JPH0752933B2 - Television receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to a television receiver capable of receiving television broadcasts of different systems.

2. Description of the Related Art A conventional example of a television receiver capable of receiving two types of television broadcasts having different audio intermediate frequencies (SIF) is shown in FIG.
It is shown in FIG. In Fig. 3, 1 indicates 4.5MHz or 5.5MHz
SIF circuit, 2 is a detection transformer of 4.5MHz or 5.5MHz,
3 is a 4.5MHz or 5.5MHz filter circuit, 4 is 4.5M
It is a discrimination circuit of Hz or 5.5 MHz. Switching of the SIF circuit, the detection transformer, and the filter circuit is controlled by the output signal of the discrimination circuit 4.

FIG. 2 shows a conventional example of the 4.5 MHz and 5.5 MHz filter circuit 3 shown in FIG. 3, where X4 is a 5.5 MHz filter and X5 is
Is a 4.5MHz filter, and 5 is a filter X5 switch circuit.

Now, when the 5.5 MHz SIF signal is input, the 5.5 MHz signal is input to the SIF circuit 1 and the discrimination circuit 4 through the filter X4, and the discrimination circuit 4 detects this 5.5 MHz signal and the received signal is 5.5. When it is determined to be MHz, the SIF circuit 1, the detection transformer 2, and the filter circuit 3 are switched to the 5.5 MHz side to obtain a proper voice detection signal.

The problem to be solved by the invention is that the current discrimination circuit discriminates "5.5MHz" until the SIF input signal is input, and each circuit is 5.5M.
Switching to the Hz side. Now, when the signal of 4.5 MHz, that is, the signal of NTSC is received, the switch circuit 5 is in the open state, and the SIF signal is input to the determination circuit via X4. The SIF input is a detection output of a video intermediate frequency amplification circuit (hereinafter abbreviated as VIF), and includes various frequency components. Among them, NTSC color carrier 3.58MHz signal and 4.5
A beat of 920 KHz is generated in the MHz signal, this beat component is input to the determination circuit, and the determination circuit erroneously determines that the SIF signal is input. As a result, SIF circuit 1, detection transformer 2
Had a problem that it was switched to 5.5MHz and a correct voice detection signal could not be obtained.

The present invention solves such a problem and provides a television receiver capable of obtaining a correct audio detection signal.

Means for Solving the Problems In the television receiver of the present invention, the second filter circuit is provided with a chrominance carrier trap circuit so as to obtain a correct audio detection signal when the first SIF signal is received.

Action The television receiver of the present invention is provided with a trap circuit for the color carrier of the first SIF signal on the second filter side of the first and second filter circuits, and the SIF signal of the received signal (for example, 4.5 MHz) And the erroneous discrimination of the discrimination circuit by the beat signal (920Hz) by the color carrier wave (for example, 3.58MHz) is completely eliminated.

Example One example of the present invention will be described below. In Figure 1,
Filter circuit 3 is ceramic, filters X1 to X3
And a ceramic trap X3 and a switch circuit 5. If the NTSC signal is input while the television receiver is not receiving anything now, the discrimination circuit will be 5.5MHz.
Therefore, the switch circuit 5 is in the open state, the SIF signal passes through the 5.5 MHz ceramic filter X1 side, and at this time, the color carrier wave is removed by the 3.58 MHz trap X3. As a result, since nothing is input to the discrimination circuit, the discrimination circuit determines that the input signal is a signal other than 5.5 MHz, that is, 4.5 MHz. As a result, the SIF circuit 1 and the detection transformer 2 are switched to the 4.5 MHz side. Therefore, a correct voice detection output can be obtained.

EFFECTS OF THE INVENTION As described above, the television receiver of the present invention has the first SI
F (for example 4.5MHz), a second SIF (for example 5.5MHz) filter circuit of the first SIF side is provided on the second SIF side of the filter circuit, and the received SIF signal (for example 4.5MHz) It is possible to completely eliminate erroneous discrimination of the discrimination circuit due to the beat signal (for example, 920 Hz) due to the color carrier wave (for example, 3.58 MHz).

[Brief description of drawings]

FIG. 1 is a circuit diagram of a television receiver according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional example, and FIG. 3 is a conventional example.
It is a basic circuit diagram of a SIF circuit and a discrimination circuit. 1 ... 4.5MHz / 5.5MHz SIF circuit, 2 ... 4.5MHz / 5.5MHz
Detection transformer of 3 ... 4.5MHz / 5.5MHz filter circuit, 4 ... 4.5MHz / 5.5MHz discrimination circuit, 5 ... 4.5MHz filter switch circuit, X3 ... 3.58MHz trap circuit.

Claims (1)

[Claims] Claim: What is claimed is: 1. A television receiver capable of receiving television broadcasts of different systems, comprising a first filter circuit comprising a 5.5 MHz filter and a 3.58 MHz trap, and a second filter circuit comprising a 4.5 MHz filter connected to a switch circuit. SIF filter circuit connected in parallel with the filter circuit of, the discrimination circuit that outputs the discrimination signal by discriminating the output signal from the SIF filter circuit, the 4.5MHz transformer and 5.5MHz transformer by the discrimination signal And a SIF circuit to which a switchable detection transformer is connected. The discrimination signal is applied to a switching control signal input terminal of a switch circuit disposed in the second filter circuit, and a switching control signal of the detection transformer is applied. The discrimination signal is supplied and the SIF signal is automatically output according to the type of the input SIF signal.
The filter circuit and the detection transformer are configured to be switched, and when the switch circuit provided in the second filter circuit is in an open state, the SIF filter circuit has a SIF of 4.5 MHz.
Even when a signal is input, the 3.58MHz trap provided in the first filter circuit removes the 3.58MHz signal component contained in the input SIF signal, and the switch circuit operates at 920KH.
A television receiver characterized in that an audio detection signal is output according to an input SIF signal without malfunctioning with a z beat signal.