JPH06309612A - Circuit for switching recording and reproducing - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a noise by recording and reproducing a signal on the recording medium of a magnetic tape with a circuit for switching recording and reproducing using a magnetic head. CONSTITUTION:This circuit is provided with a magnetic head coil 1 recording and reproducing the signal on the recording medium, a recording amplifier 2 and a reproducing amplifier 3 connected to one end of the coil 1, an oscillation bias circuit 4 connected to the other end of the coil 1 and a switch 5 stopping the operation of the circuit 4 at a recording time. Further, a control means 6 controlling the amplitude of the AC output signal of the oscillation bias circuit 4 is provided, too. The switches 5, 7 are closed and the switch 8 is opened at a recording time. When the switch 5 is closed, the oscillation bias circuit 4 is started to operate oscillation, and an AC output signal with about 70-80kHz is generated in a primary side coil 9, and then, similar AC output signal is generated from a secondary side coil 10, and flows trough the output end of the recording amplifier 2 through the coil 1. On the other hand, a recording signal from a terminal 11 is amplified 2 and supplied to the magnetic head coil 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing switching circuit for recording / reproducing a signal by using a magnetic head for a recording medium such as a magnetic tape, and more particularly to a recording / reproducing switching circuit for preventing generation of noise. Regarding

[0002]

2. Description of the Related Art In a VTR in which a single magnetic head is used for both recording and reproduction, a tape head switching switch for switching the magnetic head is provided, and the switch is switched according to recording or reproducing operation. Need to take control. The magnetic head coil is also used in the recording mode and the reproducing mode. For example, in the recording mode, one end is grounded and the recording signal is applied from the other end. In the reproduction mode, the other end of the magnetic head coil is grounded and the reproduction signal is obtained from the one end. In that case, especially the side grounded in the reproduction mode must be completely grounded. This is because the gain of the reproduction amplifier that amplifies the signal from the magnetic head coil is as high as about 60 dB, and if even a small amount of noise leaks from the recording amplifier side, the original reproduction signal will be greatly disturbed.

Such a recording / reproducing circuit is disclosed in JP-A-62-1.
No. 65490.

[0004]

As described above, a transistor switch is required for grounding in the reproduction mode. However, since an AC bias voltage of 100 V _PP is applied to the transistor at the time of recording, the above transistor is used. When the switch is integrated into an IC, the IC must be formed by a high breakdown voltage process. However, an element such as a transistor in an IC manufactured by a high breakdown voltage process is apt to generate noise, which is a problem.

[0005]

The present invention has been made in view of the above points, and a magnetic head coil for recording and reproducing a signal on a recording medium, and a recording amplifier connected to one end of the magnetic head coil. A reproduction amplifier connected to one end of the magnetic head coil, an oscillation bias circuit connected to the other end of the magnetic head coil, the oscillation bias circuit during recording, and the operation of the oscillation bias circuit during reproduction. And a control means for controlling the amplitude of the AC output signal of the oscillation bias circuit.

[0006]

According to the present invention, the amplitude of the AC output signal of the oscillation bias circuit is adjusted by the oscillation bias circuit itself and then output. Therefore, the amplitude is adjusted between the oscillation bias circuit and the magnetic head coil. No means is required, and both can be directly connected. Therefore, a transistor switch for grounding the other end of the magnetic head coil during reproduction is not required. Therefore, when the recording / reproducing switching circuit is integrated into an IC, it is not necessary to use a high breakdown voltage process, and noise can be reduced.

[0007]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
(1) is a magnetic head coil for recording / reproducing a signal on / from a recording medium, (2) is a recording amplifier connected to one end of the magnetic head coil (1), and (3) is the magnetic head coil (1). A reproducing amplifier connected to one end, (4) an oscillating bias circuit connected to the other end of the magnetic head coil (1), (5) operating the oscillating bias circuit (4) during recording, and A switch for stopping the operation of the oscillation bias circuit (4), (6) a control means for controlling the amplitude of the AC output signal of the oscillation bias circuit (4),
(7) is a switch that is closed during recording, and (8) is a switch that is closed during playback.

During recording, the switches (5) and (7) are closed and the switch (8) is opened. When the switch (5) is closed, the oscillation bias circuit (4) starts oscillating operation,
An AC output signal having an AC bias of about 0 to 80 KHz is generated in the primary coil (9). Therefore, a similar AC output signal is generated from the secondary coil (10) and flows to the output end of the recording amplifier (2) via the magnetic head coil (1). On the other hand, the recording signal from the terminal (11) is amplified by the recording amplifier (2) via the switch (7). The resistor (12) and the capacitor (13) form a resonance circuit together with the inductance of the magnetic head coil (1) and impart an equalizer characteristic to the recording signal. The impedance of the secondary coil (10) viewed from the magnetic head coil (1) is about 10 [Ω], and they are substantially connected.
Therefore, the recording signal can be supplied to the magnetic head coil (1).

During reproduction, the switches (5) and (7) are opened and the switch (8) is closed. When the switch (5) is opened, the oscillation bias circuit (4) stops the oscillation operation. Then, no AC signal is generated in the secondary coil (10), and the other end of the magnetic head coil (1) is grounded. Since the output impedance of the recording amplifier (2) is low, the reproduction signal current from the magnetic head coil (1) flows to the output end of the recording amplifier (2). The magnetic head coil (1), together with the resistor (12) and the capacitor (13), constitutes a resonance circuit that gives frequency characteristics again. Therefore, the reproduced signal with frequency characteristics is
It is amplified by the reproduction amplifier (3) via the capacitor (14) and the switch (8) and obtained at the output terminal (15).

Therefore, according to the circuit of FIG. 1, it is possible to record and reproduce signals without connecting switches to both ends of the magnetic head coil (1).

[0011]

As described above, according to the present invention, it is not necessary to connect a switch for recording / reproducing switching to the magnetic head coil, so that it is not necessary to integrate the recording / reproducing switching circuit into an IC by a high breakdown voltage process. , Noise can be reduced.

[Brief description of drawings]

FIG. 1 is a recording / reproducing switching circuit of the present invention.

[Explanation of symbols]

 (1) Magnetic head coil (2) Recording amplifier (3) Reproducing amplifier (4) Oscillation bias circuit (5) Switch

Claims (2)

[Claims] 1. A magnetic head coil for recording / reproducing a signal on / from a recording medium, a recording amplifier connected to one end of the magnetic head coil, a reproduction amplifier connected to one end of the magnetic head coil, and the magnetic recording medium. An oscillation bias circuit connected to the other end of the head coil, a switch that operates the oscillation bias circuit during recording and stops the operation of the oscillation bias circuit during reproduction, and controls the amplitude of the AC output signal of the oscillation bias circuit. And a control means for controlling the recording / reproducing switching circuit. 2. The oscillation bias circuit includes a primary coil for generating an AC signal, and a secondary coil for transmitting the AC signal from the primary coil, the secondary coil being the magnetic head coil. The recording / reproducing switching circuit according to claim 1, wherein the recording / reproducing switching circuit is connected to the other end.