JPH087202A - Magnetic recording / reproducing device - Google Patents

Abstract

PURPOSE:To eliminate the influence on a recording current and to prevent distortion from occurring in a recorded waveform by sufficiently reducing a resonance frequency due to inductance and a capacitor for cutting off a DC current sufficiently smaller than a low band cut-off frequency in a rotary transformer. CONSTITUTION:Since a signal is supplied to a recording amplifier 103 through the rotary transformer 102, the current I supplied from a current source 301 in an equivalent circuit is provided with a characteristic of low band cut-off. By setting the resonance frequency fp of a low band to 1/3 or below for the low band cut-off frequency fc, the change in the recording current characteristic due to resonance occurs only in a low band attenuation band so that the influence on the whole recording characteristic is not small. Further, in an error rate also, the reduction in the error rate due to the resonance for a ratio of the resonance frequency fp to the low band cut-off frequency fc is prevented by setting the resonance frequency sufficiently lower than the low band cut-off frequency. Thus, the stable error rate is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a video tape recorder (VTR), and more particularly to a signal processing circuit for recording / reproducing a wide band digital signal.

[0002]

2. Description of the Related Art In a VTR for recording / reproducing a wide band signal, a structure in which a recording amplifier is mounted on a cylinder is used in order to suppress a band reduction due to a rotary transformer and a deterioration in transmission efficiency due to a signal loss. An example of this is shown in FIG.
Shown in In FIG. 6, 101 is a recording signal generating circuit, 102 is a rotary transformer, 110 is a rotary cylinder, 103 is a recording amplifier, and 104 is a recording head. The recording head 104 has a terminal at the midpoint of the winding, and this terminal is connected to a power source. The recording amplifier 103 has a differential configuration, and each block is supplied with power from the midpoint terminal of the recording head 104 via the recording head 104. In FIG. 6, the recording signal generated by the recording signal generating circuit 101 is
It is input to the recording amplifier 103 arranged on the rotary cylinder 110 via the rotary transformer 102. The recording amplifier 103 amplifies the recording signal and supplies a recording current to the recording head 104. Here, when the circuits are differentially balanced, the magnetic flux generated by the DC current in the recording head 104 cancels each other out, and therefore the recording current is equivalent to the apparent disappearance of the DC current.

[0003]

However, in the above configuration, since a direct current is actually applied to the recording head during recording, when the differential balance of the circuit is deviated, the recording current is equivalently equivalent to the direct current. An electric current will be generated. This DC current causes distortion in the recording operation of the recording head, which deteriorates the error rate. This is shown in FIG.
In FIG. 7, when a recording current having a waveform of a is input, a magnetic flux having a waveform of b is generated from the head and recorded on the tape when a direct current does not flow. However, when a direct current is flowing through the head, the recording current has a waveform of a ',
The generated magnetic flux has a waveform of b '. Here, when the direct current is large, the head is saturated and a magnetic flux with distortion is generated.
As a result, the recorded signal is distorted and the error rate deteriorates. Also, when the winding balance of the head is deviated, a DC magnetic flux is generated, and the same problem occurs.

In order to solve the above problems, the present invention removes the direct current flowing through the head to prevent distortion from occurring, and
To secure a stable error rate.

[0005]

In order to achieve the above object, the present invention provides a recording amplifier mounted on a rotary cylinder, which is supplied with power via an inductor,
The first feature is that the recording amplifier supplies the recording current to the recording head through the capacitor.

A second feature is that the resonance frequency of the inductor and the capacitor at this time is made sufficiently lower than the low cutoff frequency in the transmission by the rotary transformer.

[0007]

In the present invention, since the power supply to the recording amplifier is supplied from the inductor and both ends of the recording head are connected to the recording amplifier through the capacitors, direct current does not flow in the head and distortion is prevented. You can Also, in the winding of the recording head, it is not necessary to set a terminal in the middle, and the winding structure can be simplified.

