JPS6025816B2 - magnetic playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic reproducing device that reproduces a recording signal recorded on a magnetic recording medium by frequency modulation.

Among these types of magnetic reproducing apparatuses, a VTR which records and reproduces video signals by frequency modulating them will be described below as an example.

In general, a VTR is configured such that an FM signal reproduced by a magnetic head is amplified by a preamplifier, and then FM demodulated to amplify the image and obtain a video output. Assume that the frequency band of an FM signal reproduced from a certain magnetic tape is band 1 (indicating the spectral distribution of the reproduced signal) as shown by the solid line in FIG. In addition,
In Figure I, the diagonal line downward to the left corresponds to the frequency shift of the carrier wave in the reproduced FM signal of band 1, and the solid lines on both sides correspond to the sidebands. . At this time, the frequency characteristics of the front layer multiplier, including the characteristics of the magnetic head, are determined by resonance between the inductance L of the magnetic head and the input capacitance C of the front layer multiplier, as shown in FIG. As shown in FIG. 2, the frequency characteristic 2 is set to be optimal for the reproduced FM signal in band 1, and the resonant frequency is fixed near the upper limit of the carrier wave frequency of the FM signal. However, a VT with such a configuration
When an FM signal recorded on another magnetic tape is reproduced using R, the other magnetic tape is of a different type from the magnetic tape on which the FM signal of Band 1 is recorded, and the reproduced FM signal is The frequency band of the signal is band 3 as shown by the broken line in FIG. 1 (indicating the spectral distribution of the reproduced signal).

), and the carrier wave frequency is lower than that of the FM signal of band 1 mentioned above.As shown in Fig. 1, for the FM signal of band 3 mentioned above, Since the frequency band of the device is too wide, there is a disadvantage that the S/N ratio of the reproduced signal deteriorates. In addition, in FIG. 1, the diagonal line downward to the right corresponds to the frequency shift of the carrier wave in the reproduced FM signal of band 3, and the dotted lines on both sides thereof correspond to the sidebands. On the other hand, if an FM signal in Band 1 is reproduced using a VTR equipped with a front-layer amplifier whose frequency characteristics are set to be optimal for an FM signal in Band 3, the carrier wave will be suppressed. Therefore, there is a problem that overmodulation development occurs. The present invention has been made in view of the above points, and the present invention has been made in such a manner that the pass frequency band of the direct multiplier to which the modulation signal from the magnetic head is combined is set to the magnetic recording medium provided in the cartridge housing the magnetic recording medium. The magnetic recording medium is detected by the medium type identification means, and the pass frequency band of the front layer intensifier is configured to be switchable in accordance with the detection output so as to match the frequency band of the corresponding magnetic recording medium. As a result, even if the superimposed modulation signal is reproduced from multiple types of magnetic recording media on which modulation signals with different carrier frequencies are recorded, the S/N ratio will not deteriorate or any overmodulation phenomenon will occur, and the result will always be good. The present invention provides a magnetic reproducing device capable of reproducing the above modulated signal under the following conditions.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing an example of an ephemeris intensifier which is a feature of the present invention.

In the figure, 4 is a magnetic head, 5 is a matching transformer, 6 is an adjustment trimmer capacitor, 7 is a varicap capacitor whose capacitance changes depending on the applied voltage, and resistor 8
A control voltage Ec is applied via. 9 is a first-stage amplifier transistor.

In such a configuration, assuming that the capacitance of the trimmer capacitor 6 is CT, the capacitance of the varicap capacitor 7 is Cv, and the stray capacitance of the circuit is Cs, the total capacitance C is expressed by the following equation (1).

C=CT+CV0CS...(1) Then, the frequency characteristic of the pre-counterfeit multiplier is the imaginary part of the inductance L seen from the multiplier side through the matching transformer 5 of the magnetic head 4, and the above-mentioned total capacitance C. Therefore, by changing the control voltage Ec applied to the varicap capacitor 7 according to the type of magnetic tape played by the magnetic head 4, the capacitance Cv of the varicap capacitor 7 can be adjusted. The resonance point of the preamplifier can be moved by changing the
In any case where modulated signals with different carrier frequencies are reproduced, the reproduced FM signal can be given an optimal frequency characteristic as in the case of band 1 and frequency characteristic 2 shown in FIG.

3 to 5 are circuit diagrams showing other examples of the front layer intensifier that is a feature of the present invention, and in each figure, the same reference numerals as in FIG. 2 indicate the same or corresponding parts, respectively. be.
In FIG. 3, a single fixed current capacitor 11 is a switching transistor, the base of which is connected via a resistor 8 to a voltage source of a control voltage Ec.

In such a configuration, when reproducing an FM signal of a certain carrier frequency, the control voltage Ec is not applied to the switching transistor 11, and the transistor 11 is turned off.
F and disconnect the fixed capacitor 10.

The total capacitance C in this case is expressed by the following equation (0).
C=CT10C3.・-(〇) Therefore, the frequency characteristic of the front layer intensifier in this case is that the inductance L seen from the intensifier side through the matching transformer 5 and the above-mentioned total capacitance resonates with the magnetic head 4. Therefore, by setting the capacitance CT of the trimmer capacitor 6 to a predetermined value in advance, it is possible to provide an optimum frequency characteristic for the FM signal of the above-mentioned certain carrier frequency.

