JPS6324783A - Signal discriminating circuit - Google Patents

Abstract

PURPOSE:To decrease the number of externally fitting parts by detecting, with the synchronization detection, a signal component in which a frequency included in the FM demodulating output of a burst signal is fh/2 (fh is a horizontal scanning frequency.) and discriminating a signal. CONSTITUTION:A synchronizing detecting signal Syd is formed in which a frequency synchronized to a horizontal scanning frequency fh is fh/2 by a frequency-dividing circuit 14. The burst signal of a reproducing chroma signal Cpb is FM-demodulated by an FM demodulating circuit 25 and a synchronizing detecting circuit 30 executes the synchronization detection with the signal Syd. A level discriminating circuit 33 detects that the signal level of a synchronizing detecting output supplied from the synchronizing detecting circuit 30 through a polarity inverting circuit 31 is a prescribed level or above, and outputs the obtained discriminating output as the discriminating output signal of an SECAM system television signal from a signal output terminal 34.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal discrimination circuit that discriminates whether an input television signal is a SECAM system television signal. N
The so-called multi-standard type for overseas regions, which is compatible with various standard television systems such as the TSC system, is commonly used in color television receivers, video tape recorders, and the like.

[Summary of the invention]

The present invention provides a signal discriminating circuit that discriminates whether an input television signal is a SECAM type television signal, by switching two color difference signals line-sequentially, and transmitting one color difference signal with a different transmission frequency for each scanning line. Frequency modulation (FM
) is converted into a luminance signal by SECAM.
By FM demodulating the unmodulated part, that is, the burst signal, which is added to the horizontal blanking part of the television signal of the system, the signal component whose frequency is fh /2 contained in the demodulated output is detected by synchronous detection. By doing so, a signal discrimination circuit is realized which is suitable for integration into an integrated circuit with a small number of external parts.

[Conventional technology]

Conventionally, color television receivers and video tape recorders for overseas regions have been using, for example, PAL, SE
There are so-called multi-standard type products that are compatible with various standard television systems such as , CAM, NTSC, etc., and it is necessary to determine which system the input television signal is.

Conventionally, two color difference signals (R-Y), , (B-Y) are switched line-sequentially for each scanning line (a carrier color signal obtained by frequency modulating (FM) a carrier wave with a different narrowing frequency is superimposed on a luminance signal). A signal discrimination circuit having a configuration as shown in FIG. 6 has been used to discriminate SECAM television signals.

In the conventional example of the signal discriminating circuit shown in the block diagram of FIG. It is taken out by the gate circuit 111. The burst signal is amplified by a preamplifier 112 and supplied to a detection circuit 114 via a ceramic filter 113, and is subjected to slope detection using the frequency characteristics of the ceramic filter 113 to obtain F M ijj 1m.

Here, in the SECAM system television signal, R-
4,40626 MHz carrier frequency for Y signal and B
- Since the carrier frequency of 4,2500 MHz for the Y signal is switched and used for each scanning line, when the burst signal superimposed on the horizontal blanking part is taken out and F M if S1m, the signal level is changed for each scanning line. An FM demodulated output is obtained in which the frequency at which rh increases and decreases includes a signal component whose frequency is 1/2 of the horizontal scanning frequency rh.

The detection output from the detection circuit 114, that is, the FMt and fil outputs for the burst signal, are supplied via a variable gain amplifier 115 to a tank circuit 116 whose tuning frequency is 1/2 of the horizontal scanning frequency fh of the SECAM television signal. and the frequency becomes f in the cough tank circuit 116.
A signal component of h/2 is extracted.

Then, a level discrimination circuit 118 to which the output of the tank circuit 116 is supplied via a low-pass filter 117 performs level discrimination of the output of the tank circuit 116, thereby determining the FMi! of the burst signal! It is determined whether or not the signal component of fh /2 is included in the XJI output, that is, whether or not the input television signal is a SECAM system television signal, and the determined output signal is sent to the signal output terminal 119. It is designed to output from.

[Problem that the invention seeks to solve]

By the way, by performing FM demodulation of the burst signal by slope detection using a ceramic filter, and extracting the signal component with a frequency of fh /2 in the FM9fi modulated output using a tank circuit, the SECAM system television signal can be obtained. In the conventional signal discriminating circuit that discriminates whether or not it is, when integrated into an integrated circuit, a large number of external components such as the ceramic filter and tank circuit are required.

In addition, a tank circuit whose tuning frequency is 1/2 of the horizontal scanning frequency fh of a SECAM television signal requires a tank coil with a large inductance, and there is a problem in that it requires a great deal of effort and time to adjust it. . Furthermore, in general, in many ceramic filters, the characteristics of each component provided are not constant, which is a factor that deteriorates the discrimination margin by the signal discrimination circuit.

