JPH07296504A - Reproduction muting circuit and magnetic reproducing device - Google Patents

Abstract

PURPOSE:To provide a reproduction muting circuit capable of shortening a return time to a normal operation state after muting is released and a magnetic reproduction device using it. CONSTITUTION:In the reproductive muting circuit in a circuit for amplifying a signal reproduced from a recording medium through magnetic heads 1A, 1B, short-circuiting circuits 12A, 12B for short-circuiting resistors 5A, 5B connected between DC voltage sources 15A, 15B selected by bias voltage values of input side of reproducing amplifiers 4A, 4B and the input terminals of the reproducing amplifiers 4A, 4B during a muting period are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic reproducing device such as a VTR and a reproducing muting circuit thereof.

[0002]

2. Description of the Related Art In a VHS type VTR, there are various reproduction modes such as a two-hour mode and a six-hour mode, and two rotary magnetic heads are provided in each mode. The outputs of these two magnetic heads are guided via a rotary transformer to the individual regenerative amplifiers where they are amplified. By the way, during reproduction by one magnetic head, the signal of the reproduction system connected to the other magnetic head becomes noise, so that the reproduction signal is muted in the unnecessary reproduction system.

FIG. 5 shows a conventional example of such a mute circuit. In FIG. 5, 1A and 1B are a pair of magnetic heads attached to a rotary drum, and their outputs are rotary transformers 2A and 2B. Coupling capacitors 3A, 3
It is applied to the regenerative amplifiers 4A and 4B via B, respectively. The outputs of the reproduction amplifiers 4A and 4B are made into a continuous signal by the switch 6 which switches for each field, and then amplified by the amplifier 7 and led to the output terminal 8. V _O is the voltage source for biasing the regenerative amplifier 4A, 4B input side, 5A, 5B is a resistor.

P is a switching pulse for switching the switch 6. Reference numerals 9A and 9B denote transistors that form a mute circuit, and the bases of the transistors 9A and 9B have a mute pulse P1 synchronized with the switching pulse P.
P2 is given. The mute pulses P1 and P2 are in an inverse relationship with each other.

Now, while the magnetic head 1B is reproducing and scanning the tape, a negative pulse is applied to the base of the transistor 9B and the transistor 9B is turned off. The reproduction signal of the magnetic head 1B is amplified by the reproduction amplifier 4B and then given to the amplifier 7 via the switch 6. On the other hand, in the reproducing system connected to the magnetic head 1A, the transistor 9A
When a positive pulse P1 is applied to the base of the transistor 9
A is turned on, and the input line 10A is fixed at the ground potential. Therefore, the reproduction amplifier 4A is in the mute state.

Next, while the magnetic head 1A is in the state of reproducing and scanning the tape, the switch 6 is switched and the transistor 9A is turned off, and the reproduction signal from the magnetic head 1A is given to the amplifier 4A. At this time, the transistor 9B is turned on, fixing the line 10B at the ground potential. Therefore, the reproduction amplifier 4B is in the mute state.

[0007]

In the above conventional example, the input bias of the regenerative amplifier in the mute state becomes a normal value after the mute is released (that is, it rises from the ground voltage to a predetermined bias voltage) to some extent. There was a drawback that it took time. Therefore, it is not suitable for high-speed switching.

The present invention has been made in view of the above circumstances, and provides a reproduction mute circuit and a magnetic reproduction apparatus using the same, in which the recovery time to the normal operation state after mute release is shortened. The purpose is to do.

[0009]

In order to achieve the above object, according to the present invention, in a reproducing muting circuit in a circuit for amplifying a signal reproduced from a recording medium, the bias voltage value on the input side of the reproducing amplifier is selected. And a means for short-circuiting the resistor connected between the DC voltage source for applying the above voltage and the input terminal of the regenerative amplifier during the mute period.

Further, according to the present invention, in the magnetic reproducing apparatus, the outputs of the first and second amplifiers for individually amplifying the reproduction output signals of the two magnetic heads are alternately switched at regular intervals to obtain a continuous reproduction signal. , The reproduction muting circuit is provided for the first and second amplifiers, and the two muting circuits are alternately operated at the constant period. At that time, a plurality of groups each including the two magnetic heads, two amplifiers, and two reproduction mute circuits are provided, and two reproduction mute circuits that are not used between the different groups are put into a mute operation state and used. The two reproduction mute circuits of the set are alternately operated at the constant period.

[0011]

[Operation] According to such a reproduction muting circuit,
During the mute period, the input terminal of the regenerative amplifier is fixed to the bias voltage during the steady operation, so that the steady operating state of the regenerative amplifier after the mute release can be immediately obtained. Also,
According to the magnetic reproducing apparatus of the second or third aspect equipped with the reproducing muting circuit, crosstalk between channels is small and a high-quality reproduced signal can be obtained.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1 in which the present invention is implemented, the same parts as those in FIG. 1
Reference numeral 1 indicates a semiconductor integrated circuit chip. The regenerative muting circuit of this embodiment includes regenerative amplifiers 4A and 4A.
The resistors 5A and 5B connected between the DC voltage sources 15A and 15B that provide the selected bias voltage V ₁ on the input side of B and the input terminals of the regenerative amplifiers 4A and 4B are short-circuited (short-circuited) during the mute period. ) Short circuit 12A, 12B
Is provided. When one of the short-circuiting circuits 12A and 12B is in operation, the other is inoperative.

