JP3988290B2 - Signal reproduction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal reproducing apparatus that reproduces signals having different band characteristics on electromagnetic conversion recorded on a magnetic recording medium using the same head and rotary transformer.
[0002]
[Prior art]
Conventionally, for example, when reproducing a signal recorded on a magnetic tape, the head and the rotary transformer are optimized in accordance with the signal form (format) on electromagnetic conversion required for reproducing the signal. It has been decided.
[0003]
Therefore, when reproducing signals on electromagnetic conversion with different required band characteristics, such as a wideband digital signal and a narrowband analog signal, for example, each of the digital signal and the analog signal is dedicated to each signal form. The reproducing head and the rotary transformer are used. In this case, the rotary transformer is multi-channeled corresponding to the digital signal and the analog signal.
[0004]
[Problems to be solved by the invention]
However, as described above, for the purpose of reproducing signals on electromagnetic conversion having different required band characteristics, providing a plurality of dedicated reproducing heads or increasing the number of rotary transformers increases the cost. At the same time, the size of the structure increases. That is, for example, when a dedicated reproduction head corresponding to each of the digital signal and the analog signal is provided and a corresponding rotary transformer is provided, the cost and configuration are compared with the configuration in which only one of the signals is reproduced. Will be more than twice.
[0005]
In addition, for example, a digital recording / reproducing apparatus having upward compatibility (in this case, the upper function is digital recording / reproduction) that performs recording / reproduction of a digital signal in a normal state but can reproduce only a conventional analog signal. If it is considered to constitute, the cost increase and the increase in the size of the structure as described above are a heavy burden.
[0006]
On the other hand, using the same head and rotary transformer to reproduce signals on electromagnetic conversion with different required band characteristics, for example, using a head and rotary transformer optimized for a certain signal format (format) If an attempt is made to reproduce the signal, the C / N deteriorates when a signal having a form other than the optimum signal form is reproduced. Of course, when a head and a rotary transformer that are not optimized for any signal form are used, C / N deteriorates when signals of all signal forms are reproduced.
[0007]
Therefore, the present invention has been made in view of such circumstances, and signals on electromagnetic conversion having different required band characteristics can be satisfactorily used (improvement of C / N) using the same head and rotary transformer. An object of the present invention is to provide a signal reproducing apparatus that can be reproduced and that can prevent an increase in cost and an increase in configuration.
[0008]
[Means for Solving the Problems]
According to the present invention, there is provided a signal reproducing apparatus for reproducing at least a signal having different band characteristics on electromagnetic conversion from a magnetic recording medium using the same magnetic head and rotary transformer, and an equivalent inductance of the magnetic head and the rotary transformer. Resonance frequency determined from the resonance capacitance, the resonance frequency changing means for changing or switching according to the form of the signal having different band characteristics on the electromagnetic conversion, and a feedback loop for damping the resonance frequency, And a variable gain differential amplifier for amplifying the output of the resonance frequency changing means. The resonance frequency changing means includes a first capacitor connected between the first terminal and the second terminal of the rotary transformer, and a second capacitor having one terminal connected to the first terminal of the rotary transformer. A capacitor having the same capacity as the second capacitor, one terminal of which is connected to the second terminal of the rotary transformer, and the other terminal of the second capacitor is grounded A first transistor; and a second transistor for grounding the other terminal of the third capacitor. Then, the on / off of the first and second transistors and the gain of the feedback loop of the variable gain differential amplifier are switched according to the form of a signal having different band characteristics on the electromagnetic conversion.
[0009]
That is, according to the present invention, for example, when signals on electromagnetic conversion having different required band characteristics, such as digital signals or analog signals, are reproduced using the same magnetic head and rotary transformer, the signal forms of these different bands are used. The C / N and amplitude characteristics are optimized in each band by changing or switching the resonance frequency and the amount of damping according to the frequency.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described with reference to the drawings.
[0011]
As a configuration of the main part of a magnetic recording / reproducing apparatus serving as a reference example of the signal reproducing apparatus of the present invention, FIG. 1 shows a configuration of a magnetic head 1 and a rotary transformer 2 (FIG. 1A) and its equivalent circuit (FIG. 1). FIG. 2 shows the head 1, rotary transformer 2 (head rotary system 3), amplifier 5, control circuit 6, resonance capacitance (Ct), and the like. Yes.
