JPH0721012Y2 - Sub-screen forming circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an improvement of a dual type child screen signal forming circuit.

(B) Conventional technology The so-called picture-in-picture function of inserting a sub-screen into a main screen has been adopted in various video tape recorders, for example, SECAM color signals and PAL.
A dual screen sub-screen forming circuit is also used in a video tape recorder that records and reproduces color signals.

FIG. 2 shows a circuit block diagram of this dual type child screen forming circuit. As is clear from this figure, the sub-screen forming circuit consists of the SECAM signal processing circuit SE and the PAL signal processing circuit PA.
And a small screen signal generation circuit CH.

The SECAM signal processing circuit SE separates the luminance signal from the first low-pass filter 1 and the modulated color signal from the first band-pass filter 2 when the SECAM color video signal as the parent signal is input. This modulated color signal is band-limited by the bell filter 3 and input to the first SECAM decoder 4, where it is demodulated and a synchronized color difference signal is derived. Further, this color difference signal is derived through the second low pass filter 5.

These luminance signal and color difference signal are respectively input to the first switch S1 and the second switch S2 as parent screen information. The first switch S1 selects the luminance signal of the small screen signal only at the fitting portion of the small screen, and the second switch S2 selects the color difference signal of the small screen signal only at the fitting portion of the small screen. Select. The luminance signal of the first switching output is 80
The color difference signal of the second switching output is input to the 0 nsec delay circuit 6 and is converted again by the SECAM encoder 7 into a modulated color signal in line order. This modulated color signal is input to the inverse bell filter 9 and is added to the delayed output by the adder circuit 8 to be derived as a SECAM color video signal in which the child screen is inserted in the parent screen.

Further, in the PAL signal processing circuit PA, the color difference signal of the small screen signal is input to the PAL encoder 25 to form a modulated color signal, which is added to the luminance signal of the small screen signal by the adding circuit 24 for the small screen. The PAL color video signal is formed and is input to the sixth switch S6 together with the PAL color video signal which is the parent signal to form the PAL color video signal in which the child screen is inserted in the parent screen.

Further, in the small screen signal generation circuit CH, the small screen signal is the third
The low-pass filter 10 separates the luminance signal, and the second band-pass filter 11 separates the PAL modulated color signal into the third signal.
The bandpass filter 12 separates the SECAM modulated color signal. The second band pass output is demodulated by the PAL decoder 13 and converted into a color difference signal. The third bandpass output is SECA after band-limited by the second bell filter 14.
The data is input to the M decoder 15, demodulated, and simultaneously converted into a color difference signal. The fifth switch S5 selects the color difference signal according to the color signal input as the sub-screen signal and inputs the output to the fourth low pass filter 16. The luminance signal and the color difference signal of the child screen signal derived as a result are input to the field memory 17.

The field memory 17 performs writing and reading according to the memory control circuit 20, and the memory control circuit writes the sync signal obtained by inputting the sub-screen signal to the first horizontal and vertical sync separation circuit 18 at the time of writing. Input to the write control means to form a write address, and at the time of reading, a sync signal obtained by inputting the main screen signal to the second horizontal and vertical sync separation circuit 19 is input to the read control means to form a read address. The memory access control means appropriately generates write and read address signals. The clock generated by the clock generation circuit 21 is used for forming an address signal.

The luminance signal and the color difference signal, which are generated from the field memory 17 in synchronization with the parent screen signal and constitute the child screen signal, have their high frequency components cut by the fifth low pass filter 22 and the sixth low pass filter 23, respectively. Is derived as

In the above-described conventional configuration, the SECAM signal processing circuit SE switches the color difference signals because when the line-sequential FM color signals are switched, the modulated color signals cause phase discontinuity at the switching timing and are decoded color difference signals. The PAL signal processing circuit PA can directly switch the modulation color signal because the PAL encoder 25 forms a modulation color signal in phase with the color signal phase of the parent screen signal. .

The seventh switch S7 selects an output signal according to the color signal system of the parent screen signal.

(C) Problems to be solved by the invention However, in the above-described conventional technique, the position of the displayed sub-screen is different depending on whether the main screen signal is the SECAM color video signal or the PAL color video signal. There was a difference. That is, in the case of SECAM, the child screen is to the left, and in the case of PAL, it is to the right.

The reason is that the parent screen signal is delayed by the first LPF only in the case of SECAM even though the child screen signal is generated in synchronization with the sync signal of the parent screen signal. In the case of the conventional example described above, the delay amount is 600 nsec, which is offset by about 0.9% of the screen.

Therefore, in the present invention, when the main screen is the SECAM color video signal, the generation of the sub-screen signal is delayed by the delay period of the first LPF.

(D) Means for Solving the Problems The present invention, in the above-described conventional configuration, delays the generation of the child screen signal only when the parent screen signal is the SECAM color video signal in the child screen signal generation circuit. It is characterized in that a delay means is provided.

(E) Operation Therefore, according to the present invention, the small screen signal is displayed at a predetermined fixed position regardless of the color signal system.

(F) Embodiment Hereinafter, the present invention will be described according to an embodiment shown in FIG.

The present embodiment shown in FIG. 1 adopts the present invention to the conventional circuit shown in FIG. 2, and the same components as those of the prior art are designated by the same numbers as in FIG. Omit.

The feature of the present embodiment is that the generation of the sub-picture signal is delayed by 600 nsec in consideration of the delay amount of 600 nsec generated in the SECAM processing circuit SE for Y / C separation.

Therefore, in this embodiment, the parent screen horizontal sync signal output of the second sync separation circuit 19 is input to the delay means 26 to output the sync signal of 600 nse.
Only when the SECAM color video signal is input as the main screen signal due to the delay c, the delay synchronizing signal is input to the read control means by the eighth switch. Therefore, the derived sub-picture signal is derived with a delay of 600 nsec, and the SECAM signal processing circuit SE matches the timing with the color difference signal.

In this embodiment, no delay means is used for outputting the parent screen vertical sync signal of the second sync separation circuit 19, because the vertical offset of the screen is as small as 0.003%.

Further, although the read timing of the field memory 17 is delayed in the present embodiment, it goes without saying that the present invention also includes a configuration in which the read signal may be delayed.

(G) According to the present invention, according to the present invention, the display position of the sub-screen is constant regardless of the color system of the main screen signal, and the sub-screen is not displaced by switching the system, and the effect is great. Is.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a circuit block diagram of a conventional circuit. SE …… SECAM signal processing circuit PA …… PAL signal processing circuit CH …… Slave screen signal generation circuit 26 …… Delay means

Claims (1)

[Scope of utility model registration request] 1. A SECAM signal processing circuit for decoding an SECAM color video signal input as a parent signal and performing an encoding process after inserting a child screen baseband color signal, and a PAL color video signal input as a parent signal. A PAL signal processing circuit for inserting a PAL-encoded child screen baseband color signal into the PAL signal processing circuit, and a child screen signal generation circuit for forming and deriving a child screen baseband color signal in synchronization with the parent signal. In a dual type child screen forming circuit, delay means for delaying the generation of the child screen signal to the SECAM signal processing circuit is provided in the child screen signal forming circuit. .