JPH03295386A - Color television receiver - Google Patents

Abstract

PURPOSE:To demodulate a chrominance signal by means of a hue which is always constant and optimum by providing a circuit deciding the hue of a video output and hue correction means changing a control signal in accordance with the input route of a video signal. CONSTITUTION:In the video signal, there is a case when the rotation angles of the phase of a burst signal differ by a transmission route is the receiver and the rotation angles of the hue differ by the channel of an RF signal. In such a case, the rotation angle of the phase is previously measured and the size of the control signal equivalent to the rotation angle of the phase in the hue deciding circuit 65 is decided. Then, the hue correction means 11, 12, 15 and 16 change the size of the control signal given to the hue deciding circuit 65 in accordance with the route of the video signal inputted to the receiver or the reception channel by a previously decided quantity. Thus, the hue in the video output can always be made constant irrespective of an input source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hue control circuit used in a color television receiver.

An example of the configuration of a conventional NTSC color television receiver is shown in FIG. 4, and its operation will be briefly explained. From the radio waves received by the antenna 50, a television broadcast signal of a desired channel is selected by the l-s 51 and converted to an intermediate frequency. The intermediate frequency signal is amplified by an amplifier 52,
A detection circuit 53 extracts a composite video signal therefrom. After the composite video signal passes through the first video amplification circuit 54,
/C separation circuit 57 separates the signal into a luminance signal (Y) and a chroma (=color) signal (C). The processing of this chroma signal will be explained in detail below.

The chroma signal is amplified by a first chroma amplifier 61, and one of its outputs is input to a burst amplifier 66. Here, only the burst signal is extracted and amplified by the burst gate pulse. One of the outputs of the burst amplifier 66 is detected by the ACC detection circuit 67, and the gain of the first gloma amplifier 61 is controlled according to the output, so that the amplitude of the burst signal being output from the first gloma amplifier 61 is kept constant. It is controlled in a loop so that burst amp 66
The other output is input to the hue control circuit 65, where the phase of the burst signal is changed by an external control signal (DC control voltage). In the APC detector 64, the phase of the burst signal that has passed through the hue control circuit 65 and ■C○(
The voltage controlled oscillator (VCO 63) detects the difference in phase from the output signal of the VCO 63 and generates a DC voltage corresponding to the difference to control the phase of the oscillation signal of the VCO 63. Due to this closed loop, the output signal of ■C063 that matches the phase of the burst signal (after being adjusted by the DC control voltage in the hue control circuit 65) is
The signal is input to a chroma signal demodulation circuit 58. The above is the hue control effect. Regarding the color density, the control circuit 59 receives an external control signal (D
C control voltage).

In recent years, with the spread of video equipment such as VTRs (video tape recorders) and video discs, opportunities to directly input composite video signals to television receivers have increased. Furthermore, in order to reduce image quality deterioration of the video signal, the luminance signal (
A method of inputting the chroma signal (Y) and chroma signal (C) separately (this is called an "S-video signal") has also come to be used.When inputting various video signals in this way, television Inside the receiver, when receiving a broadcast signal from the antenna or when inputting a composite video signal,
The signal transmission path differs depending on the case where a video signal is input (dotted line in Figure 4).

In the case of the NTSC system, due to its nature, the degree of phase rotation that the burst signal receives from the circuit differs depending on the transmission path. For example, if the hue is adjusted to the optimum value when a television broadcast signal is received, a problem arises in that the hue deviates from the optimum value when a composite video signal or S-video signal is received from an AV device.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a television receiver that can always demodulate color signals with optimal hue regardless of the signal input system.

In order to achieve the above object, the present invention provides an NTSC color television receiver that can input a plurality of video signals passing through different routes inside the receiver.
It is characterized by comprising a circuit that determines the hue of the video output based on the phase of the color burst signal and an external control signal, and a hue correction means that changes the control signal according to the input path of the video signal. . Note that the hue correction means is
The hue may be changed depending on the receiving channel instead of depending on the input path of the video signal.

