JPS58141092A - Automatic system switching circuit of color television receiver - Google Patents

Abstract

PURPOSE:To obtain a circuit which switches image receiving circuits automatically according to a reception system by providing a phase detecting means for system decision which decides on a PAL or an NTSC system, and a system switching means for automatic switching according to a phase detection output. CONSTITUTION:During reception on the PAL system, respective system changeover switches 19, 20, 21, and 22 are changed over to PAL system contacts P automatically according to the output of a phase detector 18 and respective demodulated color difference signal outputs B-Y, R-Y, and G-Y are led out of demodulators 13 and 14, and a matrix circuit 15. In this state, when a signal on the NTSC system is received, a burst gate circuit 8 separates a burst signal on an axis B-Y, which is inverted by a PAL switch circuit 17 and then supplied to a phase detector 18 for system decision to perform phase detection regarding a subcarrier. At this time, the output of the phase detector 18 goes down to ''0'' and the respective changeover switches 19, 20, 21, and 22 are switched to NTSC system side contacts N automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic system switching circuit in a color television receiver that can receive both PAL and NTSC color television broadcasts. Method and NT
There are places where you can receive both SC color television broadcasts. In such places, a color television receiver that can receive both types of broadcasting is required. Alternatively, when images reproduced on a video tape recorder or video disc device are displayed on a color television receiver, images recorded in both the PAL system and the NTSC system can be received on one color television receiver. A receiver is desired.

SUMMARY OF THE INVENTION Therefore, the present invention provides an automatic method switching circuit for automatically switching the image receiving circuit according to the received method in a color television receiver capable of receiving both PAL and NTSC color television broadcasts.

The present invention will be described below according to embodiments shown in the drawings. 1st
The figure shows one embodiment of the invention, where 1 is I
H delay line, 2 is a 180° inverter, 3.4 is an adder, 5 is a phase detector, 6 is a 7-lip flop, and 7 is a PAL switch circuit, which are especially used to demodulate PAL color television signals. These circuits were used in the 1990s, and are individually well-known circuits.

Further, 8 is a burst gate circuit, 9 is an APC phase detector, 10 is a low-pass filter, 11 is a VCO (voltage controlled oscillator), 12 is a 90° phase shifter, 13 is a B-Y demodulator,
14 is an RY demodulator, and 15 is an I''i matrix circuit, which are individually well-known circuits that are commonly used to demodulate color television signals of both the PAL system and the NTS and C systems. .16 is a well-known hue adjuster especially for adjusting the hue of NTSC color television signals.

Note that in the case of a PAL color television signal, there is no need to perform hue adjustment, so such a hue adjuster is unnecessary.

17 to 22 are used especially to configure the automatic switching circuit according to the present invention, 17 is a PAL switch circuit, 18 is a phase detector for system discrimination, 19.20
．． 21 and 22 are system changeover switches.

In the circuit configured as described above, first, when receiving PAL color television broadcasting (PAL VT
To explain the operation (including when playing an R tape or video disc), the burst gate circuit 8:
Only the burst signal component BI B2 is separated from the chroma signal based on the horizontally periodic gate pulse as shown in FIG.

In the case of the PAL system, the phase of this burst signal is inverted by ±45° with respect to the B-Y axis for each IH as shown in Figure 2. It is also supplied to the PAL switch circuit 17 and the phase detector 5.The phase detector 9 is connected to the AP (, #-
from VCOll as shown in Figure 2.
A subcarrier Sc that coincides with the Y axis is oscillated.Meanwhile, in the PAL switch circuit 17, the phase of the burst signal is inverted by 180 degrees every IH based on the output of the flip-flop 6.The flip-flop 6 is now in a steady operating state. If the output of the reed has a normal phase relationship, Fig. 2■
Among the burst signals B, .B, shown in FIG. This burst signal is supplied to the phase detector 18 for system discrimination, where V
Phase detection is performed with the subcarrier Sc from COII, and at this time, a positive voltage is output from the phase detector 18.Based on the positive voltage output of the phase detector 18, the mode changeover switch 19.
20, 21, and 22 are both automatically switched to the PAL method contact ■. Therefore, in this case, the chroma signal added and subtracted from the pre-IH chroma signal delayed through the IH delay line 1 in the adder 3.4 is The signal is supplied to the BY demodulator 13 and the RY demodulator 14 via system selector switches 19 and 20. Also, this B-Y demodulator 13 has vC
The subcarrier Sc obtained from As a result, a B-Y color difference signal is derived from the demodulator 13. On the other hand, the R-Y demodulator 14 receives a sub signal whose polarity is alternately inverted every sunset<IH as shown in FIG. A carrier wave S c %Sc is supplied, and an RY color difference signal is derived from the demodulator 14. At this time, P
Subcarrier 5cSSc' obtained from the AL switch circuit 7
is supplied to the phase detector 5, and based on this, the peak signals B1 and B2 shown in FIG. 0 is output. In this case, the flip-flop 6 is controlled to be alternately inverted based on the gate pulse in a normal phase relationship corresponding to the phases of the burst signals B8 and B2. If the phase of the flip-flop 6 is reversed for some reason,
A negative voltage is output from the phase detector 5, and the flip-flop 6 is immediately reversed to return to the original normal phase relationship, and this state is maintained from then on.In this way, when receiving PAL color television broadcasting, each system selection switch is activated. 19, 20, 21, and 22 are automatically switched to the PAL side contact [F] according to the output of the phase detector 18, and each demodulator 13, 14 and matrix circuit 1
B-Y demodulated from 5.

R-y and G-Y color difference signal outputs are derived.

However, when receiving NTSC color television broadcasting under such conditions, the node gate circuit 8
As shown in Figure 2 @ - Burst signal B on the Y axis
is separated and inverted for each IH in the PAL switch circuit 17 as shown in FIG. Phase detection is performed. At this time, the output of the phase detector 18 becomes O, which causes each method selection switch 19.2
Both 0.21.22id are automatically switched to the NTSC method side contact ■. In this case, the output of the phase detector 18 is always O regardless of the output phase of the flip-flop 6.

Therefore, in this case, the chroma signal is switched to the method selector switch 19.
20 directly to the B-Y demodulator 13 and the R-Y demodulator 14, and also the subcarrier Sc obtained by the VCO.
is adjusted to a normal phase by the hue adjuster 16, and then supplied to the R-Y demodulator 14 via the system selector switch 21, 22, and shifted in phase by 90° via the 90° phase shifter 12. As a result, when receiving NTSC color television broadcasting, each system selector switch 19, 20, 21, 22 automatically switches to NTSC according to the output of the phase detector 18. The demodulated color difference signal outputs are derived from the demodulators 13 and 14 and the matrix circuit 15.

In the above embodiment, each method selector switch 19.2
0.21.22 are shown as mechanical switches in order to facilitate switching operations, but in reality they may be constructed with electronic switching circuits.

According to the present invention, as described above, PAL system and NTSC
In color television receivers that can receive color television broadcasts from both systems, the receiver circuit can be automatically switched according to the received system, so there is no need to change the switch for each reception system, making it convenient. is 0

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the embodiment.

Claims (1)

[Claims] 1. In a color television receiver that can receive both PAL and NTSC color television broadcasts,
A color television equipped with phase detection means for detecting the phase of a burst signal and discriminating between PAL and NTSC, and system switching means that automatically switches according to the output of the phase detection means. Automatic system switching circuit in a television receiver.