Therefore, in view of the above-mentioned conventional problems, the present invention has been developed by
This patent is characterized by providing a signal discrimination circuit with a new configuration that can stably and reliably discriminate IECAM television signals and is suitable for integration into an integrated circuit with fewer external components. be.

[Means for solving problems]

In order to solve the above-mentioned problems, the signal discrimination circuit according to the present invention includes a gate circuit that extracts the unmodulated carrier portion of an input television signal, and a gate circuit that extracts the unmodulated carrier portion that is supplied via the gate circuit. An FM demodulation circuit that performs FM demodulation, a synchronous detection circuit to which the demodulated output from the FM demodulation circuit is supplied, and a synchronous detection signal having a frequency fh /2 synchronized with the horizontal scanning frequency fh of the input television signal. It is characterized by comprising a signal generation circuit that supplies the signal to the circuit, and a level discrimination circuit that discriminates the signal level of the detection output from the synchronous detection circuit.

[Effect]

In the signal discrimination circuit according to the present invention, the signal component having a frequency of fh /2 contained in the FM demodulated output of the unmodulated carrier portion of the input television signal is detected by a synchronous detection beam, so that the input television signal is It is determined whether the signal is a television signal or not.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

The embodiment shown in the block diagram of FIG. 1 is an example in which the present invention is applied to a chroma signal processing circuit of a PAL/SECAM video tape recorder with a variable speed playback function, and is a PAL system played back by a playback system (not shown). Or SECAM
Composite synchronization signal (Sync) of the television signal of the system
is supplied to the first signal input terminal 10, and a reproduced chroma signal (Cpb) is supplied to the second signal input terminal 20. In this embodiment, as shown in the timing chart of FIG. 2, a PAL television signal is reproduced in a reproduction system (not shown) during a period (T a ), and a SECAM television signal is reproduced during a subsequent period (Tb). The television signal of the PAL system is reproduced during the period (Tc), and the reproduced chroma signal (Cpb) of each system is supplied from the reproduction system to the second signal input terminal 20. shall be taken as a thing.

The composite synchronization signal (Sync) is supplied from the first signal input terminal 10 to a sample and hold (S/H) circuit 11. The S/H circuit 11 is supplied with the oscillation output of a voltage-controlled variable oscillator (VCO) circuit 13, which will be described later, as a sampling pulse, and receives a horizontal synchronization signal (I(D) of the composite synchronization signal (Sync)).
) part is sampled and held, and the sampled and held output is supplied as a control voltage to the 700 circuit 13 through the loop filter 12, and from the VCO circuit 13, a horizontal signal whose phase is locked to the horizontal synchronizing signal (HD) is supplied. It constitutes a PLL circuit that obtains an oscillation output at a scanning frequency (f h). Then, the oscillation output of the horizontal scanning frequency (fh) obtained from the VCOl path 13 is divided into 1/2 by the frequency divider 14.
By dividing the frequency, a synchronous detection signal (S yd) having a frequency of fh /2 in the form of a rectangular wave as shown in FIG. ing.

In this embodiment, the synchronous detection signal (Syd) is
The signal is supplied to a synchronous detection circuit 30, which will be described later.

Further, a second chroma signal (Cpb) is supplied to the second
The signal input terminal 20 of the switch circuit 22 is connected to the first fixed terminal 22a of the switch circuit 22 via a delay circuit 21 having a delay amount equal to one horizontal scanning period (11-1). The second fixed terminal 22b and the burst gate circuit 24 are connected. The switch circuit 22 has a movable terminal 22C connected to the signal output terminal 23, which selects the fixed terminals 22a and 22b in response to a control signal supplied to a control input terminal 22d from a level discrimination circuit 42, which will be described later. There is.

The burst gate circuit 24 extracts the unmodulated carrier portion, that is, the burst signal, of the reproduced chroma signal (Cpb) supplied from the second signal input terminal 20, and is capable of linear FM demodulation up to about 5 MHz. The burst signal is supplied to an injection O8C type FM demodulation circuit 25.

In the FM demodulation circuit 25, the burst gate circuit 2
The burst signal supplied from 4 is connected to the FMi summer tuning circuit 2.
By performing 5FM demodulation, the period (Ta), (T
c) There is an FM summer tone output with a constant signal level.
obtained for each H, and the period (Tb) of the SECAM method
Inside, an FM demodulated output whose signal level changes repeatedly every 1 tone is obtained.

Then, the 1jljl output from the FM demodulation circuit is sampled via an integral low-pass filter (LPF) 26.
It is supplied to the hold (S/H”) circuit 27, and this S
/11 Sampled and held in circuit 27.