On the other hand, when reproducing FM signals of different carrier frequencies, a control voltage Ec is applied to the switching transistor 11 to turn on the transistor 11 and a fixed capacitor 10 is added.

In this case, the total capacitance C is the capacitance of fixed capacitor 0.
When F, it is expressed by the following equation (m). C=C, 10CF
+Cs ... (m) Therefore, as mentioned above, the resonance point of the front layer multiplier can be moved, and by setting the capacitance CF of the fixed capacitor 10 to a predetermined value in advance, the above-mentioned different carrier wave frequencies can be adjusted. It is possible to provide optimum frequency characteristics for the FM signal.

Fig. 4 is an example of a modification of the circuit shown in Fig. 3.The difference from Fig. 3 is that a DC blocking capacitor 2 and a Dambiwag resistor are connected in parallel to a series circuit consisting of a fixed capacitor 10 and a switching transistor 11. 13 and a switching transistor 14 are connected in series, and a voltage source of a control voltage Ec is connected to the base of the switching transistor 4. According to such a configuration, the movement of the resonance point of the prefailure multiplier is controlled by the operation of the switching transistor 11, and
Similar to the case shown in the figure, but switching transistor 1
When 1 is N, the other switching transistors 14 are also N, and the damping resistor 13 is connected, so that the resonant frequency can be moved and the damping of the resonance can also be changed. Next, FIG. 5 differs from FIG. 3 in that a fixed capacitor 5 is additionally connected between the collector of the switching transistor 11 and the ground.

In such a configuration, when reproducing an FM signal of a certain carrier frequency, the control voltage Ec is not applied to the switching transistor 11, and the transistor 11 is connected to the RFF.
to form a series circuit of fixed capacitors 10 and 15. Then, the total capacitance C in this case is expressed by the following equation (W), where C is the capacitance of the added fixed capacitor 5. C = CT + CS + 1
By setting the respective capacitances CF and C,5 of 5 to predetermined values in advance, it is possible to provide the optimum frequency characteristics for the FM signal of the above-mentioned certain carrier frequency.

On the other hand, when reproducing an FM signal with a different carrier frequency, a control voltage Ec is applied to the switching transistor 11 to turn on the transistor 11 and disconnect the added fixed capacitor 15.

Then, since the total capacitance C in this case is expressed by the above-mentioned equation (m), the resonant capacitance changes compared to when the transistor 11 is turned off as described above. Therefore, since the resonance point of the preamplifier can be moved, by setting the capacitance CF of the fixed capacitor 10 to a predetermined value in consideration of the case where the transistor 11 is RFF,
Optimal frequency characteristics can also be provided to FM signals having different carrier frequencies. Note that in each example of the front layer multiplier described above, a method for controlling the control voltage Ec applied to the varicap capacitor 7 or a method for controlling the supply of the control voltage Ec to the switching transistor 11 is not specifically illustrated. However, since magnetic tapes are generally housed in cartridges, for example, if there are two carrier wave standards for recording and each standard has a different center frequency or maximum frequency deviation, or if the characteristics of the magnetic tape If different, the key groove of the cartridge for identifying the magnetic tape is used as a means for identifying the type of magnetic tape, and the presence or absence of a key groove that conforms to the above standard is detected by a known mechanical or optical method. By switching the control voltage, it is possible to turn on and off the power supply only by removing the cartridge.

Furthermore, an example has been described in which the resonance point of the multiplier is moved by changing the total capacitance C. It goes without saying that the above resonance point can be moved by changing the inductance L seen from the intermediate device side.

As described above, according to the present invention, the type of magnetic recording medium is detected by the magnetic recording medium type identification means, and the passing frequency band of the pre-calendar multiplier is determined based on the detected output. Since it is configured to be switchable to match the frequency band of the medium, even when reproducing the above modulated signal from multiple types of magnetic recording media on which modulated signals with different carrier wave frequencies are recorded, there is no need to perform the usual process of inserting a cartridge. By just using the software, it is possible to automatically provide the optimum frequency characteristics according to the carrier frequency of the modulated signal regenerated to the pre-layer multiplier, thereby preventing deterioration of the S/N ratio or overmodulation phenomenon. The modulated signal can always be reproduced in a good condition without causing problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the frequency band of the reproduced FM signal and the frequency characteristics of the front-layer amplifier, and FIG. 2 is a circuit diagram showing an example of the front-layer amplifier, which is a feature of the present invention. FIGS. 3 to 5 are circuit diagrams showing other examples of the front elongated middle device, each of which is a feature of the present invention. In the figure, 4 is a magnetic head, 5 is a matching transformer, 6 is a trimmer capacitor, 7 is a varicap capacitor, 9 is a boosting transistor, 10 is a fixed capacitor, 1
1 is a switching transistor, and 15 is a fixed capacitor. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a magnetic reproducing device that uses a magnetic head to reproduce the modulated signal from a plurality of types of magnetic recording media in which information is frequency-modulated and recorded in different frequency bands according to coercive force,
The type of the magnetic recording medium is detected by means for identifying the type of magnetic recording medium provided in the cartridge containing the magnetic recording medium, and the modulation signal from the magnetic head is combined in accordance with the detected output. A magnetic recording/reproducing device characterized in that the pass frequency band of an amplifier is switchable so as to match the frequency band of a corresponding magnetic recording medium.