JPH09322177A - Secam signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discriminate a SECAM chrominance signal without malfunction even when a black-and-white signal arrives by providing a level detection circuit. SOLUTION: The level of a SECAM signal from a limiter amplifier circuit 3 is detected and when it does not reach a certain level, it is discriminated that the incoming signal is not the SECAM signal. Assuming that the black-and- white signal arrives, for example, a level detection circuit 10 discriminates that the level of the input signal is low. Then, the level detector 10 forcedly switches the discrimination output signal of a SECAM signal discrimination circuit 7. Therefore, an output circuit 6 performs mute operating as a mute circuit. On the other hand, a microcomputer switches the system of whole VTR to any state except SECAM signal reception due to a discriminate signal provided at a terminal 8. Thus, even when the black-and-white signal arrives, the SECAM signal discrimination circuit 7 can discriminate any state except the SECAM signal without malfunction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to household VTRs and Ts.
The present invention relates to a SECAM signal processing circuit used for a V receiver, and in particular, an S equipped with a SECAM signal determining circuit for determining whether or not an incoming signal is a SECAM signal.
The present invention relates to an ECAM signal processing circuit.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional SECAM signal processing circuit for a VTR and shows a recording mode. An SECAM video color (chroma) signal for baseband recording is applied to the input terminal (1). The filter (2) is a bell filter and restores the frequency characteristic of the color signal.

The extracted color signals of 4.40 MHZ and 4.25 MHZ are
The signal is amplified by the limiter amplifier (3) so as to withstand the frequency division. The amplified color signal is frequency-divided by a quarter frequency dividing circuit (4) for low-frequency recording. The divided color signal is applied to the output circuit (6) after the unnecessary component is removed by the filter (5). The output circuit (6) operates as a mute circuit.

On the other hand, the output signal of the limiter amplifier (3) is determined by a SECAM signal determination circuit (7) as to whether it is a SECAM signal. The SECAM signal discriminating circuit (7) discriminates whether or not the signal is a SECAM signal by discriminating the frequency of the 4.40 MHz and 4.25 MHz color signals existing in the burst period. The discrimination output signal of the SECAM signal discrimination circuit (7) is applied to the output circuit (6) and is led out to the terminal (8).

[0005] The output circuit (6) operates as a mute circuit, and performs a mute operation when it is determined that the determination output signal of the SECAM signal determination circuit (7) is not a SECAM signal. As a result, no unnecessary signal is generated at the output terminal (9). Also, terminal (8)
Is applied to a microcomputer (not shown), and the microcomputer switches the entire VTR system to the SECAM recording state.

Therefore, according to the apparatus shown in FIG.
Recording and discrimination of color signals can be performed.

[0007]

However, in the apparatus shown in FIG. 2, when a black-and-white signal arrives, the SECAM color signal may be erroneously determined. That is, when a black and white signal arrives, the input signal of the limiter amplifier (3) becomes zero. Then, the limiter amplifier (3) performs an amplifying operation with no input, and the noise is amplified and output. When the amplified noise is applied to the SECAM signal discrimination circuit (7), the SECAM signal discrimination circuit (7) reduces the noise to 4.40 MHz.
There is a case where the frequency is erroneously determined to be the color signal frequency of Z, 4.25 MHz.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above points, and provides a SECAM signal processing circuit having a SECAM signal determining circuit for determining whether an incoming signal is a SECAM signal or not. A level detection circuit for detecting the level of the SECAM signal input to the SECAM signal discrimination circuit is provided, and the discrimination result of the SECAM signal discrimination circuit is switched according to the detection output signal of the level detection circuit. And

[0009]

1 shows a SECAM signal processing circuit according to the present invention, in which (10) detects the level of the SECAM signal in a limiter amplifier (3), and the SECAM signal is detected according to the detected output signal. This is a level detection circuit for switching the discrimination result of the signal discrimination circuit (7).

