JPS6151324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic reproducing apparatus for reproducing a recorded signal recorded on a magnetic recording medium in frequency tones.

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

Generally, in a VTR, after the FM signal reproduced by the magnetic head is amplified by a preamplifier,
It is usually configured to perform FM demodulation and amplify the video to obtain video output. Assuming that the frequency band of the FM signal reproduced from a certain magnetic tape is Band 1 as shown by the solid line in Figure 1, the frequency characteristics of the preamplifier, including the characteristics of the magnetic head, are as follows. By creating resonance between the inductance L of the magnetic head and the input capacitance C of the amplifier, as shown in FIG.
The resonant frequency is fixed near the upper limit of the carrier wave frequency of the FM signal.

However, when a VTR with such a configuration is used to play back FM signals recorded on other magnetic heads, the other magnetic tape may be of a different type from the magnetic tape on which the band 1 FM signal was recorded. , the frequency band of the reproduced FM signal is band 3, as shown by the broken line in Figure 1, and is different from band 1 mentioned above.
If the FM signal has a lower carrier frequency than the FM signal, as shown in Figure 1, the frequency band of the preamplifier is too wide for the FM signal in band 3, so the reproduction is difficult. There is a disadvantage that the S/N ratio of the signal deteriorates. On the other hand, by using a VTR equipped with a pre-de-width filter whose frequency characteristics are set to be optimal for FM signals in band 3,
When reproducing an FM signal, the carrier wave is suppressed, resulting in an overmodulation phenomenon.

The present invention has been made in view of the above points, and includes an electrically connected trimmer capacitor for adjustment in a magnetic reproducing device in which a magnetic head reproduces a modulated signal from a magnetic recording medium in which information is recorded by frequency modulation. A fixed capacitor having a capacitance of a predetermined value changes the resonance point when connected, and a control signal corresponding to at least one of the maximum frequency deviation or center frequency of the signal recorded on the magnetic recording medium is input, and this control By providing a switching element that electrically connects or electrically disconnects the fixed capacitor to the adjustment trimmer capacitor based on a signal, there is less variation in the resonance point and less temperature dependence, making it possible to miniaturize the circuit configuration. Even if the modulation signal is reproduced from multiple types of magnetic recording media on which modulation signals of different frequencies are recorded,
The present invention proposes a magnetic reproducing device that can always reproduce the modulated signal in a good condition without deteriorating the S/N ratio or exhibiting an overmodulation phenomenon.

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

FIG. 2 is a circuit diagram showing an example of a preamplifier which is a feature of the present invention. In the figure, 4 is a magnetic head, 5 is a matching transformer to which this magnetic head is connected to the primary coil 5a, 6 is an adjustment trimmer capacitor connected in parallel to the secondary coil 5b of this matching transformer, and 7 is a matching transformer. The first stage amplifying transistor 8 has its base connected to the connection point A between the secondary coil 5b of the matching transformer 5 and the adjustment trimmer capacitor, and 8 is a transistor of a predetermined value whose one electrode is connected to the connection point A. A fixed capacitor consisting of a capacitor, 9 is a switching element consisting of a transistor connected between this fixed capacitor and ground, and a control voltage is connected to the base via a resistor 10.
Ec, that is, a control signal corresponding to at least one of the maximum frequency deviation or center frequency of the signal recorded on the magnetic recording medium is input, and in this embodiment, the cartridge identifying the magnetic recording medium is input. A control signal obtained using a keyway is input.

In such a configuration, at a certain carrier frequency,
When reproducing an FM signal, when the control signal obtained by detecting the key groove of the cartridge containing the magnetic recording medium is not the control voltage Ec, the switching element 9 is not applied with the control voltage Ec. 9 is in the OFF state. As a result, fixed capacitor 8 is electrically disconnected from adjustment trimmer capacitor 6. The total capacitance C in this case is expressed by the following equation ().

C=CT+CS...(1) However, CT is the capacitance of the adjustment trimmer capacitor 6, and CS is the stray capacitance of the circuit.

Therefore, the frequency characteristics of the preamplifier in this case are determined by resonance between the inductance L seen from the amplifier side through the magnetic head 4 through the matching transformer 5, and the above-mentioned total capacitance C. Therefore, by setting the capacitance CT of the adjustment trimmer capacitor 6 to a predetermined value, it is possible to provide the optimum frequency characteristics for the FM signal of a certain carrier frequency.

On the other hand, when reproducing FM signals with different carrier wave frequencies, the key grooves that house the magnetic recording media on which these different carrier waves are recorded are also different, and the control signal obtained by detecting this key groove becomes the control voltage Ec. Therefore, the control voltage Ec is applied to the switching element 9, and the switching element 9 is turned on.
As a result, the fixing capacitor 8 is electrically connected to the adjusting trimmer capacitor 6. The total capacitance C in this case is expressed by the following equation (2), where CF is the capacitance of the fixed capacitor 10.

C=Cr+CF+Cs...() Therefore, since the resonance point of the preamplifier can be moved as described above, by setting the capacitance CF of the fixed capacitor 10 to a predetermined value in advance, Optimal frequency characteristics can be provided to the FM signals having different carrier frequencies.