[0012]
The basic functions of a magnetic recording / reproducing apparatus serving as a reference example of the present invention will be described below with reference to FIGS. It will be described later concrete description of the operation of the magnetic recording and reproducing apparatus.
[0013]
As an example, the band for electromagnetic conversion in the head rotary system 3 required at the time of digital recording / reproduction requires a band of 20 MHz or more when the recording wavelength is about 0.49 μm, for example. On the other hand, the required bandwidth in the head rotary system 3 required at the time of analog recording / reproducing is, for example, a so-called high-band type 8 mm video format, which is 10 MHz or less even at the tip of the white clip.
[0014]
In addition, the head resonance frequency ω ₀ generated in the transmission frequency characteristics of the head rotary system 3 is generally placed at the upper limit of the required band, and is damped (brake) so that the C / N and amplitude phase characteristics are optimized. . Therefore, the transmission band of the head rotary system 3 is up to the resonance frequency ω ₀ .
[0015]
Further, the head resonance frequency ω ₀ is Lt as an inductance (equivalent conversion inductance of the head rotary system) viewed from the entrance of the head amplifier 5 to the head rotary system 3 side, Lr is an inductance on the rotor side of the rotary transformer 2, and the stator Ls is the inductance on the side, n is the turn ratio of the rotary transformer 2, k is the coupling coefficient, Lh is the head inductance, and Ct (Ct = Ci + Cs) is the total capacity (resonance capacity) including the other inputs of the harness and the amplifier 5. For the sake of simplicity, when the approximate resistance is ignored (Rh = Rs = 0), the following equation is obtained.
[0016]
Lt = n ² * Lr {1-Lrk ² / (Lr + Lh)}
ω ₀ = I / √ (LtCt)
Taking a so-called 8 mm video as an example of the signal form (format), the turn ratio n of the rotary transformer is 2 to 5. For example, if it is intended to realize a wide band (digitalization) of at least twice the turn ratio n for this 8 mm video format, the turn ratio n becomes 2 to 3. In addition, when performing a wide band more than twice with the turn ratio n, the turn ratio n is 2 to 3 because only an integer ratio is allowed for the turn ratio n. Further, when the resonance capacitance Ct is improved, the head resonance frequency ω ₀ is approximately doubled. In the system configured as described above, for example, only when a wide band signal (digital signal) is used, if the relative speed of the tape and the head is set to at least twice that when reproducing a narrow band signal (analog signal). Thus, a recording / reproducing apparatus for a broadband signal (digital signal) can be easily realized.
[0017]
However, in such a recording / reproducing apparatus, for example, when a conventional narrow-band signal (analog signal) is reproduced, the input signal level to the amplifier 5 is about −4.4 dB compared to the conventional art due to the decrease in the turn ratio n. Will be reduced. If it is left as it is, it is easily affected by amplifier noise or the like in the vicinity of the reproduction limit frequency, which is disadvantageous in terms of C / N and causes image quality degradation.
[0018]
Here, if the gain (gain) of the feedback loop of the amplifier 5 is Ka and the input equivalent equivalent noise resistance is r, the head rotary system 3 can be approximated as shown in FIG. Incidentally, the resistor R in the figure is a resistor for feeding back and damping the head resonance frequency.
[0019]
As a result, the input-converted total noise _eth of this system is expressed by the following equation when the measurement bandwidth is 1 Hz. Note that Rh = Rs = 0.
[0020]
e ² _th = 4 kT {(1-ω ² LtCt) ² (r + r ² / R) + (ωLt) ² / R}
In this equation, k is a Boltzmann constant and T is an absolute temperature. In addition, the inside of {} in this equation is the total resistance of the input equivalent equivalent noise. Further, the first term of the equation represents a noise source from the amplifier 5, and the second term represents a noise source from the damping resistor R. However, the input equivalent equivalent noise resistance r in FIG. 2 is not included in the transfer function.
[0021]
From this equation, it can be seen that the influence of the amplifier noise source is minimized at the head resonance frequency ω = ω ₀ . That is, if the head resonance frequency is shifted according to a wideband signal (digital signal) or a narrowband signal (analog signal), the C / N at the target reproduction limit frequency is the respective reproduction band. It can be seen that it can be effectively improved. Although the detailed configuration will be described later, it can be seen that the cost required for this is very small like the control unit 6 in FIG.
[0022]
Next, the value of the optimum damping resistance R for obtaining a good amplitude phase characteristic in transmission is given by the following equation.
[0023]
R = (1 + Ka) * √ (Lt / 2Ct)
In this equation, when the gain Ka of the feedback loop of the amplifier 5 is set to 0, the non-feedback state is represented. However, as the gain Ka of the feedback loop increases, a large damping resistance value can be used. It can be seen that the larger the resistance value of the damping resistor R, the more effective the C / N improvement.
[0024]
By the way, when signals having different reproduction bands such as a narrow band signal (analog signal) and a wide band signal (digital signal) are reproduced by the same head rotary system 3, the resonance frequency Ct is controlled by operating the resonance capacitor Ct. Although the C / N is improved by shifting, distortion is accompanied if the value of the damping resistance R that provides the optimum amplitude phase characteristic is not changed, as can be seen from the above formula.
[0025]
However, the damping resistor R has a fixed value because it is a resistor built in the amplifier 5 (IC). On the other hand, even if the damping resistance R is a fixed value, it can be understood that the above equation can be easily established by manipulating the gain Ka of the feedback loop of the amplifier 5 corresponding to the change of the resonance capacitance Ct. In other words, when reproducing a narrow band signal (analog signal), the amplitude phase characteristic can be optimized by increasing the resonance capacitance Ct to lower the head resonance frequency and at the same time increase the gain Ka of the feedback loop. it can. In this case, it is clear that C / N does not change even if the amplitude phase characteristic is arbitrarily manipulated because the damping resistance R is a fixed value.
[0026]
In FIG. 2, the control unit 6 controls the resonance capacitor Ct and the gain Ka of the feedback loop, thereby realizing the optimum amplitude phase characteristic as described above.
[0027]
Hereinafter, the configuration of FIG. 2 will be described.
[0028]
In FIG. 2, for example, a signal voltage induced in the head 1 by reproducing a magnetic tape is multiplied by n by the rotary transformer 2 to become V1. The signal of the signal voltage V 1 passes through a low-pass filter formed by the equivalent conversion inductance Lt of the head rotary system 3 and its resonance capacitance Ct, and is input to the amplifier 5.
[0029]
A so-called head resonance frequency generated by the low-pass filter is output through an amplifier 53 having a gain K3, with its amplitude and phase characteristics corrected by a feedback loop formed by a gain Ka of the feedback loop, a damping resistor R, and a capacitor Cf.
[0030]
The gain Ka of the feedback loop is determined by the multiplication value (Ka = K1 * K2) of the gains K1 and K2 of the amplifier 51 and its inverting amplifier 52. The gain K2 constituting the gain Ka of the feedback loop is determined by the control unit 6. Is controlled by a gain control signal gc. For example, when the voltage value of the gain control signal gc decreases, the gain K2 increases, that is, the feedback loop gain Ka increases.
[0031]
The voltage value of the gain control signal gc is set by the resistors R7, R8, R6 in the control unit 6, and whether or not the gain control signal gc having the set voltage value is supplied to the amplifier 52 of the amplifier 5 is determined by a transistor. It is controlled by turning on / off Q4.
[0032]
The resonance capacitance Ct is determined by the capacitors Ci and Cs (Ct = Ci + Cs). Of the capacitances Ci and Cs for determining the resonance capacitance Ct, for example, the capacitance Cs has the head resonance frequency. This is an additional capacitor for lowering the head resonance frequency by increasing the resonance capacitor Ct.
[0033]
Whether or not the additional capacitor Cs is used is controlled by the transistors Q1 and R2, Q2 and R2, and Q3 of the control unit 6 so as not to affect the recording. For example, when the resonance frequency Ct is increased to lower the head resonance frequency, the transistors Q1 to Q3 are controlled to be turned on.
