JPH06253316A - System discriminating circuit - Google Patents

Abstract

PURPOSE:To provide a system discriminating circuit for a television signal which is suitable for IC-implementation. CONSTITUTION:A specific frequency of a color burst signal supplied to an input terminal 2 is passed or attenuated by a filter circuit 2. A peak detecting circuit 3 as a following stage detects the peak of the output voltage of the filter circuit 2 and a peak holding circuit 4 holds the peak level. A reference voltage Vref is generated from the voltage held by the peak holding circuit 4, and a voltage source 5 and resistances R1 and R2. A comparator 6 compares the reference voltage Vref with the output voltage of the filter circuit 2 and outputs a system decision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal system discriminating circuit used in a television receiver or a video tape recorder.

[0002]

2. Description of the Related Art A conventional television signal system discriminating circuit is disclosed in Japanese Patent Publication No. 63-7712, and FIG. 8 is a circuit diagram showing this system.
In FIG. 8, the video signal applied to the input terminal 20 is
The burst gate circuit 21 extracts only the burst signal by the burst gate pulse applied from the input terminal 22 and supplies it to the filter circuit 23.

As shown in FIG. 9, the filter circuit 23 attenuates a color burst signal of a specific frequency to give an amplitude difference between the color burst signals. The attenuated signal component and the non-attenuated signal component output from the filter circuit 23 are supplied to the multiplier circuit 24. The multiplier circuit 24 having a square characteristic squares the color burst signal that has passed through the filter circuit 23, expands the amplitude ratio of the attenuated signal component and the non-attenuated signal component, and supplies the expanded signal to the slicer circuit 25.

The slicer circuit 25 attenuates the attenuated signal component of the color burst signal and expands the amplitude ratio with the non-attenuated component, further expands the amplitude ratio of the color burst signal and supplies it to the tuning amplifier circuit 26. . The tuning amplifier circuit 26 uses the resonance circuit 26a as a tuning point at fH / 2. SECA
Comparing the cases of the M method and the PAL method, in the case of the SECAM method, the fH / 2 signal component as shown in FIG. 9B is obtained according to the attenuation ratio of the color burst signal as shown in FIG. 9A. However, since there is no attenuation in the PAL system, the fH / 2 signal component cannot be obtained.

In the signal discriminating circuit 27, the output of the tuning amplifier circuit 26 is converted into a direct current level by performing rectification or detection, and appears as a high or low level at the output terminal 28. The system of the television signal can be discriminated by the change in the level of the output terminal 28.

In the conventional television signal system discriminating circuit, since the tuning circuit 26a of the tuning amplifier circuit 26 which tunes to fH / 2 and amplifies is composed of the coil L and the capacitor C, it is difficult to make it into an IC. there were.

[0007]

The above-mentioned conventional signal discriminating circuit has a problem that it is necessary to attach an LC circuit for fH / 2 resonance to a tuning amplifier circuit, which is not suitable for use as an IC.

An object of the present invention is to provide a system discriminating circuit capable of discriminating a television signal without using a tuning circuit including a coil L and a capacitor C.

[0009]

According to the present invention, a filter circuit causes an amplitude difference between color burst signals, and a color burst signal having an amplitude difference is subjected to peak detection and hold by a hold circuit, and a hold voltage or a hold voltage. The reference voltage generated from the above and the detection signal are compared by a comparator to generate a discrimination signal.

[0010]

By the means described above, since only the SECAM system causes an amplitude difference for each line, the system of the television signal can be discriminated by comparing with the reference voltage.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Color burst signal extracted from video signal,
Supply to input terminal 1. In the filter circuit 2, the color burst signal supplied from the input terminal 1 is attenuated at a specific frequency so as to have an amplitude difference between the color burst signals. For example, pass band at 4.4 MHz, 4.25
The attenuation range is MHz. In the SECAM method, the frequency of the color burst signal is 4.25 MHz and 4.4 for each 1H.
Since the frequency is switched at MHz, aa and a in FIG.
As shown in b, an amplitude difference occurs every 1H.

The output of the filter circuit 2 is connected to the peak detection circuit 3
, And the detection signal shown in FIG. 2 (b) is obtained. Further, the peak hold circuit 4 obtains the peak hold voltage Vp shown in FIG. This peak hold voltage Vp
A predetermined reference voltage Vref is obtained by dividing the resistors R1 and R2 based on the voltage source 5 which is the lowest potential of the detection signal in (b). The reference voltage Vref when the ratio of the resistors R1 and R2 is set to 1: 2 is as shown by the dotted line in FIG. 2 (c).

The comparator 6 compares the reference voltage Vref with the detection signal of the peak detection circuit 3, and charges and discharges the capacitor 7 each time. By setting to discharge when the detection signal is larger than the reference voltage and set to charge when it is smaller,
In the SECAM method, charging / discharging is repeated every 1H. At this time, if the charging current is larger than the discharging current, the output terminal 8 becomes high level.

