circuit Q.

Therefore, the equations (9) and (10) are compared to determine the Q of the equivalent circuit. Becomes Here, the resonance angular frequency ω _o of the equivalent circuit is given by equation (4). It is.

If a value that satisfies the condition of damping resistance R _P >> n ² R _H is selected, Becomes L' _{H in} equation (12) is the inductance of the head.
n ² L _H and inductance L _S in the impedance conversion circuit
Therefore, if the inductance L _S is relatively larger than the inductance n ² L _H , variation in resonance frequency due to variation in head inductance can be reduced. Further, the inductance L _S and the resonance capacitor C _S
Since the value can be managed, a constant resonance frequency with little variation can be obtained without adjustment using a variable capacitor or the like.

The Q of the equivalent circuit is given by the following equation (11). Assuming that Q at the resonance point of the equivalent circuit is Q _o , the above R _P >> n ²
If the condition of R _H is satisfied Becomes

Wherein the above formula (6), from (7), Q ₁ is Q when no damping resistance R _P in the equivalent circuit, the head of the Q
Is low, Q can be increased by the inductance L _S of the impedance conversion circuit. Conventionally, a diping resistor is provided in order to reduce the variation in Q of the circuit due to the variation in impedance of the head. However, when the Q of the head is low, the signal source impedance of the reproducing amplifier cannot be increased due to the damping effect. NF could not be improved, and reproduction equalization characteristics could not be obtained. According to the present invention, even if the Q of the head is low, and the Q of the head varies due to the variation of the inductance of the head, the inductance L _S in the impedance conversion circuit is made smaller than the inductance n ² L _{H of the} head. Since the size is increased, the Q of the head viewed from the reproduction amplifier side can be increased, and the variation in Q due to the variation in inductance of the head can be reduced. Equation (13) is a Q of the equivalent circuit, the feedback damping resistor R _F, and it can reduce the Q variation due to the variation in resistance n ² R _H of the head,
Since Q ₁ in the equation (13) can be increased by the inductance L _S in the impedance conversion circuit, the Q of the equivalent circuit can be increased.
Indicates that even if damping is performed, Q can be set to an appropriate size by selecting an appropriate value for Q ₁ and R _P in the equation (13).

For example, change the head resistance R _H to 20Ω inductance and 0.6
If μH, step-up transformer is 1: 2 (= n), inductance L _S in the impedance conversion circuit is 10 μH, capacitance C _S = 50PF, and damping resistance R _P = 1.5KΩ, the resonance frequency is 6.4MHz, and the Q of the circuit Becomes 2.0. In addition, the Q of the head is 1.1, and about twice the Q can be obtained even if damping is performed. Also, in the above example, if the head resistance varied by 10% and became 22Ω, Q would be 1.97. Compared with Q = 2.0 when there was no variation, there was almost no change, and the Q of the circuit due to the variation in the head resistance was small. There is almost no variation.

Therefore, even if the Q of the head is low, the signal source impedance of the reproduction amplifier can be increased by the impedance conversion circuit and the feedback damping circuit, so that the NF of the reproduction amplifier can be improved, and the impedance variation of the head can be improved. Q variation and resonance frequency variation of the circuit can be reduced.

If the inductance L _S in the impedance conversion circuit is increased in order to increase the Q of the circuit, the capacitance C _S in the impedance conversion circuit must be reduced in order to keep the resonance frequency constant. When the input capacitance of the amplifier is large, even if the capacitance C _S in the impedance conversion circuit is reduced, the Q of the circuit cannot be increased at a constant frequency because the input capacitance of the reproduction amplifier is large. It is better to use a FET with a small input capacitance as a cascode type amplifier in the first stage.

