JPH05325114A - Vtr recording circuit - Google Patents

Abstract

PURPOSE:To protect a video head against magnetization by blocking DC bias current of recording signal. CONSTITUTION:Recording signals from drive transistors Tr1-Tr3 and a DC bias voltage are applied on a rotary transformer T1. Switching transistors Tr6, Tr7, Tr10, Tr11 are provided with common emitters thus providing a bias power supply having voltage same as the emitter voltage of the drive transistors Tr1-Tr3. DC bias current is blocked by connecting the common emitters of the switch transistors Tr6, Tr7, Tr10, Tr11.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a VTR (Video Tape R).
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ecorder (magnetic recorder) recording circuit, and more particularly to a VTR recording circuit that blocks a DC bias current of a recording signal and eliminates the magnetization of a video head.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing a conventional VTR recording circuit, in which 11a is an SP (Standard Play) video head (L), 11b is an SP video head (R), and 12a is an EP (Extended Play). ) Video head (L), 12b EP video head (R), 13 rotary transformer,
Reference numeral 4 is a reproducing head amplifier IC. The recording signal passes through the drive circuit of the transistors Tr ₁ , Tr ₂ , Tr ₃ . In the case of standard mode recording, the recording signal is the switch transistor Tr ₄
Through the rotary transformer 13 and the transistor T
Connected to signal ground with r ₆ and Tr ₇ . The recording signal that has passed through the rotary transformer 13 is the SP video head 11
The data is recorded on the tape after flowing through a and 11b, but the switch transistor Tr ₈ is turned off so that no current flows on the triple head side.

In the case of the triple mode recording, the transistor Tr ₄ is off, the transistor Tr ₈ is on, passes through the rotary transformer 13, and is connected to the signal ground by the transistors Tr ₁₀ and Tr ₁₁ . The recording signal that has passed through the rotary transformer 13 flows through the EP video heads 12a and 12b and is recorded on the tape. Transistors Tr ₁ , Tr ₂ ,
A DC bias voltage is applied to the signal output from the drive circuit of Tr ₃ , and capacitors C ₁ and C ₂ are respectively placed on the SP video head side and the EP video head side in order to cut the direct current. The charge / discharge current in this case flows as shown by the arrow in the figure.

[0004]

As described above, in the conventional VTR recording circuit, the DC cut capacitor C is used when switching between the standard mode ← → triple mode recording at the rising of the DC bias voltage during recording and during recording. A large charging / discharging current flows in ₁ and C ₂ , and this current also flows in the video head side, so that the video head is magnetized, and the performance of the video head is seriously affected. To prevent this,
It is necessary to devise a method that does not allow a large current to flow through charging and discharging.

The present invention has been made in view of the above situation, and blocks a DC bias current of a recording signal without using a coupling electrolytic capacitor in a signal line connected to a rotary transformer, and It is an object of the present invention to provide a VTR recording circuit that prevents magnetization.

[0006]

To achieve the above object, the present invention provides a drive circuit for driving a recording signal, a rotary transformer to which a recording signal and a DC bias voltage are applied by the drive circuit, and the drive circuit. And a signal ground switch transistor to which the same voltage as the DC bias voltage is applied.

[0007]

A DC bias voltage is applied to the rotary transformer together with the recording signal from the drive circuit of the transistors Tr ₁ , Tr ₂ and Tr _{3 so} that the signal ground switch transistors Tr ₆ and Tr ₇ on the SP video head side and the EP video head side are connected. The emitters of the signal ground switch transistors Tr ₁₀ and Tr ₁₁ are made common, and the same bias power supply as the emitter voltage of the transistor Tr ₃ of the drive circuit is provided. By connecting the common emitter of the signal ground switch transistor _{Tr 6, Tr 7, Tr 10} , Tr 11, it is possible to prevent the DC bias current.

