JPH0744673B2 - Recording / playback switching circuit - Google Patents

Description

The present invention relates to a VTR (video tape recorder) recording / playback switching circuit, and in particular, noise caused by a tape head switching switch is recorded on a tape. The present invention relates to a recording / reproducing switching circuit for preventing the above.

(B) Conventional technology In a VTR in which a single magnetic head is used for both recording and reproduction, a tape head changeover switch for changing over the magnetic head is provided, and the changeover control of the switch is performed according to the recording or reproduction operation. Need to do. Also a normal VTR
In the above, an AC bias circuit for supplying an AC bias to the magnetic head at the time of recording is provided, and control is performed so that the AC bias circuit is operated only at the time of recording. In such a VTR, when the tape head changeover switch is switched while the oscillation of the AC bias circuit is in a transient state, noise generated at the time of switching is recorded on the tape. In order to prevent this, conventionally, the tape head changeover switch is always set to the recording state except during reproduction, and the tape head changeover switch is prevented from being changed over at the start of the recording operation. "85 Sanyo Semiconductor Handbook Monolithic Bipolar Integrated Circuit Edition" (Published March 20, 1985) Page 965 describes an application circuit example of IC (integrated circuit) LA7090 for voice recording / playback amplifier. A recording / reproducing switching circuit as shown in FIG. 4 is shown therein. In FIG. 4, when the VTR is switched to the recording state, the "H" signal is applied to the recording control terminal (1) and the "L" signal is applied to the terminal (2). The "H" signal is applied to the AC bias circuit (4) via the drive circuit ( 3 ) to operate the AC bias circuit (4). Therefore, AC bias circuit (4)
Is superimposed on the output signal of the recording amplifier (5) and applied to the tape head (6). At that time, since the "L" signal is applied to the terminal (2), the switch (7) is on, the switch (8) is off, and one end A of the tape head (6) is grounded.

Next, when the VTR is stopped, the "L" signal is applied to the recording control terminal (1), the drive circuit ( 3 ) stops its operation, and the oscillation of the AC bias circuit (4) stops. At this time, the states of the switches (7) and (8) do not change. Next, when you change the VTR from the stopped state to the playback state,
The "H" signal is applied to the terminal (2), the switches (7) and (8) are switched to the states opposite to those shown in the figure, the end A of the tape head (6) is released from the ground, and the tape head (6) is released. 2) is grounded. Therefore, the reproduction signal from the tape head (6) is applied to the reproduction amplifier (9) and amplified by the reproduction amplifier (9).

Therefore, according to the circuit of FIG. 4, since the switches (7) and (8) are not switched at the start of recording, noise is not recorded on the tape.

(C) Problems to be Solved by the Invention However, in the recording / reproducing switching circuit as shown in FIG. 4, the switches (7) and (8) are switched according to the reproducing operation according to the generated signal. Since the switch for controlling the operation of the AC bias circuit (4) is switched by the signal generated according to the recording operation,
It requires two control systems, and has the drawback of increasing the number of external parts and the number of pins when making an IC.

Further, as shown in FIG. 4, the conventional recording / reproducing switching circuit can incorporate a changeover switch (switch (8)) requiring a high breakdown voltage process into an IC made by a low noise process for signal processing. Since it does not exist, there is a problem that two IC chips are required, which makes circuit design troublesome.

(D) Means for Solving the Problems The present invention has been made in view of the above points, and includes a magnetic head for recording / reproducing, a bias circuit for supplying an AC bias to the magnetic head, A first switch for controlling the operation of the bias circuit, a second switch for grounding one end of the magnetic head at the time of recording, a third switch for grounding one end of the magnetic head at the time of reproduction, and a third switch for generating a recording start operation. It comprises an input terminal to which a control signal is applied, and a control circuit which is connected to the input terminal and generates a control signal for switching the first to third switches.

(E) Operation According to the present invention, the tape head changeover switch and the AC bias circuit can be changed over only by the recording control signal. Further, it is possible to form only the tape head changeover switch requiring the high withstand voltage process with another pellet and mold the pellet with the pellet for the signal processing circuit as a single IC.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. (10) is an input terminal to which a recording control signal is applied, ( 11 )
Is a delay circuit for delaying the recording control signal from the input terminal (10), and (12) generates a control signal according to the voltage of the control pin (13) to which the output signal of the delay circuit ( 11 ) is applied. Control circuit, (14) AC bias circuit, (1
5) is a first switch for operating the AC bias circuit (14) according to a control signal from the control circuit (12), (16) is a recording amplifier, (17) is a reproducing amplifier, (18) is a tape head, (19) responds to the control signal from the control circuit (12),
A second switch that turns on during recording and turns off during playback,
Reference numeral (20) is a third switch which is turned off during recording and turned on during reproduction according to a control signal from the control circuit (12).
In addition, (21) is a voice recording / reproducing IC, and the third switch (20)
Only the other is formed on a pellet and the other circuits are molded together in one package with the pellet.

Next, the operation will be described. When the VTR is stopped, the recording control signal is not applied to the input terminal (10) and the voltage at the control pin (13) is zero. In that state, the first switch (15) is off and the second switch (19) is
Is off and the third switch (20) is on.

Next, when a recording control signal is applied to the input terminal (10), the voltage of the control pin (13) gradually rises as shown in FIG. When the voltage of the control pin (13) rises to V ₁ at time t ₁ , the second switch (19) is turned on according to the output signal of the control circuit (12), and at time t ₂ the control pin (13) is turned on. The third switch (20) is turned off when the voltage rises to V ₂ .
For this reason, the changeover switch (second and third switches (19) and (20)) of the tape head (18) is prepared for recording, and the voltage of the control pin (13) becomes V ₃ at time t ₃ and control is performed. Even if the first switch (15) is turned on by the output signal of the circuit (12), noise due to the switching of the switching switch is not recorded on the tape. First switch (15) at time t ₃
When is turned on, the AC bias circuit (14) starts oscillating, the AC bias signal and the audio signal from the recording amplifier (16) are superimposed, and applied to the tape head (18).

Next, the operation when the VTR is switched from the recording state to the stopped state will be described. When the stop operation is performed, the recording control signal stops and the voltage at the control pin (13) decreases as shown in FIG. When the VTR in the recording state is stopped at time t ₀ , the voltage on the control pin (13) is delayed by the delay circuit ( 11 ).
The capacitor is discharged and gradually decreases. When the voltage of the control pin (13) drops to V _{3 at} time t ₁ , the output signal of the control circuit (12) turns off the first switch (15),
The oscillation of the AC bias circuit (14) stops. When the voltage of the control pin (13) drops to V _{2 at} time t ₂ , the output signal of the control circuit (12) turns on the third switch (20), and when it drops to V _{1 at} time t ₃ , the second The switch (19) turns off. Therefore, the noise generated by switching the changeover switch is not recorded on the tape.

In FIG. 1, the second switch (19) is off and the third switch (20) is on in the stopped state. The state of this switch is the same as the state of the switch at the time of reproduction, and when changing from the stopped state to the reproduction state, there is no need to operate the changeover switch, and the control signal for reproduction becomes unnecessary. Conventionally, the changeover switch is a high voltage IC
Since the second switch (19) was originally formed inside, the high withstand voltage up to the second switch (19), which originally does not need to be high withstand voltage, is formed on the pellet for voice recording / reproduction. As a result, only the third switch (20), which requires a high withstand voltage process, can be formed by another pellet, and both pellets can be molded as a single IC, and recording / reproduction switching can be performed by only a single IC. .

(G) Effect of the Invention According to the present invention, the control of the tape head changeover switch can be performed only by the recording control signal.
It is possible to reduce the number of pins and the number of external parts at the time of commercialization. Also, as in the example, if the pellets for switches created by the high withstand voltage process and the pellets for signal processing created by the low noise process are molded in a single IC, the handling becomes very easy and the VTR circuit Design becomes easy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 and 3 are characteristic diagrams for explaining FIG. 1, and FIG. 4 is a circuit diagram showing a conventional recording / reproducing switching circuit. Is. (10) …… Input terminal, ( 11 ) …… Delay circuit, (12) ……
Control circuit, (14) ... AC bias circuit, (15) ... first switch, (18) ... tape head, (19) ... second
Switch, (20) …… The third switch.

Claims (1)

[Claims] 1. A magnetic head for recording and reproducing, a bias circuit for supplying an AC bias to the magnetic head, a first switch for controlling the operation of the bias circuit, and one end of the magnetic head grounded during recording. And a third switch for grounding the other end of the magnetic head during reproduction,
The control signal from the control circuit is composed of an input terminal to which a control signal indicating recording time is applied, and a control circuit connected to the input terminal to generate a control signal for switching the first to third switches. Accordingly, at the start of recording, first the second and third switches are switched, and then the first switch is switched to operate the bias circuit, and when the recording is stopped, the first switch is switched to stop the operation of the bias circuit. A recording / reproducing switching circuit characterized in that the second and third switches are switched after that.