Figure 4 is a reproduction of when the resonant frequency when the f _o, the case of using an impedance conversion circuit and the feedback damping circuit of the present invention, and in the case of performing the resonance only Q of the head, is not performed resonance It shows the frequency characteristics of the head output signal, the frequency characteristics of the resistance (real part of impedance) of the head, and the frequency characteristics of the noise of the reproduction amplifier at the amplifier input terminal. I is the frequency characteristic of the head output signal when the impedance conversion circuit and the feedback damping circuit of the present invention are used, and II is the head Q
Frequency characteristics of the head output signal when resonating only,
III is the frequency characteristic of the head output signal when no resonance occurs, and I 'is the frequency characteristic of the head resistance when the impedance conversion circuit and the feedback damping circuit are used.
II 'represents the frequency characteristic of the resistance of the head when resonated only by the Q of the head, III' represents the frequency characteristic of the resistance of the head when not resonated, and IV represents the frequency characteristic of the noise of the reproducing amplifier. Conventionally, when a head having a low Q is used, the signal source impedance of the reproducing amplifier cannot be increased even when the head is resonated, and the signal source impedance of the reproducing amplifier also varies due to the variation in the impedance of the head. Degraded the NF and did not obtain the characteristics required for constant reproduction equalization (FIG. 4 II). Even when a head having a higher Q is used, both the resonance frequency and the Q vary due to variations in the impedance of the head, so that a constant reproduction equalization characteristic cannot be obtained. Conventionally, it was possible to adjust the resonance frequency of a head having a high Q by using a variable capacitor as a resonance capacitor. Also, in the head with high Q,
Although the variation in Q could be reduced by performing feedback damping, the resonance frequency had to be adjusted by adjusting the capacitance of the resonance capacitor, and the characteristics necessary for reproduction equalization could not be obtained due to feedback damping. A new circuit had to be provided to degrade the NF of the amplifier and obtain the characteristics required for reproduction equalization. With the impedance conversion circuit and the fee zone back damping circuit of the present invention, the head signal as shown in FIG. 4 I, I 'is Q times at the resonant point, the resistance of the head can ^double Q. By increasing the inductance in the impedance conversion circuit from the inductance of the head, the resonance frequency and Q variation due to the variation in the inductance of the head can be reduced, so that it is not necessary to adjust the capacitance of the resonance capacitor in particular to adjust the resonance frequency. , A constant resonance frequency can be obtained. From the reproduction amplifier side, the Q of the head is equivalently increased by the inductance in the impedance conversion circuit,
Q variation is also reduced. Further, by performing feedback damping on Q enhanced by the impedance conversion circuit, variation in Q due to variation in resistance of the head can be reduced. Therefore, even in a head having a low Q, the Q of the head viewed from the reproduction amplifier side is equivalently increased by the impedance conversion circuit, and the signal source impedance of the reproduction amplifier is increased by the impedance conversion circuit and the feedback damping circuit (FIG. 4). I ′) makes it possible to improve the NF of the reproduction amplifier and to obtain a constant reproduction equalization characteristic without variation (II ′ in FIG. 4) without adjustment.

FIG. 6 shows that the inductance of the impedance conversion circuit is provided on the primary side of the transformer during reproduction.
The effect is the same as when it is attached to the secondary side, but since it passes through the transformer, it becomes n ² times from the reproduction amplifier side, so compared to when the inductance is on the secondary side of the transformer
1 / n ² is good.

FIG. 7 is an example of a reproduction circuit when there is no transformer. The NF in the low band cannot be improved compared to the case with the transformer because the signal source impedance of the reproduction amplifier is low because there is no transformer, but the NF can be improved by resonance in the high band.
Therefore, regardless of the presence or absence of a transformer, the Q and resonance frequencies are determined by the impedance conversion circuit and the feedback damping circuit, so that the degree of freedom in selecting the Q and resonance frequencies is large.

Improving NF by increasing the signal source impedance can be realized even if the turns ratio of the transformer is increased,
In a rotary transformer that requires multiple channels in a small-diameter cylinder, such as a VTR, the number of turns cannot be large. Therefore, it is necessary to provide a step-up transformer before the reproduction preamplifier. However, the present invention does not require this transformer and can realize impedance conversion with a simple circuit. The seventh
As shown in the figure, even in a system that does not require a rotary transformer, a large Q can be obtained in the present invention, so that a step-up transformer can be eliminated.