[0008]

Embodiments will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining an embodiment of a VTR recording circuit according to the present invention, in which 1a is an SP video head (L), 1b is an SP video head (R), and 2a is E.
P video heads (L), 2b the EP video heads (R), 3 is a rotary transformer, the reproducing head amplifier IC, drive transistor Tr ₁ to Tr ₃ is recording signal 4,
Tr ₄ is a switch transistor which is turned on in the standard recording mode, Tr ₆ and Tr ₇ are signal ground switch transistors which are turned on in the standard recording mode, Tr ₈ is a switch transistor which is turned on in the triple recording mode, and Tr ₁₀ and Tr ₁₁ are triple. Signal ground switch transistor that turns on in recording mode, Tr ₅ ,
Tr ₉ is a switch transistor which is turned on by reproduction, C ₁ and C ₂
Is a coupling capacitor for blocking the DC bias voltage applied to the recording signal, and C ₃ is a capacitor for flowing the recording signal from the common emitter to the ground.

The recording signal is applied to the base of the drive transistor Tr ₁ and becomes a low impedance signal in the drive circuit of Tr ₁ , Tr ₂ , Tr ₃ and the switch transistor Tr ₄ which is turned on in the standard recording mode and the triple recording mode. It is switched by the switch transistor Tr ₈ which is turned on. In the case of standard mode recording, only the signal current passes through the switch transistor Tr ₄ and the rotary transformer 3 together with the recording signal and the DC bias voltage, and only the signal current flows from the emitters of the signal ground switch transistors Tr ₆ and Tr ₇ to the coupling capacitor C ₃ and is grounded. However, since the same voltage as the DC bias voltage of the drive circuit is applied to the emitters of the signal ground switch transistors Tr ₆ and Tr ₇ , the DC bias current does not flow.

Further, in the case of the triple mode recording, only the signal current passes through the switch transistor Tr ₈ and the rotary transformer 3 together with the recording signal and the DC bias voltage from the emitters of the signal earth switch transistors Tr ₁₀ and Tr ₁₁ to the coupling capacitor. Although it flows through C ₃ to the ground, the DC bias current does not flow because the same voltage as the DC bias voltage of the drive circuit is applied to the emitters of the signal ground switch transistors Tr ₁₀ and Tr ₁₁ .

Since a bias voltage is always applied to the emitters of the signal ground switch transistors Tr ₆ and Tr ₇ on the SP video head side and the signal ground switch transistors Tr ₁₀ and Tr ₁₁ on the EP video head side, a recording signal bias is applied. No charge / discharge current is generated when switching between the presence / absence and the standard mode or triple mode during recording.

The reproducing system operates in the same manner as the conventional circuit. First, the reproduction signal magnetically converted by the SP / EP video head passes through the rotary transformer 3 and is guided to the reproduction head amplifier IC to amplify the reproduction signal. In that case,
Contrary to the recording, the switch transistors Tr ₅ and Tr ₉ are turned on, and the signal ground switch transistors Tr ₆ , Tr ₇ and Tr are turned on.
₁₀ and Tr ₁₁ are off.

As described above, in the conventional VTR recording circuit, the coupling electrolytic capacitor is used in order to prevent the DC bias current at the time of recording. At the time of switching, the charging / discharging current of the coupling electrolytic capacitor flows, and the video head is magnetized by this current. In order to prevent this, a common earth voltage is provided for recording, so that the coupling electrolytic capacitor becomes unnecessary and the video head is no longer magnetized.

[0014]

Since the present invention is constructed as described above, it has the following effects. That is,
By applying a bias voltage to the emitter of the signal ground switch transistor, it is possible to operate the circuit from the drive circuit of the recording signal between the rotary transformer and the signal ground switch transistor without using a charging / discharging element such as a capacitor. Since the magnetization of the video head due to charging / discharging can be prevented, the performance deterioration of the video head can be eliminated.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a VTR recording circuit according to the present invention.

FIG. 2 is a diagram showing a conventional VTR recording circuit.

[Explanation of symbols]

1a ... SP video head (L), 1b ... SP video head (R), 2a ... EP video head (L), 2b ... EP
Video head (R), 3 ... rotary transformer, 4 ... playback head amplifier IC.

Claims (1)

[Claims] 1. A drive circuit for driving a recording signal, a rotary transformer to which the recording signal by the driving circuit and a DC bias voltage are applied, and a signal ground switch transistor to which the same voltage as the DC bias voltage of the drive circuit is applied. VTR characterized by consisting of
Recording circuit.