Moreover, since the capacitance value of the fixed capacitor 8 is constant and does not change due to temperature, the total capacitance C is also constant and there is no variation in the resonance point.
Moreover, since the switching element 9 determines whether or not the fixed capacitor 8 is completely electrically connected to the adjustment trimmer capacitor 6 based on the control signal, each resonance point can be set reliably. moreover,
Since the preamplifier only requires the addition of a fixed capacitor 9 and a switching element 10, it can be constructed without increasing its size.

FIG. 8 shows another example of the preamplifier which is a feature of the present invention, and is an example in which the circuit shown in FIG. 2 described above is modified. A series circuit consisting of a DC blocking capacitor 11, a damping resistor 12, and a switching transistor 13 is connected in parallel to the series circuit consisting of the element 9, and a control voltage Ec is applied to the base of the switching transistor 13. It is.

According to such a configuration, the movement of the resonance point as a preamplifier is controlled by the operation of the switching element 9, similar to that shown in FIG. 2 above, and when the switching element 9 is turned on, other The switching transistor 13 is also turned on, and the damping resistor 13 is connected, so that the damping of the resonance can be changed along with the movement of the resonance frequency.

FIG. 5 shows still another example of the preamplifier which is a feature of the present invention, in which the fixed capacitor 8
is connected to one electrode of the adjustment trimmer capacitor 6 via a capacitor 14, and the switching element 9 is connected in parallel to the fixed capacitor 8.

In such a configuration, when a certain carrier frequency
When reproducing an FM signal, the control voltage Ec is not applied to the switching element 9 as in the case shown in FIG.
It is in the OFF state, forming a series circuit of fixed capacitor 8 and capacitor 14. If the total capacitance C in this case is the capacitance C ₁₄ of the capacitor 14, then
It is expressed by the following formula ().

C=CT+CS+CF×C ₁₄ /CF+C ₁₄ Therefore, the preamplifier in this case has the capacitances CF and CF of the fixed capacitor 8 and the capacitor 14, respectively.
By setting C ₁₄ to a predetermined value in advance, it is possible to provide an optimal frequency characteristic for the FM signal of a certain carrier frequency.

On the other hand, when reproducing FM signals with different carrier frequencies, the control voltage Ec is applied to the switching element 9 in the same way as shown in FIG. Separate. The total capacitance C in this case is expressed by the following equation ().

C=CT+C ₁₄ +CS...() As described above, the resonance capacitance changes compared to when the switching element 9 is in the OFF state. Therefore, since the resonance point of the preamplifier can be moved, the capacitance _C14 of the capacitor 14 can be changed by the switching element 9.
By setting it to a predetermined value in advance, taking into consideration the case of the OFF state, it is possible to provide the optimum frequency characteristics even to the FM signals of different carrier frequencies.

In each example of the preamplifier described above, the method of controlling the supply of the control voltage Ec to the switching element 9 is not specifically illustrated, but since the magnetic tape is generally stored in a cartridge, 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 are different, use the keyway in the cartridge to identify the magnetic tape. By using a known mechanical or optical method to detect the presence or absence of a keyway that complies with the above standards and switching the control voltage, the power supply can be turned on and off simply by inserting and removing the above cartridge. can be achieved.

As described above, the present invention is directed to a magnetic reproducing device that uses a magnetic head to reproduce a modulated signal from a magnetic recording medium in which information is recorded by frequency modulation, in which resonance is achieved by electrically connecting the trimmer capacitor for adjustment. A fixed capacitor consisting of a capacitance of a predetermined value that changes the point, and a control signal corresponding to at least one of the maximum frequency deviation or center frequency of the signal recorded on the magnetic recording medium electrically connect the fixed capacitor to a trimmer capacitor for adjustment. Since a switching element is provided to connect or electrically disconnect the capacitor, the capacitance value of the fixed capacitor remains constant and there is no change in capacitance due to temperature, so the total capacitance is also constant and there is no variation in the resonance point. Since the capacitors are electrically connected or disconnected, the movement of each resonance point is ensured, and as a result, even if the modulated signals are reproduced by multiple types of magnetic recording media on which modulated signals with different carrier frequencies are recorded, The above preamplifier can have optimal frequency characteristics according to the carrier frequency of the modulated signal reproduced, and is always in a good state without deteriorating the S/N ratio or exhibiting overmodulation phenomena. This has the effect that the modulated signal can be reproduced by using the following method.

[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 preamplifier, FIG. 2 is a circuit diagram showing an example of the preamplifier which is a feature of the present invention, and FIG. 4 and 4 are circuit diagrams showing other examples of the preamplifier 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, 8 is a fixed capacitor, and 9 is a switching element. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a magnetic reproducing device that uses a magnetic head to reproduce the above-mentioned modulated signal from a magnetic recording medium in which frequency-modulated information is recorded, a matching transformer with a magnetic head connected to a primary coil, and a secondary coil of this matching transformer are used. an adjustment trimmer capacitor connected to the side coil; a fixed capacitor having a predetermined value of capacitance that changes the resonance point by being electrically connected to the adjustment trimmer capacitor;
A control signal corresponding to at least one of the maximum frequency deviation or center frequency of the signal recorded on the magnetic recording medium is input, and this control signal electrically connects the fixed capacitor to the adjustment trimmer capacitor or electrically connects the fixed capacitor to the adjustment trimmer capacitor. 1. A magnetic reproducing device characterized by having a switching element that shuts off.