JPH0329761Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to an integrated circuit for head switching used in a video tape recorder (hereinafter referred to as VTR) equipped with recording and playback functions.

(B) Prior art In general, in a VTR, when a video signal is recorded on a videotape by a video head during recording, and when the video signal recorded on the videotape is reproduced during playback, the video signal is amplified. Therefore, an integrated circuit (hereinafter referred to as an IC) is used which has a built-in recording amplifier and a playback head amplifier.

As shown in Figure 1, the configuration is such that an input terminal 2 is connected to one end of the video head 1, an output terminal 3 is connected to the other end, and a switch 4 for switching between recording and playback (usually called a recording/playback switch) is connected. A head amplifier 5, a preamplifier 6, and an amplifier 7 are connected in sequence to the input terminal 2, while a recording amplifier 8 is connected to the output terminal 3. When the changeover switch 4 is on the A side, it is set to the recording mode, and when it is on the B side , it is set to the playback mode. )
The recorded video signal is added to the video signal, adjusted to a predetermined amplitude, and reproduced on the screen of a television receiver.

However, in the above configuration, the common impedance of the ground line inside the IC and the IC are connected between the ground point _G1 of the video head 1 and the ground point _G2 of the head amplifier 5 provided inside the IC 9 during playback. A potential difference occurs due to the impedance of the ground line (on the copper foil pattern) on the printed circuit board, and this adversely affects the video input signal applied to the head amplifier 5, which has a very low level, resulting in deterioration of the signal-to-noise ratio (S/N) and distortion. Furthermore, since the voltage gain between the input and output of the head amplifier 5 is high, it has become a drawback of causing unstable operation such as oscillation.

(c) Purpose of the invention The purpose of the invention is to improve the S/N ratio during VTR playback by eliminating the above-mentioned drawbacks.

(d) Structure of the invention The invention comprises an input terminal connected to one end of a video head, an output terminal connected to the other end of the video head, a changeover switch for switching between recording and playback modes, and an input terminal connected to the other end of the video head. In a head switching integrated circuit comprising a head amplifier and a recording amplifier connected to a terminal and an output terminal, respectively, and a ground terminal, a first ground terminal to which a ground line of the changeover switch and a ground line of the head amplifier are grounded; , and a second ground terminal connected to a ground line of a recording amplifier, etc. other than the head amplifier, are provided on the integrated circuit.

(E) Example Figure 2 shows an example of the present invention, in which the same elements as in Figure 1 are given the same figure numbers, and 10 is IC 11.
12 is a control circuit for controlling the recording/playback switch 10;
13 is a first terminal connected to the ground line of the head amplifier 5 and the recording/playback switch 10; 14 is a second ground terminal connected to the ground lines of the recording amplifier 8, preamplifier 6, and amplifier 7;
15 is a control terminal connected to the control circuit 12.

Next, to explain the operation of the present invention, first, when a control signal for recording is generated by operating a recording operation button (not shown), the control terminal 15
The control signal is applied to the recording/playback switch 10, and the control circuit 12 sets the recording/playback switch 10 to position A in FIG. and recorded on a magnetic tape (not shown).

On the other hand, during playback, a control signal for playback is generated by operating the operation button, the control signal is applied to the control terminal 15, and the control circuit 12 moves the recording/playback switch 10 to position B in FIG. switching,
The video signal recorded on the magnetic tape is applied to a head amplifier 5, a preamplifier 6, and an amplifier 7,
The screen is played back on a display device such as a television receiver connected to the VTR.

During playback, various signals such as video signals, audio signals, and control signals appear on the printed circuit board on which the IC is mounted, and the ground line is waved, but the ground lines of the head amplifier 5 and the video head 1 are constructed in the same way. This ground line is commonly taken out at the first ground terminal 13, and the recording amplifier 8, preamp 6,
The ground lines connected to the amplifier 7 are connected separately through the second ground terminal 14, and potential fluctuations do not occur between the ground lines, allowing stable operation.

(f) Effects of the invention According to the head switching integrated circuit of the present invention, first, the head switching switch is provided in an integrated circuit (IC), and the grounding line of the head switching switch and the grounding line of the head amplifier are common. Since a ground line is provided for the recording amplifier, etc., in addition to this connection, it is possible to prevent a drop in S/N during playback in a VTR using a conventional head switching integrated circuit, and furthermore, There is no need to consider the voltage drop caused by the copper foil when designing the copper foil pattern of a printed circuit board using an integrated circuit, and there is an advantage that the design becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of a conventional integrated circuit for switching heads, and FIG. 2 is a block diagram of the main parts of the integrated circuit for switching heads according to the present invention. Explanation of main drawing numbers, 1...Video head, 2...
Input terminal, 3...Output terminal, 4,10 ...Recording/
Playback selector switch, 5...Head amplifier, 6...
Preamplifier, 7...amplifier, 8...recording amplifier,
9, 11 ...IC, 13...first ground terminal, 1
4...Second grounding terminal.

Claims (1)

[Scope of utility model registration request] an input terminal connected to one end of the video head;
an output terminal connected to the other end of the video head;
A playback terminal connected to the other end of the video head and a signal from the input terminal depending on the recording mode,
In a head switching integrated circuit comprising a changeover switch that selectively generates a signal at the terminal according to a playback mode, and a head amplifier and a recording amplifier connected to the input terminal and the output terminal, respectively, the output of the changeover switch is 1. An integrated circuit for head switching, characterized in that the terminal and the ground line of the head amplifier are directly connected in common and then grounded to the outside of the integrated circuit.