The 378 circuit 27 samples and holds the peak level portion of the FMijj output for each LH. The sample-and-hold output from the 378 circuit 27 is DC-cut by a capacitor 28 and supplied to an AC amplifier 29, where the AC amplifier 29 amplifies it to a predetermined signal level and supplies it to a synchronous detection circuit 30.

The synchronous detection circuit 30 performs synchronous detection of the outputs of the two AC amplifiers using the synchronous detection signal (S yd) supplied from the frequency divider 14. The above synchronous detection circuit 3
0, as shown in Figure 2, the PA with a constant signal level
Period of L method (71”a).

During (Tc), the signal component of the synchronous detection signal (S yd) is output, and during the period (i″b) of the SECAM method in which the signal level repeatedly changes for each IH, the signal level remains constant. Detection output can be obtained.

Therefore, by detecting in the first level discrimination circuit 33 that the signal level of the synchronous detection output from the synchronous detection circuit 30 is at a predetermined level, the reproduced signal supplied to the second signal input terminal 20 is detected. Chroma signal (Cpb)
It is possible to detect that the signal is a S E CAM television signal.

In this embodiment, a state in which a variable speed reproduction operation such as still reproduction is performed in a reproduction system (not shown) and color arrangement inversion occurs in the reproduction output at a timing (to) during the period (Tb) of the SECAM method is assumed. This is shown in the timing chart of Figure 2, and by reversing the color arrangement, the phase of the signal component of the frequency fh /2 included in the FM demodulated output of the burst signal is reversed, and the polarity of the synchronous detection output is also reversed. There is.

In this embodiment, the detection output from the synchronous detection circuit 30 is supplied to a first level discrimination circuit 33 via a polarity inversion (INV) circuit 31 and a low-pass filter (LPF) 32, and is also supplied to a first level discrimination circuit 33 via a low-pass filter 41. and is supplied to the second level discrimination circuit 42.

The first drop discrimination circuit 33 includes the synchronous detection circuit 3
A discrimination output obtained by performing a level discrimination operation to detect that the signal level obtained by smoothing the synchronous detection output from 0 through the polarity inversion circuit 31 by the low-pass filter 32 is equal to or higher than a predetermined level (La). SIE
It is output from the signal output terminal 34 as a discrimination output signal of the CAM television signal, and the discrimination output is supplied to the reset terminal of the flip-flop circuit 43. The discrimination output signal outputted from the signal output terminal 34 is used to control the deactivation of an auto color killer circuit in a signal processing system for SECAM television signals.

Further, the second level discrimination circuit 42 performs a level discrimination operation to detect that the signal level of the detection output from the synchronous detection circuit 30 smoothed by the low-pass filter 41 is equal to or higher than a predetermined level (Lb). As a result, color arrangement inversion occurs in the reproduced chroma signal (Cpb) of the SECAM system, and the polarity of the synchronous detection output is inverted during a period (Tb).

) is detected and its discrimination output is supplied to the control input terminal of the polarity inversion circuit 31, so that the polarity inversion circuit 31 is configured to align the polarity of the synchronous detection output supplied to the low-pass filter 32. Further, the discrimination output from the second level discrimination circuit 42, that is, the color arrangement reversal detection output signal, is supplied to the trigger terminal of the flip-flop circuit 43, and the rising edge thereof, that is, the color arrangement reversal detection output signal is supplied to the second signal input terminal 20. The flip-flop circuit 43 is triggered every time a color arrangement inversion occurs in the reproduced chroma signal (Cpb) of the SECAM system. Then, the positive output pulse of the flip-flop circuit 43 is supplied as a control ffII signal to the control input terminal 22d of the switch circuit 22 to control the operation of the switch circuit 22, thereby compensating for the color arrangement inversion. The reproduced chroma signal (Cpb'') is outputted from the signal output terminal 23.

Note that in the first embodiment described above, by supplying the detection output from the synchronous detection circuit 30 to the polarity inversion circuit 31,
Although the reproduced chroma signal (Cpb) of the SECAM method is adapted to cope with the polarity inversion of the synchronous detection output by inverting the color arrangement, as in the second embodiment shown in FIG. Even if a double-wave rectifier circuit 51 is used to double-wave rectify the detected output from the synchronous detection circuit 30 and then supply it to the level discrimination circuit 33 via the low-pass filter 32, the first embodiment described above may be implemented. As in the example, SECAM is used as the discrimination output by the level discrimination circuit 33.
It is possible to obtain a discrimination output signal of the television system of the system.