As mentioned above, the rotation angle of the burst signal phase of the video signal may differ depending on the transmission path within the receiver. Furthermore, the phase rotation angle differs depending on the RF multiple signal channel. In such a case, the phase rotation angle is measured in advance, and the magnitude of the control signal corresponding to the phase rotation angle in the hue determining circuit is determined. The hue correction means changes the hue of the video output from the input source by changing the magnitude of the control signal given to the hue determining circuit by the predetermined amount according to the path of the video signal input to the receiver or the receiving channel. It can be kept constant regardless of the

In general, the DC control voltage is generated by D/A converting a digital signal, or a constant DC voltage is varied using a variable resistor or the like.

FIG. 1(a) shows an example of a configuration to which the present invention is applied in the former case. Here, when converting a digital signal into a DC control voltage by the DAC (D/A converter) 11 and inputting it to the hue control circuit 65 shown in FIG. The DC control voltage is changed depending on the situation (different cases). Since the signal output from the DACll is generally a PWM modulated (pulse width modulated) signal, it is converted into a DC voltage by the integrating circuit 12.
The circuit shown in FIG. 1(a) switches the integral constant in accordance with information regarding the input system (AV switching signal) from the input signal switching switch (AV switching 5W) 16. A specific example of this configuration is shown in FIG.

The output A of the DAC is output from the transistor Tri, and is connected to the resistors R1 to R7, the capacitor 01, and the transistor Tr2.
is input to an integrating circuit configured by The transistor Tr2 of this integrating circuit receives the AV from the AV switching 5W16.
A switching signal is input, and this AV switching signal is Ll when the input system is a television broadcast wave (TV), and H when the input system is a video signal from an external AV device (AV).

When the AV switching signal is L (during TV reception), the transistor Tr2 is turned off, and the integrating circuit is constituted by the resistors R1 to R7 and the capacitor C1.

Therefore, the input terminal B of the DC control signal of the hue control circuit 65
A DC voltage determined by the DAC output and the values of each of these elements (resistors R1 to R7 and capacitor C1) is applied. On the other hand, when the AV switching signal is H (at the time of a large AV input, the transistor Tr2 is turned ON, which is equivalent to removing the resistor R7 from the integrating circuit. Therefore, the input terminal B of the hue control circuit 65 has the DAC output and the resistor R1~R6
A DC voltage determined by the value of the capacitor C1 is applied.

As a result, as shown in FIG. 3, even if the same output is given from the DAC, the value of the DC control voltage input to the hue control circuit 65 can be set differently depending on whether the input system is a TV or an AV. can. Therefore, by appropriately setting the value of the resistor R7, it is possible to compensate for the phase rotation of the burst signal in the path of each input signal, so that the optimal hue is always constant on the screen.

The present invention can be realized by various configurations in addition to the examples described above. FIG. 1(b) shows an example of a configuration in which after the integrating circuit 12 generates a DC voltage according to the DAC output, the DC voltage switching circuit 13 applies correction according to the AV switching signal. ing. Also,
Figure (C) is an example of a configuration in which a DC control voltage is directly generated using a variable resistor, etc., and as in the case of (b), D
The C voltage switching circuit 13 corrects the DC voltage according to the AV switching signal. Furthermore, (d) in the same figure shows a configuration example in which the digital signal for hue control input to the DAC II is switched (in the DAC control circuit 18) based on the switching signal (■) before converting to a DC voltage. There is.

Note that the hue correction may be performed not only for each AV input but also for each channel receiving the RF multiplied signal. In this case, a channel switching signal may be used instead of the AV switching signal on each side.

As explained above, according to the present invention, it is possible to demodulate a color signal at a constant, optimal hue and output it on the screen, regardless of the signal input system or reception channel. become able to.

[Brief explanation of the drawing]

Figures 1 (a) to (d) are block diagrams showing the configurations of various embodiments of the present invention, Figure 2 is a circuit diagram showing the specific configuration of a circuit that switches the integral constant according to the input system, and Figure 3 4 is a graph showing changes in the DC control voltage input to the hue control circuit, and FIG. 4 is a block diagram showing the flow of various signals in a conventional television receiver.

Claims (2)

[Claims] (1) In an NTSC color television receiver that can input multiple video signals that pass through different routes inside the receiver, the video output is controlled based on the phase of the color burst signal and an external control signal. A color television receiver comprising: a circuit that determines hue; and hue correction means that changes the control signal according to an input path of a video signal. (2) In an NTSC color television receiver, a circuit that determines the hue of the video output based on the phase of the color burst signal and an external control signal, and a hue that changes the control signal according to the receiving channel. A color television receiver comprising: a correction means.