JPS5981984A - Video signal recording device - Google Patents

Abstract

PURPOSE:To increase the resolution of a video tape recorder by selecting a clamping circuit which suits to a carrier frequency selected by a control circuit through a switch circuit. CONSTITUTION:A video signal is inputted from an input terminal 1 and separated by an LPF2 into a luminance and a carrier chrominance signal and the separated luminance signal is inputted to the clamping circuit 3. Then, a control circuit 6 generates a control signal for switching a clamping voltage corresponding to the selected carrier frequency and this signal is inputted to the circuit 3. Thus, the clamping voltage of the circuit 3 is selected and the luminance signal is clamped by this clamping voltage. The luminance signal outputted from the circuit 3 is pre-emphasized and inputted to a clipping circuit 4. Further, the output of the control circuit 6 is inputted to the circuit 4 to clip the luminance signal by a selected clipping voltage and the resulting luminance signal is sent from the circuit 4 to an FM modulating circuit 5, whose output signal is recorded through a magnetic head 9.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an apparatus for recording video signals.

Conventional Example 1.1 Structure and Its Problems When recording a color video signal in a home video tape recorder (hereinafter referred to as VTR), the video signal is separated into a luminance signal and a carrier color signal, and the luminance signal is subjected to wave number modulation. However, the mainstream method is to frequency-convert the carrier color signal to a low frequency band, frequency-multiplex both signals, and record them on a magnetic recording medium.

FIG. 1(a) shows frequency allocation when recording a color video signal in the VH5 system. When the luminance signal to be recorded has a high frequency (8M) 4z or higher), the sideband spectrum of the frequency-modulated luminance signal and the sideband spectrum of the carrier color signal whose frequency has been converted to a low frequency are as shown in Figure 1. They overlap near IM and Hz on the frequency axis shown. As a result, during playback, high frequency luminance signals (8M++ or higher) appear as noise on the screen or are not transmitted, so the horizontal resolution remains at about 240 lines. On the other hand, with the development of television receivers incorporating comb-shaped filters and the increase in the resolution of household VTR cameras, it is desired that VTRs also have a high N resolution.

Furthermore, improvements in materials and advances in processing technology have been made in video heads, and similar advances have been made in video tapes, making it possible to record at shorter wavelengths. That is, it has become possible to record and reproduce data using a frequency allocation scheme as shown in FIG. 1 (03). .

OBJECTS OF THE INVENTION The present invention satisfies the demand for high-resolution recording by recording with the frequency allocation shown in Figure 1), and also addresses the conventional type shown in Figure 1 by switching the switch. The purpose of this invention is to propose a video signal recording device that can maintain compatibility with conventional types by enabling low-resolution recording.

In order to achieve the above object, the present invention includes a control circuit for selecting a carrier frequency of a frequency modulation circuit, and a first clamp circuit having a clamp voltage corresponding to a general transmission frequency. a second clamp circuit having a clamp voltage corresponding to another carrier wave frequency; and a switch circuit for switching these clamp circuits; It is configured so that the selection can be made via the .

Description of examples An embodiment of the present invention will be described below based on the drawings.

First, the principle of the present invention will be explained. FIG. 2 shows the characteristics of voltage/frequency conversion in the FM modulation circuit (FIG. 8 (5)). In FIG. 2, the voltage input to the FM modulation circuit (5) and the frequency output from the FM modulation circuit (5) change linearly. Therefore, the same FM modulation circuit (5
) can be achieved by increasing the DC component of the video signal input to the FM modulation circuit (5).

As shown in Figure 2, the input voltage required to output the conventional carrier wave sync chip frequency (8.4M) is V.
Let it be l. Since the input voltage and output frequency of the FM modulation circuit (5) are in a directly proportional relationship, when a voltage v2 larger than the input voltage ■ is input, the sync tip frequency of the carrier wave is increased to 4.
．． It is possible to set it to 4MHz.

FIG. 8 is a block diagram showing the basic configuration of the present invention. In FIG. 81, a video signal is input from an input terminal (1) and is separated into a luminance signal and a carrier color signal by a low-pass filter (2). The separated luminance signal is input to a clamp circuit (3).

Next, the control circuit (6) generates a control signal to switch the clamp voltage according to the selected carrier frequency,
This control signal is input to the clamp circuit (3). As a result, the clamp voltage of the clamp circuit (3) is selected and the luminance signal is clamped by the diffracted clamp voltage. Clamp circuit (3) The luminance signal outputted from the pre-emphasis circuit (not shown) is emphasized and input to the clip circuit #(4).

Further, the control circuit (6) generates a control signal for switching the clip voltage according to the selected clamp voltage, and inputs the control signal to the clip circuit (4). As a result, the clipping voltage of the clipping circuit (4) is selected, and the luminance signal is clipped with the selected clipping voltage. The luminance signal output from the clip circuit (4) is input to the FM modulation circuit (5).

Next, the output signal of the FM modulation circuit (5) is transferred to the recording amplifier circuit (
7) and the amplified output signal is sent to the rotating transformer (
8) Record on a magnetic tape (not shown) via a magnetic head (9).

