JPS6033792A - Secam system color discriminating signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain the detected output of a stable SECAM system color discriminating signal even at the reception in a weak electric field by applying limiter and FM detection after inserting a prescribed frequency signal close to a chrominance subcarrier before and after a color discriminating signal. CONSTITUTION:A switch circuit 13 is inserted between an input terminal 1 and a limiter 2, and a signal having a prescribed frequency (4.43MHz) close to the chrominance subcarrier of the SECAM system is inputted to another input terminal 12 of said switch circuit 13. Said switch circuit receives a synchronizing signal from a synchronizing signal input terminal 10, transmits a reception signal from the input signal terminal 1 during the period of the color discriminating signal (c) in a horizontal blanking period, gives a signal H from the input terminal 12 to the limiter 2 during other periods T1, T3 other than the horizontal blanking period, and after the amplitude is limited, the result is detected by an FM detector 3. Since the noise before and after the color discrimination signal is replaced to a prescribed frequency signal and the amplitude is limited, a stable detected output is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an 8ECAM system for stably detecting received color discrimination signals in the SECAM system of television broadcasting.
The present invention relates to a color discrimination signal processing circuit.

In general, the composite video signal of the SECAM television signal includes a horizontal synchronizing signal A, a video signal B, and a signal called an 8ECAM color discrimination signal C, as shown in the waveform diagram in Figure 1 (ta). The color discriminating signal ζp is composed of an unmodulated color subcarrier inserted at the trailing edge of the horizontal retrace period.

Conventionally, this SECAM color discrimination signal is processed by a circuit as shown in FIG. 2, and its operating waveforms are shown as shown in FIG. The composite video signal is capacitively coupled by a capacitor CI, and the luminance component is removed as shown in FIG. It becomes a signal with a constant amplitude, which is detected by the next FM detection circuit 3 and sent to the output terminal 4.
Outputs the detection output to.

However, this horizontal retrace period has a period Dt- in which there is no signal of the frequency targeted by the FM @ wave other than the period in which this SECAM method color discrimination signal exists. ), noise E is often superimposed on the period C and the color discrimination signal C. If such a color discrimination signal is amplitude limited by the limiter circuit 2 and subjected to FM detection, an unstable detection output (FIG. 1(d)) will be obtained.

Originally, the detection output of the SBCAM color format 31J signal was SE.
Conventional 8ECAM color discrimination signal processing circuits are used to determine whether a CAM television signal is being received and to set the white level, which is the most important standard for reproducing 5D electric signals. When the color is weak, the reproduced color may be unstable or S
This method has the disadvantage of causing malfunctions in ECAM method determination.

Note that it is possible to connect a filter that removes noise components to the FM detection output of this color discrimination signal to reduce fluctuations in the output, but as shown in Figure 1 (d), it is possible to reduce the time constant of the filter. If you increase the filter time constant to reduce the influence of noise, you will get a signal F with poor transient characteristics during the scanning period.On the other hand, if you reduce the filter time constant to 1, you will get a signal G with good transient characteristics but the noise component cannot be removed sufficiently! I's reciprocal □It has the disadvantage that it is difficult to select the filter constant.

An object of the present invention is to provide a SECAM color discrimination signal processing circuit that eliminates such drawbacks and obtains a detection output of a SECAM color discrimination signal that is completely unaffected by noise even when receiving in a weak electric field. There is a particular thing.

The SECAM color discrimination signal processing circuit of the present invention converts a signal obtained by removing a luminance component from a received SECAM one-type composite video signal and a constant frequency signal close to the color subcarrier frequency used in this 8BCAM method into a predetermined manner. a switch means for switching according to a switching signal, and a switching signal for switching the constant frequency signal to a region before and after the color discrimination signal within the horizontal retrace period in synchronization with a synchronization signal of the SECAM composite video signal, and the switch and switching signal generating means for supplying the switching signal to the switching means.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention.

4(a) to 4(f) are signal waveform diagrams of FIG. 3. This embodiment differs from the conventional configuration in that the switching signal generation circuit 1
1 and a switch circuit 13 are added. The switching signal generating circuit 11 generates a switching signal (fourth switch circuit 13) synchronized with a synchronization signal (FIG. 4(C)) inputted from a synchronization signal human input terminal 12. Figure (d)) All occurred.

This signal is sent to the switch circuit 13. This switching signal is the period T of the color discrimination signal C during the horizontal retrace period of the composite video signal.
This signal has a low potential at 2 and a high potential at other periods TI and T3. This switch circuit 13 is supplied with a color discrimination signal (Fig. 4+8) which is capacitively coupled and has a luminance signal removed as in the conventional case, while a constant frequency signal (4.43 MHz) close to the color subcarrier of the 8ECAM system is input to the switch circuit 13. The signal (FIG. 4(b)) is input from the human-powered controller 2.

This switch circuit 13 is connected to a switching signal (see FIG. 4(a)) from an input terminal 1 to a manually input horizontal retrace period signal (see FIG. 4(a)).
A constant frequency signal (FIG. 4(b))' is switched and inserted into the front period Tl and the rear period T3 of d)). As a result, the color discrimination signal received during the central period T2 of the color discrimination signal is output to the output terminal of the switch circuit 13, and the remaining periods T1 and T3 are composite waveforms (Fig. 4(e) )) is output. This composite waveform is amplitude limited by a limiter circuit 2 similar to the conventional one, and then subjected to FM detection by an FM detector 3. At this time, the noise before and after the color discrimination signal is replaced with a signal of a constant frequency, and the noise component of the color discrimination signal itself is reduced by a limiter circuit, so it is stable without any transient phenomenon when detecting noise. A detected output of a color discrimination signal (FIG. 4(f)) is obtained.

As described above in detail, the present invention detects stable SECAM color discrimination signals even during reception in a weak electric field, and is therefore effective in good color reproduction and stable reception.

[Brief explanation of the drawing]

Figures 1 (a) to (d) are signal waveform diagrams of a conventional SECAM color discrimination signal processing circuit, Figure 2 is a block diagram of a conventional 8ECAM color discrimination processing circuit, and Figure 3 is an implementation of the present invention. The block diagram of the example, FIGS. 4(a) to 4(f), are signal waveform diagrams of each terminal according to this embodiment. In fig. i, 10.12... Signal manual terminal, 4...
...Output terminal, 2...Limiter circuit, 3...
...FM wave circuit. 11...Switching signal generation circuit, 13...
Switch circuit, A...Horizontal synchronization signal, B...
...Video signal, C...SECAM color discrimination signal, D...No signal period. E: Noise, F: Signal with a large time constant. G...Signal when the time constant is small, H...
...is a constant frequency signal. Built 1 figure rod Z times

Claims (1)

[Claims] a switch means for switching between a signal obtained by removing a luminance component from a received 8ECAM composite video signal and a constant frequency signal close to a color subcarrier frequency used in the 8ECAM format, using a predetermined switching signal; a SECAM system comprising a switching signal generation means for forming the switching signal for switching the constant frequency signal in the region before and after the color discrimination signal within the horizontal retrace period in synchronization with a synchronization signal of the signal, and supplying the switching signal to the switching means. Color discrimination signal processing circuit.