In FIG. 1, the same circuit blocks as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, the level of the SECAM signal from the limiter amplifier (3) is detected, and when it does not reach a certain level,
It is determined that the incoming signal is not a SECAM signal.

For example, when a black-and-white signal arrives, the level detection circuit (10) determines that the input signal is at a low level. The level detection circuit (10) is SECAM
The discrimination output signal of the signal discrimination circuit (7) is forcibly switched. For this reason, the output circuit (6) operates as a mute circuit as a mute circuit. In addition, the microcomputer switches the whole system of the VTR to a state other than the reception of the SECAM signal according to the determination signal obtained at the terminal (8).

Therefore, a SECAM signal discriminating circuit (7)
Does not malfunction even when a black-and-white signal arrives.
It can be determined that the state is other than the AM signal. Also, normal S
When the ECAM signal arrives, a signal of a sufficient level is detected by the level detection circuit (10). In this case, the discrimination output signal of the original SECAM signal discrimination circuit (7) may be generated as it is.

Various methods can be considered for switching the determination output signal of the SECAM signal determination circuit (7). For example, an AND gate of the discrimination output signal of the SECAM signal discrimination circuit (7) and the detection output signal of the level detection circuit (10) may be used. Further, if the SECAM signal discriminating circuit (7) is constituted by a differential amplifier, a signal for inverting the differential amplifier may be added to one of the two inputs of the differential amplifier. Also, the level detection circuit (1
SECAM signal to be added to 0) is a limiter amplifier (3)
Or an input signal of the limiter amplifier (3).

FIG. 3 is a specific circuit example of the limiter amplifier (3) and level detection circuit (10) of FIG. The limiter amplifier (3) includes, for example, amplifiers (11), (12), (1).
3). In FIG. 3, the output signal of the amplifier (11) is applied to the integrating circuit (14). Integrator (1
4) detects the average level of the input signal. The detected DC signal is applied to a comparator (16) via a buffer (15) and is compared with a reference voltage.

If the level of the input signal is high, an "H" level signal is generated at the output terminal (17). If the level of the input signal is low, an "L" level signal is generated at the output terminal (17). . Therefore, according to the circuit of FIG. 3, the level detection of the SECAM signal in the limiter amplifier (3) can be performed.

[0016]

As described above, according to the present invention, in a SECAM signal processing circuit having a SECAM signal discriminating circuit for discriminating whether or not an incoming signal is a SECAM signal, the level of the SECAM signal is detected. A level detection circuit is provided to perform the determination by the SECAM signal determination circuit according to the detection output signal of the level detection circuit.
There is no risk of malfunctioning the ECAM color signal determination.

[Brief description of drawings]

FIG. 1 is a block diagram showing a SECAM signal processing circuit of the present invention.

FIG. 2 is a block diagram showing a conventional SECAM signal processing circuit.

FIG. 3 is a detailed circuit diagram of a limiter amplifier (3) and a level detection circuit (10) of the present invention.

[Explanation of symbols]

 (3) Limiter amplifier (10) Level detection circuit

Claims (2)

[Claims] 1. An S equipped with a SECAM signal discriminating circuit for discriminating whether or not an incoming signal is a SECAM signal.
In the ECAM signal processing circuit, a level detection circuit for detecting the level of the SECAM signal input to the SECAM signal discrimination circuit is provided, and the discrimination result of the SECAM signal discrimination circuit is switched according to the detection output signal of the level detection circuit. SECAM signal processing circuit characterized in that 2. An S equipped with a SECAM signal discriminating circuit for discriminating whether or not an incoming signal is a SECAM signal.
In the ECAM signal processing circuit, a limiter amplifier that amplifies the SECAM signal and applies it to the SECAM signal discrimination circuit, and a level detection circuit that detects the level of the SECAM signal in the limiter amplifier are provided, and the detection output signal of the level detection circuit is provided. The SECAM signal discrimination circuit is adapted to switch the discrimination result according to the SECAM signal discrimination circuit.
Signal processing circuit.