Note that since a known configuration is used for recording the N fading signal, no particular description will be given here.

FIG. 4 is a circuit diagram showing a specific configuration of the clamp circuit (3). The luminance signal separated by the low-pass filter (2) is input to the input terminal a1 of the clamp circuit (3).

The luminance signal is transmitted through a coupling capacitor OQ and a resistor Uη0
An emitter follower circuit consisting of a transistor and an emitter follower circuit is input.

The luminance signal (+!) input to the input terminal 0[) of the clamp circuit (3) is simultaneously input to the horizontal synchronization signal circuit σ.The horizontal synchronization signal separation circuit O converts the horizontal synchronization signal from the luminance signal. (The transistor α is turned on during the section where the horizontal synchronizing signal is present, and the emitter follower circuit is turned on.)
Clamps the luminance signal output from.

Next, the control circuit (6) generates a control signal for switching the switch circuit Op in accordance with the selected carrier frequency. Here, the voltage of the DC power source 0 is assumed to be 1, and the voltage of the direct current source 0 [9] is assumed to be V2. When the control signal is connected to the DC power supply side, the clamp voltage is Vl, and when it is connected to the DC power supply oQ side, the clamp voltage is 2. The voltage to be clamped is selected as Vll or V2.The clamped luminance signal is sent to the clamp circuit (3) via an emitter follower circuit 1jlS (g) consisting of a transistor (2) and a resistor (a). Output to output terminal C console.

5N is a circuit 1'' showing a specific 413 configuration of the cleave circuit (4). The luminance signal -1J outputted to the output terminal (c) of the clamp circuit (3) is inputted to the pre-emphasis circuit 49. The pre-emphasis circuit) emphasizes the brightness and outputs it. The diode (b) clips the high level of the output luminance signal, and the diode 6υ clips the low level of the output luminance signal. Next, the control circuit (6) is clamped! I! , '+ The switch circuit (1) and the switch circuit - are switched according to the clamp voltages of (3) to select the voltage to be clipped. DC power source (to), DC power source - tri, voltage is 3, V4. (to the switch circuit)
When connected to the DC power supply (C) side, the clipped voltage of the diode (A) becomes v3, and when the switch circuit) is connected to the DC power supply (G) side, the clipped voltage of the diode (A) becomes v3. The voltage will be V4.

On the other hand, the voltage of DC power supply 1.3 and DC power supply ① is set to V5, immersion. When the switch circuit ■ is connected to the DC power source ( ) side, the voltage clipped by the diode 0◇ becomes v5, and when the switch circuit (b) is connected to the DC power source (2) side, the voltage clipped by the diode 0 υ The voltage applied will be v6.

The clipped video signal is output to the output terminal (b) of the clipping circuit (4) via an emitter follower circuit composed of a transistor (7) and a resistor (b).

As described above, the carrier wave frequency can be switched by selecting the clamp voltage of the video signal input to the FM modulation circuit using the linearity of the voltage-frequency conversion of the FM modulation circuit.

With the above-mentioned apparatus, it is possible to record with the frequency allocation shown in FIG. 1 (6). As a result, the sync chip frequency for one wave transmission is 4.4 MHz, so it is possible to transmit a wider IMI (z) band than before, and the horizontal resolution number is approximately 320. It is also possible to record with the conventional low frequency allocation as shown in Figure (4), and the conventional V'
Can maintain compatibility with IR.

Effects of the Invention According to the present invention, one clamp pressure can be selected with a simple configuration, recording can be performed by frequency modulating with different carrier frequencies, and high-resolution conversion of VTR can be achieved. Even conventional low frequency allocations can be stored, which is extremely advantageous industrially. .

[Brief explanation of drawings]

Figure 1 (G) (13) is a diagram showing frequency allocation during recording of a color video signal, Figure 2 is a voltage/frequency conversion characteristic diagram of the FM modulation circuit, and Figure 8 is a diagram showing the basic configuration of the present invention. FIG. 4 is a block diagram showing a specific configuration of the clamp circuit, and FIG. 5 is a diagram showing a specific configuration of the clip circuit. (3)...Clamp circuit, (4)...Clip circuit, (5)...FM modulation circuit, (6)...Control circuit,
αυ... Switch circuit, 0 → (g)... DC power supply agent Yoshihiro Morimoto Figure 1 Figure 2; 74

Claims (1)

[Claims] 1. When recording a color video signal on four magnetic recording bodies, the color video signal is divided into a luminance signal and a carrier color signal.
A device that frequency-modulates and records a luminance signal,
a control circuit that selects a carrier frequency of the frequency modulation circuit;
A first clamp circuit having a clamp voltage according to a certain carrier wave frequency, a second clamp circuit having a clamp voltage according to another carrier wave frequency, and a switch circuit for switching these clamp circuits; A video signal recording device in which a clamp circuit is selected via a switch circuit according to a carrier wave frequency selected by the circuit.