[0034]
Further, a transistor Q4 for selecting whether or not to perform control for increasing the gain K2 of the feedback loop, and a transistor Q3 for selecting whether or not to increase the resonance capacity Ct (control the additional capacity Cs) ( The operations with Q1-Q3) are on / off controlled by the mode control signal mc.
[0035]
The mode control signal mc is a signal determined in accordance with the form of a signal having different band characteristics on electromagnetic conversion, that is, in the case of the present embodiment, the signal to be reproduced is, for example, a wideband signal (digital signal). Alternatively, the signal is determined according to whether the signal is a narrow band signal (analog signal), and is set to a low (L) level during recording and reproduction of a wide band signal (digital signal), and the narrow band signal (analog signal) At the time of reproduction, it is set to a high (H) level.
[0036]
For example, when the mode control signal mc is set to a low (L) level during recording / reproduction of a wideband signal (digital signal), the transistors Q3 to Q1 and the transistor Q4 are turned off (open). On the other hand, when the mode control signal mc is set to a high (H) level during reproduction of a narrow band signal (analog signal), the transistors Q3 to Q1 and the transistor Q4 are turned on.
[0037]
Thus, when the mode control signal mc becomes high level, the transistors Q3 to Q1 are turned on, the head resonance frequency is lowered by the additional capacitor Cs of the resonance capacitor Ct, and at the same time, the transistor Q4 is turned on and the voltage of the gain control signal gc is changed. As a result, the gain Ka of the feedback loop increases, and the amplitude phase characteristic is corrected so as to be optimized.
[0038]
The example of FIG. 2 is a circuit example corresponding to one channel in which the output of the head rotary system 3 is unbalanced. However, in the case of multiple channels, the configuration may be the same as in FIG.
[0039]
Next, FIG. 3 shows a circuit configuration example corresponding to one channel in which the output of the head rotary system 3 of the present invention is balanced. In general, balanced input processing is strong against the removal of in-phase unnecessary signals. In FIG. 3, the same constituent elements (each element and the like) as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description of overlapping parts is omitted. Although FIG. 3 also shows the recording amplifier 11 at the same time, the description thereof is omitted.
[0040]
In the configuration example of FIG. 3, a differential amplifier 21 is used as an amplifier (reproduction amplifier 12) in order to perform a balancing process. The gain of the differential amplifier 21 is controlled by the same gain control signal gc as in FIG. That is, the voltage value of the gain control signal gc is set by the resistors R7, R8, R6 in the control unit 13, and whether the gain control signal gc having the set voltage value is supplied to the inverting amplifier 52 of the reproduction amplifier 12. No is controlled by turning on / off the transistor Q4. The gain of the inverting amplifier 52 is controlled by a gain control signal gc from the control unit 13.
[0041]
Further, in the configuration example of FIG. 3, in order to perform the balancing process, the additional capacitor constituting the resonance capacitor Ct is set to 2Cs, and two capacitors for this additional capacitor 2Cs are prepared. In order to use these two additional capacitors 2Cs, a transistor Q5 is newly added to the control unit 13 for controlling the newly added additional capacitor 2Cs, and processing is performed so as not to break the balance. These additional capacitors 2Cs are equivalent to the additional capacitors in FIG.
[0042]
In the configuration of FIG. 3, at the time of recording, the reproduction amplifier 12 is turned off, and the control unit 13 sets the mode control signal mc to a low level so that the transistors Q1, Q5 and Q4 are turned off (open). Thereby, recording is performed by the recording amplifier 11. On the other hand, the reproduction amplifier 12 is turned on during reproduction, and the mode control signal mc is set to a low level so that the transistors Q1, Q5, and Q4 are turned off by the control unit 13 during reproduction of a wideband signal (digital signal), for example. For example, when reproducing a narrow-band signal (analog signal), the control unit 13 sets the mode control signal mc to high level so that the transistors Q1, Q5, and Q4 are turned on.
[0043]
In this way, the C / N at the time of reproduction of a narrow band signal (analog signal, in this embodiment, 8 mm video format) with a minimum additional circuit for the recording and reproduction system of the wide band signal (digital signal). It has improved.