FIG. 2 shows the details of the short-circuiting circuit 12A (12B), and Q1 is a transistor constituting the regenerative amplifier 4A (4B). Q2 and Q3 form a bidirectional switch whose emitter and collector are connected to each other,
When a mute pulse (positive pulse) is applied to their bases via the current limiting resistors R ₂ and R ₃ , it turns on and the resistor 5 is turned on.
Short circuit. Due to this short circuit, the input terminal of the regenerative amplifier is fixed to the voltage V ₁ during the mute period. When the bidirectional switch (transistors Q2 and Q3) is turned off after the mute period ends, the base voltage of the transistor Q1 is the voltage V ₁ and the transistor Q1 is in a normal amplification state. As described above, in the present embodiment, the return to the normal amplification state after the mute release is very fast.

FIG. 3 shows the structure of a reproducing system when the reproducing mute circuit is applied to a VTR having four heads. In the figure, 31A and 31B are two-hour mode magnetic heads, and 41A and 41B are six-hour mode magnetic heads. The reproducing circuit and the reproducing muting circuit connected to each head have the same configuration as shown in FIG.

For example, when reproducing the head 31A, a reproduction amplifier 34A, a DC power supply 37A, a resistor 38A, and a short-circuit switch 39A are provided, and the output terminal thereof is connected to one contact 35A of the switch 50. Hereinafter, the head 31B,
The circuit configurations of 41A and 41B are similar. Here, the short circuit switches 39A, 39B, 49A,
49B represents the short-circuiting circuit shown in FIGS.
The switch 50 switches every field. The same applies to the switch 51. The switch 54 is switched between the 2-hour mode and the 6-hour mode.

Here, the short-circuit switches 39A, 39B, 4
The operation of 9A and 49B will be described. Now, assuming that the 2-hour mode is being played back, the 6-hour mode short-circuit switch 49
A and 49B are both turned on, and heads 41A and 4A
Mutes the signal from 1B. On the other hand, the 2-hour mode mute switches 39A and 39B are alternately turned on and off for each field. That is, when the head 31A is reproducing, the mute switch 39A is OFF, the mute switch 39B is ON, and in the next field, the mute switch 39A is ON and 39B is OFF.

In FIG. 3, on the output side of the switch 54, luminance signal system circuits 55 to 61 and color signal system circuits 62 to 6 are provided.
After 6 is connected and the luminance signal and the chrominance signal are individually processed, they are combined by the adder 67 and given to the video processing circuit 68. Since these circuits are well known, the description thereof will be omitted.

FIG. 4 shows a VT equipped with four heads as shown in FIG.
The rotary transformer portion of R is shown, and (a) shows the surface of the rotor 72 facing the stator 71. Both the stator 71 and the rotor 72 are provided with circular grooves in their facing surfaces, and the coils (wires) 73 are buried in the grooves, but since they are close to each other, not only between corresponding coils but also other coils. Magnetic coupling also occurs between and. However,
Crosstalk can be sufficiently prevented by adopting the muting configuration described in FIG.

It should be noted that in recent VTRs, there has been a model equipped with not only such four heads but also a head dedicated to reproduction for 6 hours, a head dedicated to hi-fi, etc. Since it is the same as in the case of four heads, the coils of the rotary transformer become closer to each other, and the influence of crosstalk between the coils becomes large. However, by adopting the muting method as in this embodiment, it is possible to obtain a high quality video signal with less crosstalk.

[0020]

According to the regenerative muting circuit of the present invention, the rise of the regenerative amplifier to the steady operation state after mute release is accelerated. Further, in the magnetic reproducing apparatus according to the second or third aspect, in which the reproducing muting circuit is mounted, crosstalk between channels is small and a high-quality reproduced signal can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a reproducing muting circuit embodying the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of a part thereof.

[Figure 3] VTR equipped with the playback muting circuit
Circuit diagram of the playback system.

FIG. 4 is a diagram showing a rotary transformer portion of the VTR.

FIG. 5 is a circuit diagram showing a conventional reproduction muting circuit.

[Explanation of Codes] 1A, 1B Magnetic heads 2A, 2B Rotary transformer 4A, 4B Regenerative amplifier (first stage regenerative amplifier) 5A, 5B Resistors 12A, 12B Short circuit 15A, 15B DC voltage source

Claims (3)

[Claims] 1. A reproducing muting circuit in a circuit for amplifying a signal reproduced from a recording medium, wherein a direct current voltage source for applying a selected voltage to a bias voltage value on the input side of the reproducing amplifier and an input terminal of the reproducing amplifier. A reproducing muting circuit comprising means for short-circuiting a resistor connected between the two during a mute period. 2. A magnetic reproducing apparatus for obtaining continuous reproduced signals by alternately switching outputs of first and second amplifiers for individually amplifying reproduced output signals of two magnetic heads at regular intervals. The reproduction muting circuit described in 1.
A magnetic reproducing apparatus provided with respect to a second amplifier, wherein the two muting circuits are alternately operated at the fixed period. 3. The two magnetic heads, two amplifiers, and two.
A plurality of sets each including one reproduction mute circuit are provided. Two sets of the reproduction mute circuits that are not used between the different sets are set to the mute operation state, and the two reproduction mute circuits of the set that are used are alternately arranged at the predetermined period. The magnetic reproducing apparatus according to claim 2, wherein the magnetic reproducing apparatus is made to operate.