JP2564987B2 - Video signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a home video magnetic recording / reproducing apparatus (hereinafter referred to as home VT).
R) and the like, and more particularly to a signal processing circuit that has improved reproducibility during reproduction of a luminance signal that has been subjected to emphasis processing during recording.

[Conventional technology]

The video signal processing of the conventional home VTR has a configuration as shown in FIG. 4, for example. In the figure, at the time of recording, a video signal to be recorded is subjected to predetermined processing by a recording processing circuit 17 and then written on a magnetic tape 21 via a selector 19 (selecting the “R” side) and a magnetic head 20. On the other hand, at the time of reproduction, the signal read by the magnetic head 20 from the magnetic tape 21 is input to the reproduction processing circuit 18 via the selector 19 (selecting the "P" side). The signal input to the reproduction processing circuit 18 is restored to a video signal by a predetermined process and output as a reproduction video signal. In the recording system processing circuit 17, for example, as processing of the video luminance signal, AGC processing, emphasis processing,
White / dark clip processing, FM modulation processing, etc. are performed, and in the reproduction processing circuit 18, FM demodulation processing, de-emphasis processing, noise removal processing, luminance signal / color signal synthesis processing, etc. are performed.

Here, in the emphasis process at the time of recording, since the noise superimposed on FM in the subsequent process has frequency dependence, that is, the noise component increases as the frequency becomes higher, the signal-to-noise ratio at the time of reproduction, that is, S / This is done to improve the N ratio. Specifically, the high frequency component of the video luminance signal to be recorded before FM modulation is emphasized. On the other hand, after FM demodulation during playback, high-frequency components are suppressed by de-emphasis processing, which has the inverse characteristics of this emphasis processing circuit, and noise components in the high-frequency region are suppressed by returning to the original video luminance signal. To do.

FIG. 5 is a block diagram of a configuration example of a conventional reproduction system processing circuit. In the figure, the FM signal recorded on the magnetic tape is input to the FM demodulation circuit 2 via the limiter circuit 1 to restore the video signal. The output video signal from the FM demodulation circuit 2 is input to the main de-emphasis circuit 4 and the non-linear de-emphasis processing 5 after the FM carrier signal component is removed by the low pass filter 3, and the high frequency component is emphasized by the emphasis processing in advance during recording. A high-frequency component suppression process is performed on the generated video signal so as to have a characteristic opposite to the emphasis process, and the resulting signal is output to the reproduction signal processing circuit 12 in the subsequent stage.

FIG. 6 is a waveform diagram showing the operations of the conventional emphasis processing and reproducing system processing circuit de-emphasis processing at the time of recording shown in FIG. FIG. 6 (a) shows a video luminance signal at the time of recording, and FIG. 6 (b) shows a video luminance signal subjected to the emphasis processing before the recording FM modulation processing. At the time of recording, the FM modulation process is further performed, and the FM signal recorded on the magnetic tape is demodulated by the limiter circuit 1, the FM demodulation circuit 2 and the low-pass filter 3 and subjected to the emphasis process shown in FIG. 6 (b). Image brightness signal is obtained and further main de-emphasis processing 4,
The original video luminance signal is restored by the non-lin adi emphasis processing 5.

[Problems to be Solved by the Invention]

In the video signal processing circuit of this conventional example, the main de-emphasis circuit 4 and the non-linear de-emphasis circuit 5 that perform de-emphasis processing are provided with the characteristic opposite to that at the time of the emphasis processing at the time of recording.
As shown in FIG. 6 (c), it is intended to reproduce the same signal as the recorded video luminance signal with respect to the recorded video luminance signal of FIG. Due to the influence of the non-linear circuit such as the white / dark clip processing in FIG. 6 or the phase delay by the low-pass filter 3, the video luminance signal as shown in FIG. There is a drawback that the reproducibility for the components is impaired.

It is an object of the present invention to provide a video signal processing circuit that eliminates such drawbacks and improves reproducibility for high frequency components such as edge components.

[Means for solving the problem]

The configuration of the present invention, FM demodulation means for demodulating the video signal FM-modulated after subjected to the emphasis processing in advance,
In a video signal processing circuit having a low-pass filter for removing an FM carrier component from an output signal from the FM demodulation means and a de-emphasis processing means, the output of the low-pass filter is phase-shifted and supplied to the de-emphasis processing means. A phase shift circuit, a first high-pass filter that inputs the output of the phase shift circuit and passes the high-frequency component thereof, a limiter circuit that controls the amplitude of the output of the first high-pass filter, and an output of the limiter circuit. A subtractor connected to the subtraction input, a second high pass filter connecting the output of the de-emphasis processing means to the subtraction input of the subtractor through the high frequency component of the output, and the output of the subtractor are input to output the output. A control circuit connected to the control input of the phase shift circuit as a phase shift control signal, and a video output signal from the output end of the de-emphasis processing means. It is characterized by outputting.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a video luminance signal reproducing system circuit according to an embodiment of the present invention, and those having the same function in FIG. 5 are designated by the same reference numerals. In this embodiment, the output of the low pass filter 3 is connected to the phase shift circuit 10, and the output of the phase shift circuit 10 is connected to the input of the high pass filter 6 and the input of the main de-emphasis circuit 4. The output of the high-pass filter 6 is connected to the subtracted input of the subtractor 9 via the limiter circuit 7, and the output of the non-linear de-emphasis circuit 5 is
It is connected to the input of the high-pass filter 8 and the reproduction signal processing circuit 12, and the output of the high-pass filter 8 is a subtractor 9.
Of the control circuit 11 connected to the subtraction input of
The output of the control circuit 11 is connected to the control input of the phase shift circuit 10.