FIG. 8 is a specific example of the block diagram of FIG. 19,2
0 is a recording / playback switching control terminal. At the time of recording, the recording / reproduction changeover switches 4 and 5 are switched by setting the recording / reproduction changeover control terminal 19 to high and 20 to low.
Is turned on, and the terminal of the transformer 3 connected to the switch 4 is grounded so that the impedance conversion circuit or the like of the reproducing system does not become a load. The switch 5 is turned off and the recording current output from the recording amplifier 9 is turned off. But transformer 3
Through the head to the head.

At the time of reproduction, the switch 5 is turned on by setting the recording / reproduction switching control terminal 19 to low and 20 to high, and the terminal of the transformer 3 connected to the switch 5 is grounded, so that the recording amplifier and the like of the recording system are connected. So as not to be a load,
Further, the switch 4 is turned off, and a signal output from the head is supplied to the impedance conversion circuit 6, the feedback damping circuit 7, and the reproduction amplifier 8 via the transformer 3. The switch 4 is located between the inductance and the capacitance of the impedance conversion circuit 6 as in the conventional case. However, in this case, when recording, the inductance and the feedback damping circuit act as loads. As shown in FIG. 8, the inductance of the impedance conversion circuit 6 must be provided between the transformers 3. In the case of reproduction only, the coil 16 and the damping resistor 25 may be connected between the magnetic head 2 and the transformer 3 as shown in FIG. 6, but in a recording system, the recording coil 16 and the damping resistor 25 are connected. The resistance 25 acts as a load, requiring a large dynamic range for the recording amplifier. Therefore, when recording / reproducing is performed via a rotary transformer using a magnetic head for recording / reproduction as in a home TR, as shown in FIG. 1, recording is performed so that the impedance conversion circuit 6 does not become a load during recording. A reproduction switch 4 needs to be provided.

〔The invention's effect〕

According to the present invention, even with respect to a head having a low Q and a variation in the impedance of the head, an impedance conversion circuit for equivalently increasing the Q of the head and a feedback that eliminates the variation in the resistance (real part) of the impedance of the head are provided. Input to the preamplifier via the damping circuit improves the NF of the regenerative amplifier, and the impedance conversion circuit and feedback damping circuit can obtain a constant re-equalization characteristic with little influence of head impedance variation without adjustment. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is an equivalent circuit diagram at the time of reproduction, FIG. 3 is an equalization circuit diagram at the time of recording, and FIG. , The frequency characteristic of the resistance (real part) of the head and the frequency characteristic of the noise of the reproducing amplifier, FIG. 5 is a circuit diagram showing a specific circuit example at the time of reproduction, and FIG. FIG. 7 is a circuit diagram showing an example of a circuit when the inductance and the damping resistance of the impedance conversion circuit are placed on the primary side of the transformer.
FIG. 8 is a circuit diagram showing a circuit example when the transformer is deleted during reproduction, and FIG. 8 is a circuit diagram showing a specific example of the block diagram shown in FIG. 1. Recording medium 2, Magnetic head 3 Transformer (1: n) 4, 5 Recording / reproduction switch 6 Impedance conversion circuit 7 Feedback damping circuit 8 Reproduction amplifier 9, ... Recording amplifier 16 ... Inductance of impedance conversion circuit 17 ... Capacitance of impedance conversion circuit 25 ... Damping resistance.

Claims (2)

(57) [Claims] 1. A magnetic recording / reproducing apparatus having at least a magnetic head and a preamplifier for amplifying a signal reproduced by the magnetic head, comprising: a coil connected in series between the magnetic head and an input of the preamplifier; An impedance conversion circuit comprising a capacitor connected between the input of the preamplifier and the ground to obtain a Q larger than the Q of the magnetic head itself; and a damping Q provided in parallel with the preamplifier and enhanced by the impedance conversion circuit And a feedback damping circuit for obtaining a constant reproduction equalization characteristic. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the first-stage element of the preamplifier is constituted by an FET.