On the other hand, since the frequency of the color burst signal in the PAL system and the NTSC system is constant, FIG.
There is no amplitude difference as in (a). The peak detection signal of the peak detection circuit 3 has the waveform shown in FIG. The peak hold voltage Vp and the reference voltage Vref at this time are as shown in FIG. In this case, the capacitor 7 continues to be discharged and the output terminal 8 becomes low level. The system of the television signal can be discriminated from this level difference.

This embodiment does not require a tuning circuit for tuning to fH / 2 and can be used for SECAM and PA.
Since it is possible to discriminate between L / NTSC systems, it is possible to configure a circuit for system discrimination suitable for IC implementation.

FIG. 4 shows another embodiment of the present invention. In this embodiment, the reference voltage Vre is set by the fixed offset 40 through which the DC power source is connected in series to the peak hold circuit 4.
f is realized, and the reference voltage Vref is always set lower than the peak hold voltage Vp by a constant value.

Peak hold voltage V in case of SECAM
The relationship between p and the reference voltage Vref is as shown in FIG. 5 (a), and for PAL / NTSC is as shown in FIG. 5 (b). Therefore, the level of the output terminal 8 is low in the case of SECAM and high in the case of PAL / NTSC, and it is possible to discriminate between these methods. The relationship between the peak hold voltage Vp and the reference voltage Vref when no signal is input is shown in FIG.
As shown in (c), it is possible to surely make a determination even when no signal is input.

Although the peak hold voltage Vp and the reference voltage Vref are at the same level in the embodiment of FIG. 1 at the time of no signal input, the system cannot be discriminated, but this embodiment can surely discriminate even at the time of no signal input.

FIG. 6 shows another embodiment of the present invention. The same parts as those in FIG. The color burst signal applied to the input terminal 1 is given an amplitude difference by the filter circuit 2. The output is subjected to peak detection by the peak detection circuit 3 and applied to the sample hold circuit 61.

The sample hold circuit 61 has an input terminal 6
The sampling point is controlled on the basis of the fH / 2 pulse signal shown in FIG. 7 (a), which is given to No. 2, and holds the sample voltage Vs in a 2H cycle as shown in. The comparator 6 compares the sample voltage Vs with the magnitude of the detection signal of the peak detection circuit 3, and charges and discharges the capacitor 7 each time. When the output terminal 8 of the comparator 6 becomes low level, the low level detector 63 detects it and the phase shift circuit 64 shifts the sampling point of the sample hold circuit 61 by 1H.

As a result, if the SECAM system is used, the pulse signal shown in FIG.
Even if the sampling point is mistaken as shown in (b), it is shifted by 1H in the next sampling.
With such a pulse signal, sampling is performed correctly as shown in FIG. On the other hand, PAL and NTSC
Then, the sample voltage does not change even if the sampling point changes.

In this embodiment, it is of course possible to construct a system discriminating circuit suitable for IC, and it is possible to further improve the discriminating accuracy by applying feedback.

In the above embodiment, the system discrimination between SECAM and PAL / NTSC is described.
The distinction between NTSC and NTSC is made at another location, and the description of this portion is omitted.

[0024]

As described above, according to the system discriminating circuit of the present invention, it is possible to discriminate a highly accurate signal suitable for IC without requiring an external component such as an LC circuit. .

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the circuit operation of FIG. 1 when the input signal is a SECAM system.

FIG. 3 is a waveform diagram for explaining the circuit operation of FIG. 1 when the input signal is the PAL system.

FIG. 4 is a circuit configuration diagram for explaining another embodiment of the present invention.

5 is a signal waveform diagram for explaining the operation of FIG.

FIG. 6 is a circuit configuration diagram for explaining another embodiment of the present invention.

FIG. 7 is a signal waveform diagram for explaining the operation of FIG.

FIG. 8 is a circuit configuration diagram showing a conventional system discrimination circuit.

9 is a signal waveform diagram for explaining the operation of FIG.

[Explanation of symbols]

2 ... Filter circuit, 3 ... Peak detection circuit, 4 ... Peak hold circuit, 5 ... Voltage source, 6 ... Comparator, R1, R2 ...
Resistance, 40 ... Fixed offset, 63 ... Low level detector,
64 ... Phase shift circuit.

Claims (2)

[Claims] 1. A filter circuit for passing or attenuating a specific frequency of a supplied color burst signal, a hold circuit for holding an output voltage of the filter circuit, and a reference based on the voltage held by the hold circuit. A signal discriminating circuit comprising: a voltage generating circuit for generating a voltage; and a comparator for comparing the reference voltage with the output voltage of the filter circuit to generate a discriminating signal. 2. A filter circuit for passing or attenuating a specific frequency of a supplied color burst signal, a detection circuit for detecting the peak, and an output voltage of the detection circuit for fH / 2 period (fH: horizontal synchronizing frequency). ) Sample and hold circuit, a comparator for comparing the output voltage of the detection circuit and the sample voltage of the sample and hold circuit, and the sampling phase of the sample and hold circuit is shifted according to the output signal of the comparator. A system discriminating circuit comprising a phase shift circuit.