Furthermore, by setting the resonance frequency of the inductor and the capacitor sufficiently lower than the transmission band of the rotary transformer, the influence of resonance on the recording current can be prevented and a stable recording state can be secured.
It is possible to stabilize the error rate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention, and the same circuits as those in FIG. 6 are designated by the same reference numerals. In FIG. 1, 105 and 106 are inductors, 107 and 108 are capacitors, and 109 is a recording head. In FIG. 1, the recording signal generated by the recording signal generating circuit 101 is
It is input to the recording amplifier 103 arranged on the rotary cylinder 110 via the rotary transformer 102 and amplified. here,
The output stage of the recording amplifier 103 is composed of an open collector as shown in FIG. In FIG. 2, 201 and 202 are amplifiers, and 203 and 204 are output transistors. In FIG. 2, the input recording signal is amplified by amplifiers 201 and 202 and supplied to output transistors 203 and 204. Power is supplied to the output transistors 203 and 204 from a load connected to the collector, and the output transistors 203 and 204 operate so that a recording current corresponding to a recording signal is passed through the load. Here, in FIG. 1, the loads are the inductors 105 and 106, the capacitors 107 and 108, and the recording head 109, and since the power source is direct current, they are not supplied via the capacitors 107 and 108 and the recording head 109, and the inductors 1
Delivered via 05, 106 only. That is, the recording head 109
DC current does not flow into the recording head 109, so that the distortion of the magnetic flux generated in the recording head 109 due to the deviation of the differential balance of the circuit is not generated. Therefore, the waveform distortion can be prevented and the circuit adjustment can be simplified. In addition, the recording head 109 does not need a midpoint for supplying power, and
The winding structure can be simplified.

Next, the recording current flowing through the recording head 109 in FIG. 1 will be described. Figure 3 shows the equivalent circuit at this time.
Shown in In FIG. 3, 301 is a current source corresponding to the recording amplifier 103, 302 is an inductor, 303 is a capacitor, and 304.
Is a recording head. Here, the inductance of the inductor 302 is 2L, where L is the inductance of the inductors 105 and 106 in FIG. Also, the capacitor 30
The capacitance value of 3 is C / 2, where C is the capacitance value of the capacitors 107 and 108 in FIG. When the impedance of the recording head 304 is Z, the ratio of the current I supplied from the current source 301 to the current Ih flowing through the recording head 304, that is, the transfer characteristic H is expressed by the following equation.

[0012]

[Equation 1]

This characteristic is shown in FIG. As shown in FIG. 4A, this characteristic has resonance at a low frequency fp (= 1 / (2π√LC)). Further, in FIG. 1, since a signal is supplied to the recording amplifier 103 through the rotary transformer 102, the current I supplied by the current source 301 has a low-frequency cutoff characteristic as shown in FIG. 4B. ing. Here, when the low cutoff frequency is fc, fp in the present invention
Is sufficiently smaller than fc, for example, specifically fp is fc
By setting it to be ⅓ or less, the recording current characteristic transmitted to the recording head 304 becomes the characteristic shown in FIG. In FIG. 4C, the change in the recording current characteristic due to resonance occurs only in the low attenuation range. That is, the signal level in the band in which the amplitude and phase changes due to resonance is low, and it is possible to prevent the recording characteristics from being affected. Also, regarding the error rate, the resonance frequency f is shown in FIG.
The change in the error rate with respect to the ratio of p to the low cutoff frequency fc is shown. From FIG. 5 as well, it is possible to set the resonance frequency sufficiently low (specifically, 1/3 or less) with respect to the low cutoff frequency. It can be seen that the reduction of the error rate due to resonance can be prevented.

[0014]

As described above, according to the present invention, no direct current is passed through the head. Further, by making the resonance frequency of the inductor and the capacitor for cutting off the DC current sufficiently smaller than the low cutoff frequency of the rotary transformer, the influence on the recording current can be eliminated. As a result, the recorded waveform is not distorted, and a stable error rate can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a recording amplifier.

FIG. 3 is an equivalent circuit diagram of a recording circuit.

FIG. 4 is a transmission characteristic diagram of each part.

FIG. 5 is a diagram showing a relationship between a ratio between a resonance frequency and a low cutoff frequency and an error rate.

FIG. 6 is a diagram showing an example of a conventional circuit.

FIG. 7 is a diagram showing an operation of the head.

[Explanation of symbols]

102 ... Rotary transformer, 103 ... Recording amplifier, 105,106 ...
Inductors, 107, 108 ... Capacitors, 109 ... Recording heads, 110 ... Rotating cylinders, 203, 204 ... Output transistors.

Claims (3)

[Claims] 1. A magnetic recording / reproducing apparatus having a recording amplifier mounted on a rotary cylinder, wherein a rotary transformer for transmitting a recording signal to the recording amplifier and a recording signal amplified by the recording amplifier are converted into magnetic flux. A magnetic head is provided, an inductor is connected between the collector terminal of the output transistor, which is the output terminal of the recording amplifier, and the power supply, and a capacitor is connected between the output terminal and the magnetic head. A magnetic recording / reproducing apparatus characterized in that a direct current is cut off from the head through the capacitor to supply a recording current so that no direct current flows through the magnetic head. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the resonance frequency generated by the inductor and the capacitor is set lower than the low cutoff frequency in the transmission characteristic of the rotary transformer. 3. The resonance frequency is set to be ⅓ or less of the low cutoff frequency.
Or the magnetic recording / reproducing apparatus according to 2.