[0044]
Next, FIG. 4 shows a characteristic diagram at the time of signal reproduction in the magnetic recording / reproducing apparatus of the present embodiment. In FIG. 4, as an example, Rh = 13, Rs = 1, r = 12, Ls = 3.59 μH, Lh = 1 μH, n = 1.5, K = 0.95, R = 30k, Ci = 25 pF, Cs = 68 pF, Ct = Ci represents the input conversion noise dBm / √ (Hz) when reproducing the wideband signal, and Ct = Ci + Cs represents the narrowband signal.
[0045]
From FIG. 4, it can be seen that according to the present embodiment, the C / N in the vicinity of 10 MHz is improved by 1.3 dB at the time of reproducing the narrow band signal.
[0046]
As described above, for example, when a wide band signal (digital signal) or a narrower band signal (analog signal) is reproduced by a head rotary system, a combination of a wide and narrow band dedicated head and a multi-channel rotary transformer is used. If realized, the material cost, new design, etc. will be a significant cost increase factor, and the device cannot be provided at a low cost. However, in the embodiment of the present invention, a so-called conventional rotary transformer is widened without providing a new channel. The optimization of the C / N and amplitude / phase characteristics of the desired wide / narrow transmission characteristics is realized only by switching the external additional capacity and the gain of the feedback loop for damping correction. The circuit configuration is simplified and the influence on the broadband circuit is eliminated. It has become a reproducible narrow band signal as an upper compatibility (analog signal) by a simple and inexpensive configuration in the recording and reproducing apparatus of the digital signal).
[0047]
【The invention's effect】
As is clear from the above description, in the signal reproducing apparatus of the present invention, the resonance frequency determined from the equivalent inductance and the resonance capacitance of the magnetic head and the rotary transformer is changed to a signal form having different band characteristics on electromagnetic conversion. By changing or switching according to the frequency, the signals on the electromagnetic conversion having different required band characteristics can be reproduced satisfactorily (C / N improvement) using the same magnetic head and rotary transformer. It is possible to prevent an increase in the size and size of the configuration.
[0048]
That is, according to the signal reproducing apparatus of the present invention, when reproducing a wideband signal or a narrower band signal, the same head rotary system can be used without providing a new channel, and the intended wide and narrow range can be used. Achieves optimization of C / N and amplitude / phase characteristics of transmission characteristics, does not increase the circuit configuration, and has no effect on broadband circuits. Furthermore, wideband signal recording / reproducing apparatus has a narrow band as an upward compatible function. Can be reproduced with a simple and inexpensive configuration.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a head and a rotary transformer and their equivalent circuits (head rotary system).
FIG. 2 is a circuit diagram showing a configuration example corresponding to one channel in which the output of the head rotary system is unbalanced.
FIG. 3 is a circuit diagram showing a configuration example corresponding to one channel in which the output of the head rotary system is balanced.
FIG. 4 is a characteristic diagram showing characteristics at the time of signal reproduction in the magnetic recording / reproducing apparatus of the present embodiment.
[Explanation of symbols]
1 head, 2 rotary transformer, 3 head rotary system, 5,12 amplifier, 6,13 control unit

Claims (1)

In a signal reproducing apparatus for reproducing at least a signal having different band characteristics on electromagnetic conversion from a magnetic recording medium using the same magnetic head and rotary transformer,
Resonance frequency changing means for changing or switching the resonance frequency determined from the equivalent inductance and resonance capacitance of the magnetic head and rotary transformer according to the form of the signal having different band characteristics on the electromagnetic conversion;
A feedback loop for damping the resonance frequency, and a variable gain differential amplifier for amplifying the output of the resonance frequency changing means,
The resonance frequency changing means includes a first capacitor connected between the first terminal and the second terminal of the rotary transformer,
A second capacitor having one terminal connected to the first terminal of the rotary transformer;
A third capacitor having the same capacity as the second capacitor and having one terminal connected to the second terminal of the rotary transformer;
A first transistor that grounds the other terminal of the second capacitor;
A second transistor for grounding the other terminal of the third capacitor,
Depending on the form of the band characteristics different signals on the electromagnetic conversion, the signal reproducing apparatus and switches the gain of the feedback loop of the on-off and the variable gain differential amplifier of the first and second transistors.

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