2 (a) to (g) are waveform diagrams for explaining the circuit operation of FIG. A video luminance signal as shown in FIG. 2 (a) is input to the recording system signal processing at the time of recording, and FIG.
After being subjected to the emphasis process as shown in, it is FM-modulated and recorded on the magnetic tape. In this case, the limiter circuit 1, FM demodulation circuit 2 and low-pass filter 3 are used during playback.
After FM demodulation, it is input to the phase shift circuit 10. Here, when the phase shift circuit 10 gives an output to the main de-emphasis circuit 4 in the subsequent stage without performing any processing on the output of the low-pass filter 3, the main de-emphasis circuit 4 and the non-linear de-emphasis circuit 5 Fig. 2 (c)
The output indicated by is output to the output point of the non-linear de-emphasis circuit 5. Here, the video luminance signal that has been FM demodulated and not subjected to de-emphasis processing is input to the high-pass filter 6 from the output of the phase shift circuit 10 to remove the DC component, and then the limiter circuit 7 sets a predetermined V _L1 , V
_The amplitude is limited at the level _L2 (Fig. 2 (d)). Further, the output of the non-linear de-emphasis circuit 5 is input to the high pass filter 8 to remove the DC component (Fig. 2 (e)). The respective outputs of the limiter circuit 7 and the high-pass filter 8 are obtained by the subtractor 9 as a difference output as shown in FIG. Here the control circuit 11
Uses the output of the subtractor 9 as a control input and gives the operating point of the phase shift amount control to the phase shift circuit 10. This time,
The control circuit 11 may output a control output for correcting the phase shift amount of the phase shift circuit 10 so that the difference output of the subtractor 9 becomes 0, for example.

By doing so, as shown in FIG. 2 (g), the output of the non-linear de-emphasis circuit 5 (FIG. 6 (c)) in which the waveform reproducibility was impaired in the conventional example,
Correction is applied and a good video luminance signal can be restored.

FIG. 3 is a block diagram of a second embodiment of the present invention.
The phase shift circuit 10 in FIG. 1 comprises a gyrator 13 and a control circuit 11 comprising an amplifier 14 and a smoothing circuit 15. That is, the difference output of the subtractor 9 is amplified by the amplifier 14 by a predetermined amount and then smoothed by the smoothing circuit 15 to obtain a control voltage for the phase shift control of the phase shift circuit constituted by the gyrator 13.

According to this embodiment, since the gyrator 13, the amplifier 14, and the smoothing circuit 15 can be formed on a semiconductor integrated circuit (hereinafter referred to as an IC), for example, functions such as a main de-emphasis circuit and a non-linear de-emphasis circuit which are conventionally integrated into an IC are provided. Can be realized on the same IC.

〔The invention's effect〕

As described above, according to the present invention, the high-frequency components before and after the de-emphasis process are extracted, and the difference output thereof is used as the control input to perform the phase shift correction on the signal before the de-emphasis process, thereby performing the nonlinear correction. It is possible to cancel the influence of the phase shift delay due to the circuit and the low-pass filter and reproduce a good video luminance signal, and it is suitable for home VTRs and the like that require high image quality.

[Brief description of drawings]

1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a) to (g) are signal waveform diagrams showing the operation of FIG. 1, and FIG.
FIG. 4 is a block diagram showing a second embodiment of the present invention, FIG. 4 is a block diagram showing video signal processing of a general home VTR, and FIG. 5 is a block diagram showing an example of a conventional signal processing circuit. Sixth
5A to 5D are signal waveform diagrams showing the operation of FIG. 1,7 ... Limiter circuit, 2 ... FM demodulation circuit, 3 ... Low pass filter, 4 ... Main de-emphasis circuit, 5
…… Non-linear de-emphasis circuit, 6,8 …… High-pass filter, 9 …… Subtractor, 10 …… Phase shift circuit, 11 …… Control circuit, 12 …… Reproduction signal processing circuit, 13 …… Gyrator, 14 …… Amplifier, 15 ... Smoothing circuit, 17 ... Recording system processing circuit, 18 ... Reproduction system processing circuit, 19 ... Selector, 20 ...
Magnetic head, 21 ... Magnetic tape.

Claims (1)

(57) [Claims] 1. An FM demodulation means for demodulating an FM-modulated video signal after being subjected to emphasis processing in advance, a low-pass filter and a de-emphasis processing means for removing an FM carrier component from an output signal from the FM demodulation means. A video signal processing circuit comprising: a phase shift circuit for phase shifting the output of the low-pass filter and supplying it to the de-emphasis processing means; and a first phase for inputting the output of the phase shift circuit and passing its high-frequency component therethrough. A high-pass filter, a limiter circuit that controls the amplitude of the output of the first high-pass filter, and a subtractor that connects the output of the limiter circuit to the subtracted input,
A second high-pass filter that connects the output of the de-emphasis processing means through a high-frequency component and connects the output to the subtraction input of the subtractor; and the phase shift circuit that receives the output of the subtractor and uses the output as a phase shift control signal. And a control circuit connected to the control input of the video signal processing circuit, wherein a video output signal is output from the output terminal of the de-emphasis processing means.