JPH0468883A - Fm recording device for video signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an FM recording device for video signals.

[Summary of the invention]

The present invention supplies an input video signal to an FM modulation circuit through a pre-emphasis circuit and a subsequent clip circuit, supplies an FM modulated video signal from the FM modulation circuit to a magnetic head, and records it on a magnetic tape. In an FM recording device for video signals, the difference signal between the input and output signals of the clip circuit is supplied to a low-pass filter, and the filtered output is
By providing a phase difference between the input and output signals of the clip circuit and adding a preshoot section to the portion where the level of the video signal supplied to the FM modulation circuit changes rapidly, This makes it possible to effectively prevent the reversal phenomenon and to improve waveform characteristics.

[Prior Art] In a VTR, in order to improve the S/N ratio of a reconstructed video signal, the video signal (luminance signal) is subjected to reenphasization, that is,
After emphasizing the high frequencies, FM modulation is performed, and the FM modulated video signal is recorded on a magnetic tape by a rotating magnetic head.

By the way, when a video signal is pre-emphasized, a portion where the level of the video signal suddenly changes from a low portion to a high portion becomes a white spot, causing an inversion phenomenon. Therefore, in order to avoid this, the spikes in the high level part of the pre-emphasized video signal are clipped and the FM
(Japanese Unexamined Patent Publication No. 59-208989@).

[Problem to be solved by the invention]

The present invention aims to propose an FM modulation recording device for video signals that can effectively prevent inversion phenomena and improve waveform characteristics.

[Means to solve the problem]

The present invention provides a pre-emphasis circuit (2) for manually inputting video signals.
and the FM modulation circuit (4) through the subsequent clip circuit (3), and the received F from the FM modulation circuit (4).
In an FM recording device for a video signal, which supplies an M modulated video signal to a magnetic node (6) and records it on a magnetic tape, a subtracter (8) obtains the difference between the input and output signals of the clip circuit (3). ), a low-pass filter (15) to which the subtracted output of the subtracter (8) is supplied and whose filtered output is supplied to the FM modulation circuit (4), and a clip circuit (3) supplied to the subtracter (8). and a phase shift circuit (7) that provides a phase difference between the input and output signals of the FM modulation circuit (4), and a preshoot section is added to a portion where the level of the video signal supplied to the FM modulation circuit (4) changes rapidly. It is something.

[Effect]

According to the present invention, the input video signal is supplied to the FM modulation circuit (4) through the pre-emphasis circuit (2) and the subsequent clip circuit (3), and the FM modulation circuit (4)
) is supplied to the magnetic head (6) to record the video signal on the magnetic tape.
In the recording device, the difference signal between the input and output signals of the clipping circuit (3) is supplied to the FM modulation circuit (4) through the low-pass filter (15), and is also supplied to the low-pass filter (15) by the phase shift circuit (7). A phase difference is given between the input and output signals of the crimp circuit (3) to be supplied.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG. A luminance signal and a carrier chrominance signal are separated from the color video signal, and the carrier chrominance signal is supplied to a frequency low-frequency conversion circuit, and the luminance signal is supplied from an input terminal (1) to a pre-emphasis circuit (2) for high-frequency conversion. After being emphasized, it is supplied to a clip circuit (3).

From the input signal of the crimp circuit (3), the clip circuit (3)
) The signal whose phase is advanced by the phase shift circuit (bypass filter) (7) of the output signal of the phase shift circuit (7) is
Subtraction is performed using a P-type transistor (8), and the subtraction output is passed through a low-pass filter (15) to an FM modulation circuit (4).
).

Although not shown, the FM modulated luminance signal from the FM modulation circuit (4) is added to the low frequency converted carrier color signal, and the added output is sent to the rotating magnetic head (one or 180°) through the amplifier (5). The information is supplied to a pair of angularly divided rotating magnetic heads (6) and recorded so as to form an inclined track on the magnetic tape.

In addition, pre-emphasis circuit (2), clip circuit (3)
, an FM modulation circuit (4) and an amplifier (5) are formed within the IC.

Next, the external circuit for the IC will be explained. The output signal of the clip circuit (3) is connected to the resistors (I3) and (14
) to the base of the PNP transistor (8) of the phase shifting circuit (7). The collector of the transistor (8) is grounded through a load resistor (12) and connected to the input side of the FM modulation circuit (4) through a low-pass filter (15). The input terminal of the clip circuit (3) is connected to the resistor (9
) to the emitter of the transistor (8). The emitter of the transistor (8) is connected to the resistor (10
) and a capacitor (11) in parallel circuit
connected to.

The capacitance of the capacitor (11) of the phase shift circuit (7) is selected to be approximately 27 pF, for example, so that the amount of phase advance of the signal is somewhat larger than the amount of phase lag of the signal in the clip circuit (3). .

A semi-fixed resistor (16) for frequency shift adjustment in the FM modulation circuit (4) is connected between the output side of the clip circuit (3) and the input side of the FM modulation circuit (4). A semi-fixed resistor (17) for adjusting the center carrier frequency in the FM modulation circuit (4) is connected between the input side of 4) and the constant voltage power supply +B reg.

Next, referring also to FIG. 2, the operation of the embodiment shown in FIG. 1 will be explained. When a brightness signal of an image that changes rapidly from black to white is supplied to the pre-emphasis circuit (2), a video signal a having white spikes as shown in FIG. 2A is obtained at its output side. When supplied to the clipping circuit (3), the white spike is clipped at a clip level lower than the conventional normal clip level and delayed in phase by a predetermined amount on the output side, as shown in FIG. 2B. A video signal can be obtained. In the phase shift circuit (7), the clear 1. After the output of the clipping circuit (3) is phase-advanced by a phase advance amount that is somewhat larger than the phase delay amount in the clip circuit (3), the phase-advanced video signal C (the 2C) is subtracted from the output a of the pre-emphasis circuit (2), and the subtracted output a-c obtained from the collector of the transistor (8) is supplied to the low-pass filter (15), whereby the second As shown in the figure, it becomes negative between the rising edge of the video signal C and the rising edge of the video signal a,
A positive signal d (D in FIG. 2) is obtained between the rising edge of the video signal a and the rising edge of the video signal S, and is added to the output video signal S of the clip circuit (3).

In this way, the positive part of the signal d in the second diagram makes it possible to effectively prevent the inversion phenomenon, and the negative part of the signal d adds a preshoot to the rising edge of the video signal. Good waveform characteristics are obtained.

Furthermore, on the playback side of the VTR, the subject F in the playback color video signal is
After the M-modulated luminance signal is FM demodulated, it is de-emphasized by a de-emphasis circuit.

[Effects of the Invention] According to the present invention described above, the input video signal is supplied to the FM modulation circuit through the pre-emphasis circuit and the subsequent clip circuit, and the FM modulated video signal from the FM modulation circuit is supplied to the magnetic head. In an FM recording device for video signals recorded on a magnetic tape, the difference signal between the input and output signals of the clipping circuit is supplied to a low-pass filter, the filtered output is supplied to the FM modulation circuit, and the input and output signals of the clipping circuit are By giving a phase difference between the signals and adding a preshoot section to the part where the level of the video signal supplied to the FM modulation circuit changes rapidly, it is possible to effectively prevent the reversal phenomenon and improve the waveform characteristics. It can be made good.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a timing chart for explaining the same. (2) is a pre-emphasis circuit, (3) is a clip circuit, (4) is an FM modulation circuit, and (6) is a rotating magnet. (7) is a phase shift circuit, (8) is a transistor, (1o
) is a resistor, (11) is a capacitor, and (15) is a low-pass filter.

Claims (1)

[Scope of Claims] An input video signal is supplied to an FM modulation circuit through a pre-emphasis circuit and a subsequent clip circuit, and an FM modulated video signal from the FM modulation circuit is supplied to a magnetic head and recorded on a magnetic tape. The FM recording device for video signals includes a subtracter that obtains the difference between the input and output signals of the clipping circuit, and a subtracted output of the subtracter is supplied, and the filtered output thereof is the filtered output of the FM video signal.
It has a low-pass filter supplied to the M modulation circuit, and a phase shift circuit that provides a phase difference between the input and output signals of the clip circuit supplied to the subtracter, An FM recording device for a video signal, characterized in that a preshoot section is added to a portion where the level changes rapidly.