Further, in the first embodiment described above, the common synchronous detection circuit 30 is used for discriminating the SECAM system television signal and detecting color arrangement reversal, but the synchronous detection circuit 30 shown in FIG.
As in the embodiment described above, separate synchronous detection circuits 30A and 30B may be used for the signal discrimination and color arrangement inversion detection.

In this third embodiment, a flip-flop circuit 43 is provided which is triggered by the rising edge of the discrimination output from the second level discrimination circuit 42, that is, the color arrangement detection output signal, and the positive output of this flip-flop circuit 43 is controlled. As a signal, the operation of the switch circuit 22 is controlled, and the input reproduced chroma signal (Cpb) is supplied to the burst gate circuit 24 via the switch circuit 22. Moreover, instead of providing the polarity inversion circuit 31 on the output side of the synchronous detection circuit 30A for signal discrimination, the synchronous detection circuit 30A
The synchronous detection signal (S yd) supplied to the phase inversion circuit 6
1, the phase inversion circuit 61
The operation is controlled by the discrimination output from the second level discrimination circuit 42, that is, the color arrangement inversion detection output signal.

In the third embodiment configured as described above, a variable speed reproducing operation is performed in a reproducing system (not shown), for example, as shown in the timing chart of FIG. 5 (tp).

Assuming that a reproduced chroma signal (Cpb) such that color arrangement inversion occurs at timing (tq) is supplied to the second terminal 20, the FM demodulation output of the burst signal superimposed on the reproduced chroma signal (Cpb) is is synchronously detected by the second synchronous detection circuit 30B using a synchronous detection signal with a frequency of fh /2, and the frequency extracted is fh /
The phase inverted portion of the signal component 2 is detected by the second level discrimination circuit 42, and the flip-flop circuit 43, which is triggered by the rising edge of the discrimination output, outputs an affirmative signal indicating the period during which the color arrangement is inverted. is obtained. Then, a burst gate circuit 24 extracts a burst signal F from a reproduced chroma signal (Cpb') whose operation is controlled by using the positive output of the flip-flop circuit 43 as a control signal, and which compensates for color arrangement inversion. M ('it g Regarding the FQ output, the first synchronous detection circuit 30A synchronously detects a signal component with a frequency of fh /2, and the first level discrimination circuit 33 detects that the signal level is higher than a predetermined level. By this,
The first level discrimination circuit 33 outputs a discrimination output signal indicating that the reproduced chroma signal (Cpb) supplied to the second signal input terminal 20 is a SECAM television signal.

In addition, in the timing chart of FIG. 5, a state in which the color arrangement remains inverted is indicated by a broken line, and the switch circuit 22
The actual state in which the above-mentioned color arrangement inversion is compensated for is shown by a solid line.

〔Effect of the invention〕

As is clear from the description of the embodiments described above, in the signal discrimination circuit according to the present invention, the frequency included in the input television signal jμ(r of the modulated carrier portion>(1g frequency output) is
By detecting the signal component of h/2 using synchronous detection, it is determined whether the input television signal is a SECAM television signal or not, so the operation for determining SECAM television signals is stable and stable. It can be operated reliably, and has few external parts, making it suitable for integrated circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the signal discrimination circuit according to the present invention, FIG. 2 is a waveform diagram showing the operation of the first embodiment, and FIG. 3 is a block diagram showing the operation of the first embodiment. FIG. 4 is a block diagram showing a second embodiment of the signal discrimination circuit according to the present invention, FIG. 4 is a block diagram showing a third embodiment of the signal discrimination circuit according to the present invention, and FIG. FIG. 3 is a waveform diagram showing an example operation. FIG. 6 is a block diagram showing a conventional signal discrimination circuit. 10.20...Signal input terminal 11.12...Sample/hold circuit 13...V
CO14... Frequency divider circuit 24... Burst gate circuit 25... FM? Summer tuning circuit, 30A...synchronous detection circuit 33...level discrimination circuit

Claims (1)

[Claims] A gate circuit for extracting an unmodulated carrier portion of an input television signal, an FM demodulation circuit for FM demodulating the unmodulated carrier portion supplied via the gate circuit, and demodulation by the FM demodulation circuit. a synchronous detection circuit to which an output is supplied; a signal generation circuit that supplies the synchronous detection circuit with a synchronous detection signal of a frequency fh/2 synchronized with the horizontal scanning frequency fh of the input television signal; It is equipped with a level discrimination circuit that discriminates the signal level of the detection output, and detects the signal component having a frequency of fh/2 included in the FM demodulation output of the unmodulated carrier portion of the input television signal by using synchronous detection. TV signal is SE
A signal discrimination circuit characterized in that it discriminates whether or not it is a CAM television signal.