JPH0332143Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention is particularly applicable to color television receivers.
This invention relates to a color television receiver capable of receiving PAL signals and NTSC signals, and in particular to its color signal switching circuit.

(B) Prior Art Hue adjustment in a PAL color television receiver is performed by supplying signals to each of the R-Y and B-Y demodulators, as shown in, for example, Japanese Patent Laid-Open No. 49-122619. This is done by differentially changing the amplitude of the color signal.On the other hand, in NTSC color television receivers, R-Y, B-
Since a color signal with the same amplitude must be supplied to each Y color demodulator, the above method cannot be used, so hue adjustment is performed by changing the phase of the color subcarrier supplied to the color demodulator. ing.

For this reason, the receiver uses a single color signal processing IC to receive PAL signals (PAL color television signals; the same applies to NTSC signals) and NTSC signals. In the aforementioned television receiver that performs PAL hue adjustment, a color signal switching circuit as shown in FIG. 2 was provided at the input section of the IC.

To explain Fig. 2, 1 is a PAL/
This IC is a color signal processing IC for NTSC.
Coupling capacitors C _{1 and} C ₂ are connected between the respective input pins 46 and 48 to the R-Y demodulator 2 and the B-Y demodulator 3 in the inner and the pair of carrier color signal input terminals 5 and 6, respectively.
and resistors R ₃ and R ₄ having resistance values close to each other are connected in series, and the resistor is connected between the input pins 46 and 48.
Resistors R ₅ and R ₆ with the same resistance value and variable resistor VR 1 which together _{with R 3 and R 4 constitute a voltage dividing circuit are connected in series, and the sliding terminal of this variable resistor VR 1 is connected to} a coupling capacitor C ₃ and switching transistor Tr ₁
The switch is connected to the ground via the base, and a switching signal is applied to the base thereof, which becomes high level when receiving a PAL signal and becomes low level when receiving an NTSC signal.

That is, in this conventional example, when receiving a PAL signal, the R-Y carrier color signal and the B-Y carrier color signal are input to the input terminals 5 and 6, respectively, and at this time, the switching transistor Tr ₁ is turned on. By changing the position of the slider of the variable resistor VR ₁ , the R-Y and B-Y carrier color signals appearing between both ends of the input resistors R ₁ and R ₂ having the same resistance value can be
Each of the amplitudes is subjected to partial voltage adjustment and input to each color demodulator 2, 3 in the IC 1, and hue adjustment is performed.

Also, when receiving NTSC signals, input terminals 5 and 6
Since the same carrier color signal including the R-Y component and the B-Y component is supplied to the input terminals 5 and 6, and the switching transistor _Tr1 is turned off at this time, the components of the carrier color signals at the input terminals 5 and 6 are The voltage ratios are substantially the same, and therefore, the respective color signals are input to the respective demodulators 2 and 3 with substantially the same amplitude.

(c) Problems to be solved by the invention By the way, in the conventional circuit described above, when receiving a PAL signal, the impedance of the switching transistor Tr ₁ and the capacitors C ₁ and C ₂ at the input pin 46 of IC 1 is ignored. A series path consisting of resistor R ₃ and a part of variable resistor VR ₁ is connected in parallel to resistor R 1, and when receiving an NTSC signal, the resistor R _{1 and} R ₃ are connected to pin 46. resistance R ₅ ,
The series paths of R ₆ , R ₄ , R ₂ and variable resistor VR ₁ are connected in parallel. Therefore, the input impedance of R-Y demodulator 2 when receiving an NTSC signal is
It is considerably louder than when receiving a PAL signal, and the B
The same applies to the -Y demodulator 3. This means that noise components other than the regular carrier color signal are likely to get onto the input lines 7 and 8 when receiving an NTSC signal.
Since this noise component is input to the color demodulators 2 and 3, there are drawbacks such as colors appearing on the screen and hue changes even when the color control volume is set to the minimum.

Therefore, this invention eliminates these drawbacks.
The purpose of the present invention is to provide a color signal switching circuit for a color television receiver capable of receiving both PAL/NTSC.

(d) Means for solving the problem In the color signal switching circuit of the present invention, R-Y, B-Y
The PAL hue adjustment variable resistor connected between the input terminals of each color demodulator is electrically disconnected from each of the input terminals when receiving an NTSC signal.

