JPH0613281U - Hue adjustment circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] It is intended to simplify an apparatus for converting an NTSC signal into a PAL signal. A phase shift means for shifting a chroma signal of an input NTSC system, a synthesizer means for extracting a chroma video signal from the output of the phase shift means and a burst signal from the chroma signal for synthesis. Means for balanced modulation of the signal obtained from the means.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a device for reproducing an NTSC signal recorded on a recording medium and converting it into a PAL signal by analog processing, and a VTR (video tape recorder) using the device.

[0002]

[Prior art]

 Some VTRs for areas using PAL system TV (television) signals convert NTSC system signals to PAL system signals and record them on PAL system TVs in NTSC system. We are making it possible to watch the recorded video image software.

As a conversion processing method for this purpose, considering an NTSC signal as shown in FIG. 4A, in order to convert the NTSC signal into the PAL system, only a burst signal is first converted by a phase shift circuit. The signal of FIG. 4B with the phase advanced by 45 ° is created. After that, a signal (2fsc) having a frequency twice that of the carrier wave used for reproduction and demodulation is created, and the phase of the 2fsc is adjusted to the U axis in FIG. 4B by the phase shift circuit. When the signal having the double phase carrier frequency and the chroma signal (fsc) shown in FIG. 4 (b) are input to the balanced modulator, the balanced modulator performs frequency conversion and outputs the difference component as shown in FIG. As shown in c), a signal inverted with respect to the U axis (a phase difference of 180 ° from fsc) is obtained. The signal component indicated by the broken line in FIG. 4 (c) appears as a third-order component (3fsc) that is the sum component generated as a result of the frequency conversion, and is applied to the U axis of the carrier frequency by the bandpass filter. It is possible to leave only the symmetrical components. Then, the signals of FIGS. 4 (b) and 4 (c) are switched every 1H period to be converted into a PAL system chroma signal.

[0004]

[Problems to be solved by the device]

 In the above conventional conversion method, in order to change the hue after conversion, it is necessary to change the phase of the burst signal and the phase of the carrier frequency doubled at the same time, which is a drawback that the initial setting at the time of design becomes complicated. there were.

Therefore, the present invention is intended to solve such a problem.

[0006]

[Means for Solving the Problems]

 Phase shifting means for shifting the chroma signal of the input NTSC system, synthesizing means for extracting the chroma video signal from the output of the phase shifting means and for synthesizing the burst signal from the chroma signal, and the synthesizing means. And means for performing balanced modulation on the obtained signal.

[0007]

[Action]

 According to the above means, in order to convert the NTSC system signal to the PAL system, only the chroma signal is phase-shifted.

[0008]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram of an essential part of a VTR embodying the present invention, and FIG. 2 is a vector diagram for explaining its operation. An NTSC system chroma signal is input to a terminal 1 and a terminal 2 receives the chroma signal. Receives a burst gate pulse, 2 fsc (fsc: color subcarrier) is input to the terminal 3, and 1/2 fH pulse is input to the terminal 4. Therefore, the first changeover switch 7 is controlled so as to select the terminal B during the burst gate pulse period and the terminal A during the other period, and the second changeover switch 9 is controlled by the 1/2 fH pulse every 1H period. Select terminals C and D alternately.

The chroma signal ((a) in FIG. 2) (B in FIG. 2 indicates a burst signal and C indicates a chroma video signal) input to the terminal 1 is transferred by 45 ° by the phase shift circuit 5. ((B) in FIG. 2) The signal is output to the terminal A and directly supplied to the terminal B. Then, the signal is selected by the switch 7 and the signal as shown in FIG. 2C is obtained from the switch 7. This signal C is directly applied to the terminal C of the switch 9 and supplied to the balanced modulator 8. A signal of 2fsc is applied to the terminal 3. The signal of 2fsc is made to have a phase as shown by the broken line in FIG. 2C by the phase circuit 6, and then the signal c is changed to 2fsc by the balanced modulator 8. The phase shown in FIG. 2 (d) is symmetrical with respect to the axis, and this is supplied to the terminal D of the switch 9. As a result, the chroma signal converted into the PAL signal is obtained from the switch 9, and this signal is output from the terminal 11 after the third-order component generated during the balanced modulation is blocked by the bandpass filter 10. The chroma signal output from the terminal 11 is set to 2fsc as the U axis.

FIG. 3 shows a specific example of the configuration of the phase shift circuit 5. The hue can be adjusted by changing the impedance of the FET 12 by a DC voltage from a variable resistor VR that can be operated from outside the VTR. I'm normalizing it.

[0012]

[Effect of device]

 As described above, according to the present invention, since the signal of the NTSC system is converted into the PAL system by only shifting the chroma signal, it is possible to simplify the configuration of the conversion device of this type.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an essential part of a VTR embodying the present invention.

FIG. 2 is a vector diagram for explaining the operation of FIG.

FIG. 3 is a specific configuration example of a block diagram of main parts of FIG.

FIG. 4 is a diagram for explaining a conventional signal conversion operation.

[Explanation of symbols]

 1 terminal 2 terminal 3 terminal 4 terminal 5 phase shift circuit 6 phase circuit 7 first changeover switch 8 balanced modulator 9 second changeover switch 10 bandpass filter 11 output terminal

Claims (2)

[Scope of utility model registration request] 1. A phase shift means for shifting the input chroma signal of the NTSC system, and a synthesizer means for extracting a chroma video signal from the output of the phase shift means and for extracting and synthesizing a burst signal from the chroma signal. A hue adjustment circuit including a means for performing balanced modulation on a signal obtained from the combining means. 2. A phase shifting means for shifting an input chroma signal of NTSC system, and a synthesizing means for extracting a chroma video signal from the output of the phase shifting means and for extracting and synthesizing a burst signal from the chroma signal. A video tape recorder provided with a hue adjustment circuit comprising a means for performing balanced modulation of a signal obtained from the synthesizing means.