JP3454652B2 - Color signal generation circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal generating circuit for an on-screen display used in a home VTR or the like, and more particularly to a color signal generating circuit for coloring an internally created screen.

[0002]

2. Description of the Related Art As a color signal generating circuit used for an internally created screen, one shown in FIG. 2 is known. In FIG. 2, reference numeral 4 is an 8-color 45-degree phase color signal generation circuit, and 1 is 4 times the subcarrier 4fsc (fsc is 3.58MHZ in the case of NTSC) corresponding to 4 times the frequency of the color burst signal. A frequency divider for dividing, 2 is a shift circuit, and a divider (1) is provided with flip-flops 1a and 1b, and a subcarrier 4 of 4 times
Divide fsc. The shift circuit (2) phase-shifts the output signal of the frequency divider (1) by a clock supplied via an inverter (3).

Various phase signals are generated by the functions of the frequency divider (1) and the shift circuit (2). That is, Phi 0 to Phi 7 shown in FIG. These eight signals are applied to the delay circuits (11) to (16). Each delay circuit performs a necessary delay so as to obtain a desired color and adjusts the phase. FIG. 3B shows a signal waveform after the delay.

As described above, according to the circuit of FIG. 2, a color signal having a phase angle of every 45 degrees obtained by dividing a signal of 4 fsc is created, and the color signal is delayed so as to have a desired color. Therefore, a color signal can be created.

[0005]

However, the color signal generation circuit of FIG. 2 has a problem that a dedicated delay circuit is required for each color. The delay circuit often requires a capacitor, etc., and is not suitable for use as an IC.
It also increases costs.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and divides a reference signal having a frequency four times as high as that of a color burst signal to generate a plurality of color signals having different phases by 45 degrees. A frequency divider for generating, a first delay circuit for delaying the phase of the reference signal, and a first output signal of the frequency divider for synchronizing with the delay signal of the first delay circuit and outputting as a burst signal. One cutout circuit is provided, and a plurality of color signals are obtained from the frequency divider.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a color signal generating circuit of the present invention, in which (1) divides a subcarrier 4fsc having a frequency four times as high as that of a color burst signal, and phases are different by 45 degrees. A frequency divider for generating a plurality of color signals, (2) is the above 4
a first delay circuit that delays the phase of the fsc signal by 15 degrees,
(3) is the second that delays the phase of the 4 fsc signal by 28 degrees
A delay circuit, (4) a first clipping circuit for synchronizing a first output signal of the frequency divider (1) with a delay signal of the first delay circuit (2) and outputting it as a burst signal, and (5) A second clipping circuit for synchronizing the second output signal of the frequency divider (1) with the delay signal of the second delay circuit (3) and outputting it as a color signal (yellow), (6) the frequency divider It is a third clipping circuit that synchronizes the third output signal of (1) with the delay signal of the second delay circuit (3) and outputs it as a color signal (blue).

Since the frequency divider (1) is composed of the same circuit as that shown in FIG. 2, its explanation is omitted. The cutout circuit is composed of a D-type flip-flop, and the output signal of the frequency divider (1) is D
The output signal of the delay circuit is applied to the terminal at the clock terminal. The phase relationship of the color signals is shown in FIG. In FIG. 4, the burst signal exists at a position of 180 degrees on the BY axis. In FIG. 4, 0 degrees, 45 degrees, 90 degrees, 13
5 degrees, 180 degrees, 225 degrees, 270 degrees, and 315 degrees can be created by the frequency divider (1) in FIG. In FIG. 4, focusing on green and magenta, green is 2
It is located 25 to 16 degrees ahead, and magenta is 4
It is located 5 to 16 degrees ahead. Therefore, both can be adjusted by the same phase shift circuit.

Further, in FIG. 4, focusing on red and cyan, red is located 90 ° to 14 ° ahead, and cyan is also located 270 ° to 14 ° ahead. Therefore, both can be adjusted by the same phase shift circuit. Green and magenta should be advanced 16 degrees, and red and cyan should be advanced 14 degrees. Both are very close together.

Therefore, in the present invention, the amount of phase shift is made the same by advancing by 15 degrees for all four colors to unify them. 1
If it is 5 degrees, all four colors are offset by 1 degree, and the original color is hardly damaged. A phase shift circuit may be used to shift the phase by 15 degrees, but the phase of the burst signal is delayed by 15 degrees. Thereby, four colors can be created relatively. The color signal is displayed with a phase difference with respect to the burst signal.

The situation is shown in FIG. Terminal (7) in Figure 1
Is applied with a signal of 4 fsc. The 4fsc signal is delayed by 15 degrees in the first delay circuit (2) and applied as a clock signal to the first cutout circuit (4) that generates a burst signal. From the frequency divider (1), Q1 to Q6 whose phases differ by 45 degrees are generated. This is shown in FIG. 4fsc in FIG. 5 represents the signal of 4fsc from the terminal (7).
When the signal of fsc is divided into 1/4, Q1 to Q6 of frequency fsc are obtained. The signal Q1 is applied as a data signal to the first cutout circuit (4). Therefore, the burst signal shown by Q1a in FIG. 5 is obtained from the first clipping circuit (4). A frequency divider (1) is provided by the phase shift of this burst signal.
The divided output from will show the following colors:

Q2 = red 105 degrees Q3 = magenta 60 degrees Q5 = cyan 285 degrees Q6 = green 240 degrees As a result, the remaining two colors are yellow and blue, and it suffices if they can be displayed. In FIG. 4, yellow is
It is 13 degrees behind the burst signal, and Blue is 13 degrees behind the 0 degree signal. Therefore, both of them can adjust the phase by a common means. First delay circuit (2)
Is delayed by 15 degrees, so yellow is 15 degrees +
It suffices that a total of 28 degrees is delayed by 13 degrees. Therefore,
The second delay circuit (3) delays 28 degrees. The signal delayed by 28 degrees is shown in FIG.
Shown as Y. The signal Q1b (yellow) is obtained by cutting out the signal Q1 in the second cutting circuit (5) using the 28-degree DELAY as a clock.

At the same time, the signal Q4a (blue) is obtained by cutting out the signal Q4 by the third cutting circuit (6) using 28 degrees DELAY as a clock. Therefore, according to the circuit of FIG. 1, 6 colors can be generated by using only two delay circuits.

[0014]

As described above, according to the present invention, it is possible to provide a color signal generating circuit capable of displaying 6 colors by using only two delay circuits and using the rest of the logic circuits. Therefore, the number of delay circuits can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a color signal generation circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional color signal generation circuit.

FIG. 3 is a waveform chart for explaining FIG.

FIG. 4 is a phase vector diagram for use in explaining FIG.

FIG. 5 is a waveform diagram for explaining FIG.

[Explanation of symbols]

(1) Frequency divider (2) First delay circuit (3) Second delay circuit (4) First cutting circuit (5) Second cutting circuit (6) Third cutting circuit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 9/44-9/78

Claims (3)

(57) [Claims] 1. A frequency divider that divides a reference signal having a frequency four times that of a color burst signal to generate a plurality of color signals that differ in phase by 45 degrees, and a first delay that delays the phase of the reference signal. A circuit and a first clipping circuit for synchronizing the first output signal of the frequency divider with the delay signal of the first delay circuit and outputting it as a burst signal, and obtaining a plurality of color signals from the frequency divider. A color signal generation circuit characterized by the above. 2. The color signal generating circuit according to claim 1, wherein the frequency divider generates a color signal including at least one of green, cyan, magenta, and red. 3. The color signal generating circuit according to claim 1, wherein the delay amount of the first delay circuit is around 15 degrees.