JPH0473840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a video signal processing circuit, particularly to a burst signal phase shifter or hue adjuster.

[Technical background of the invention]

Generally, additional processing is sometimes performed on video signals, and in particular, one example of processing and operations that are added only to color signals is adjustment of color density and hue. Among these, for hue adjustment, only the color burst signal included in the original input video signal is extracted,
The phase is varied to replace the color burst signal of the original input video signal and serve as the reference phase for color reproduction,
Some result in a change in the hue of the original input video signal. The means for varying the phase of the color burst signal of the video signal will be described below with reference to the drawings. FIG. 3 shows a block diagram for varying the phase of a color burst signal extracted from a video signal.
1 and 2 are a phase shifter and a phase shifter with a function of varying the phase, and 3 is a fixed terminal, one of which is the output of the phase shifter, and the other one is a volume that is connected to the output of the phase shifter. 4 is a limiter that limits the amplitude of the signal voltage.

Next, the operation will be explained. In general, the amount of phase adjustment is determined with a maximum of ±45°, the amount of phase shift of the phase shifter is ±45°, the amount of phase shift of the phase shifter is -90°, and the output of the phase shifter is If the output of the phase shifter is e6, and the output of the volume 3 that combines e5 and e6 is e7, then the relationship shown in the vector diagram shown in Figure 4 is obtained, and the variable terminal of the volume 3 with respect to the original input video signal is The output constitutes a color burst signal phase shifter that can change the phase within a range of ±45°. The output from the variable terminal of the volume controller 3 is output by a limiter 4 at the subsequent stage to become a color burst signal with a constant amplitude.

[Problems with background technology]

The above phase shifter is usually constructed using an inductance, a capacitor, a delay line, etc., and depending on manufacturing errors, aging changes, temperature dependence, etc. of the inductance element, as well as errors and temperature dependence of the capacitor element, the desired It was difficult to obtain a phase shift amount of 1, and it was not possible to obtain characteristics with sufficient accuracy. In addition, regarding delay characteristics, it is difficult to manage delay time, and changes over time and temperature dependence are more adversely affected than inductance elements and capacitor elements. Therefore, there are two phase shifters like this.
Due to its characteristics, it was difficult to keep it within a predetermined range. Normally, a middle point click is provided on the volume 3 to specify a phase shift of 0°, which makes the phase of the color burst signal the same as that of the burst signal of the original input video signal. The change in the phase shifter will directly result in a phase error at the midpoint click, and even if one of the phase shifters is finely adjusted and the phase shift is set to 0° at the midpoint click, the phase error will occur due to changes over time and temperature. The drawback was that errors occurred.

[Purpose of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and uses a combination of a single-stage phase shifter and an inverting amplifier to adjust the angle of 90 degrees with respect to the color burst signal of the original input video signal. By creating a color burst signal with a phase difference of ±45° and adding it to the color burst signal of the original input video signal to an adder circuit, it is possible to obtain a color burst signal with a variable phase difference of ±45°. It is an object of the present invention to provide a hue adjuster having a simple configuration with few elements.

[Summary of the invention]

An original color burst signal synchronized with the color burst signal of the input video signal and a color burst signal whose phase is 90° different from the original color burst signal whose amplitude can be adjusted using a one-stage phase shifter, an inverting amplifier, and a volume control are added to an adder circuit. Provides a hue adjuster obtained by adding.

[Embodiments of the invention]

An embodiment of the present invention will be described below based on the drawings. In Figure 1, 11 is for the input signal.
A phase shifter that obtains an output with a phase difference of 90 degrees, 12 an inverting amplifier that obtains a phase difference of 180 degrees with respect to the input signal, 13
1 is a volume that combines the outputs of the phase shifter and the inverting amplifier, 14 is an adder circuit, and 15 is a limiter that keeps the amplitude constant.

Next, the operation of the present invention will be explained with reference to the vector diagram shown in FIG. First, an original color burst signal synchronized with the color burst signal of the original input video signal is applied to the input terminal 10. The original color burst signal is converted by a phase shifter 11 into a color burst signal e1 having a phase difference of 90 degrees. One of the outputs of the phase shifter 11 is converted by an inverting amplifier 12 into a color burst signal e2 having a phase difference of 180 degrees from the color burst signal e1. This color burst signal e2 has a phase difference of -90° with respect to the original color burst signal. These color burst signals e1 and e2 are combined by a volume 13, and a variable terminal of the volume 13 has a phase difference of 90 degrees with respect to the original color burst signal, and the amplitude can be varied depending on the position of the variable terminal. A color burst signal e3 is obtained. The color burst signal e3 and the original color burst signal are added to an adder circuit 14,
A color burst signal e4 is obtained. Here, the color burst signal e3 output from the variable terminal of the volume 13
Assuming that the amplitude of the color burst signal e4 can be changed to the same amplitude value as the original color burst signal, the color burst signal e4 output from the adder circuit 14 becomes a color burst signal having a phase difference in the range of ±45° with respect to the original color burst signal. The limiter 15 is used to maintain a predetermined amplitude constant.

Here, if a middle point click is provided on the volume 13 so that a phase difference of 0° can be specified, the output amplitude of the inverting amplifier 12 can be adjusted to finely adjust the phase difference to 0° at the hollow click point. Since there is no need to finely adjust the constants of inductance, capacitor, delay line, etc., which have large variable elements, and there is no need to finely adjust the phase, a stable midpoint click point can be obtained. That is, in this case, as shown in the vector diagram of FIG. 2, the output at the middle click point of the volume 13 is point A.

Furthermore, if an amplifier is provided after the variable terminal of the volume control 13 and the amplitude of the signal applied to the variable circuit 14 is increased, a color burst signal having a phase difference in a larger range than the above-mentioned ±45° range can be obtained. It will be done.

〔Effect of the invention〕

As described above, according to the present invention, a color burst signal whose amplitude can be varied with a phase difference of 90 degrees with respect to the original color burst signal is obtained using a one-stage phase shifter and an inverting amplifier, and is added to the original color burst signal. Since the configuration is configured to obtain a color burst signal with a desired phase difference in addition to the circuit, a desired hue adjuster can be obtained with a simple configuration that has few variable factors due to environmental changes such as temperature and humidity, changes over time, etc.

Further, with this configuration, even if a midpoint click indicating a phase difference of 0° is provided, it can be easily set by only fine adjustment of the amplitude, so a click point with fewer variable elements can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a hue adjuster according to an embodiment of the present invention, Fig. 2 is a vector diagram of each part to explain the operation of Fig. 1, and Fig. 3 is a block diagram showing a conventional hue adjuster. , FIG. 4 shows a vector diagram of each part for explaining the operation of FIG. 3. 1, 2, 11... Phase shifter, 3, 13... Volume,
12... Inverting amplifier, 14... Adder circuit, 15... Limiter.

Claims (1)

[Scope of Claims] 1. A hue adjuster that varies the phase with respect to a first color burst signal of an original input video signal, comprising: a) a phase shift with a predetermined phase difference with respect to the first color burst signal; b) variable means capable of varying the output of the phase shifting means from positive phase to negative phase; and c) adding means for adding the second color burst signal of the variable means and the first color burst signal. Hue adjuster with and.