(E) Effect According to the above configuration, when receiving an NTSC signal, R-
Since the input terminals of the Y and B-Y color demodulators are not connected by the variable resistor, the impedance elements connected to each input terminal are independent, and therefore the input impedance of each demodulator is is prevented from increasing when receiving an NTSC signal.

(F) Embodiment FIG. 1 shows an embodiment of the color signal switching circuit according to the present invention, and parts corresponding to those in FIG. 2 are given the same figure numbers and their explanation will be omitted. In this embodiment, 9 and 10 are color control amplifiers.
The first and second input terminals, 11, to which the carrier color signal that has passed through the ACC amplifier are input, are a 1H delay line, and this delay line and a transformer 12, which functions as an adder/subtractor, are connected.
It constitutes a separation circuit for R-Y and B-Y carrier color signals when receiving a PAL signal. Note that when receiving an NTSC signal, the carrier color signal that has passed through the ACC amplifier etc. is inputted only to the second input terminal 10 by a switching circuit (not shown) or the like.

Such a configuration is exactly the same as the conventional case, and the feature of this embodiment is not this but the following point. That is, first and second switching transistors Tr ₂ and Tr ₃ are connected between both ends of a PAL hue adjustment variable resistor VR ₁ whose sliding terminal is directly grounded and the ground point. at a low level when receiving a PAL signal on the base of
The point is that a switching signal that becomes high level when receiving an NTSC signal is applied.

According to such a configuration, when receiving a PAL signal, the first
Since the second switching transistors Tr ₁ and Tr ₂ are both off, the R-Y and B-Y carrier color signals appearing across the respective input resistors R ₁ and R ₂ at this time are as shown in FIG. Just as in the conventional example,
The hue will be adjusted by variable resistor _VR1 .

On the other hand, since switching transistors Tr ₂ and Tr ₃ are both on when receiving an NTSC signal, the resistance
This means that the lower ends of R ₅ and R ₆ are separated from the variable resistor VR ₁ and directly grounded. Moreover, since the above-mentioned resistors R ₁ to _{R 6} are selected in exactly the same way as in the case of Fig. 2, when receiving an NTSC signal, the input resistors R ₁ ,
The same carrier color signals appearing between both ends of R ₂ are input to the color signal processing IC 1 with substantially the same amplitude.

Here, when receiving the NTSC signal, the impedances connected to the input pins 46 and 48 of IC1 are smaller by the amount of the variable resistor VR ₁ compared to when receiving the PAL signal, but this variable resistor VR _1
The resistance value _{of pins 46} ,
This means that the input impedance when receiving the NTSC signal at the 48 is reduced to approximately the same level as when receiving the PAL signal.

Note that the IC 1 also includes a color matrix circuit 4 for generating G-Y signals and various circuits attached to the color demodulators 2 and 3, but these points are not directly related to the present invention. I will omit the explanation.

(g) Effects of the invention According to the color signal switching circuit of the invention, the same color demodulator can be used both when receiving PAL signals and when receiving NTSC signals, and hue adjustment can also be performed when receiving PAL signals. In the color television receiver, the input impedance of the color demodulator is
It can be lowered in the same way as when receiving PAL signals, so
Noise is not input to the color demodulator when receiving an NTSC signal, and therefore color residue and hue shift when the color control volume is at its minimum in the receiving state can be eliminated.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a circuit diagram showing a conventional color signal switching circuit. R ₃ , R ₄ : Resistance as the first and second impedance elements, R ₅ , R ₆ : Resistance as the third and fourth impedance elements, VR ₁ : Variable resistor as variable impedance means, Tr ₂ , Tr ₃ : Switching transistor.

Claims (1)

[Scope of utility model registration request] In a color television receiver in which a PAL carrier color signal and an NTSC carrier color signal introduced via a common input line are demodulated by the same R-Y demodulator and B-Y demodulator, the control terminal A voltage dividing path is formed by connecting both ends of the variable impedance means for PAL hue adjustment, which is connected to the reference potential point, with first and second impedance elements inserted in series to the input lines to the respective demodulators. The third component
The variable impedance means is connected to each of the input lines via the fourth impedance element, and switching means are connected between both ends of the variable impedance means and the reference potential point, and each switching means is turned on when receiving an NTSC signal. A color signal switching circuit for a color television receiver, characterized in that: