JP3588167B2 - TV receiver - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a TV receiver that mutes an audio signal when there is no video signal, and more particularly to a TV receiver that can easily perform a test for measuring characteristics such as S / N of an audio signal.
[0002]
[Prior art]
2. Description of the Related Art TV receivers that mute an audio signal when no video signal is present have appeared. This has the effect of preventing noise from being amplified and emitted when no video is displayed.
In particular, in the PAL system, there is an ID (identification) circuit that identifies the presence or absence of a video signal in the standard, so that muting can be easily performed by using the output signal of the ID circuit.
[0003]
FIG. 2 shows such a TV receiver. A VIF (video intermediate frequency) signal from an input terminal (1) is amplified and detected by a VIF circuit (2). From the inter-carrier type VIF circuit (2), an audio IF signal is generated together with video, and audio is applied to a SIF (audio intermediate frequency) circuit (3) via a filter or the like.
The SIF circuit (3) demodulates and amplifies the audio signal.
[0004]
The ID circuit (4) identifies the presence or absence of a video signal based on whether or not there is a horizontal synchronization signal included in the video signal in the output signal of the VIF circuit (2). If it is determined that there is a video signal, the mute to the SIF circuit (3) is not performed. Conversely, if it is determined that there is no video signal, mute to the SIF circuit (3) is performed.
By the way, in the IC manufacturing process, it is necessary to check whether each circuit inside the IC is functioning normally. Also in the circuit of FIG. 2, a test signal is applied to the VIF circuit (2) and the SIF circuit (3), and the output signal waveform is observed.
[0005]
FIG. 3 shows a test method for such a TV receiver. To prevent the mute from being applied to the SIF circuit (3), it is necessary to apply a signal also to the VIF circuit (2). Therefore, it is necessary to simultaneously apply the test signals from the test signal sources (SG) (5) and (6) to the VIF circuit (2) and the SIF circuit (3). Then, a test is performed by measuring each output signal with an oscilloscope (7) (8) or the like.
[0006]
[Problems to be solved by the invention]
However, the method of FIG. 3 requires two test signals to be applied at the same time, so that two SGs are required, resulting in a problem that the measurement cost is increased.
In addition, since the video signals are generated adjacent to each other when measuring the audio signal, they cause interference with each other, so that accurate measurement cannot be performed.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above-described problems, and includes a VIF circuit for amplifying and detecting a video IF signal, an SIF circuit for amplifying and detecting an audio component in an output signal of the VIF circuit, A mute for canceling the mute operation in response to a command from an IC tester, in a TV receiver comprising: an ID circuit for detecting that the video IF signal in the VIF circuit is in a non-signal state and muting the SIF circuit. By providing a release circuit, a test signal for video is not applied to the VIF circuit when a test signal is applied to the SIF circuit.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a TV receiver according to the present invention. (9) and (10) show transistors for muting an amplifier (11) in an SIF circuit (3) according to an output signal of an ID circuit (4). , (12) are IC testers for generating a release signal for releasing the mute operation to the SIF circuit (3), and (13) is a terminal to which the release signal from the IC tester (12) and the AFT dayfeet signal are applied. , (14) are AFT circuits, (15) is a transistor that is turned on only when the release signal is applied, and (16) is a mute release transistor.
[0009]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the above circumstances, and includes a VIF circuit for amplifying and detecting a video IF signal; A TV receiver including an ID circuit that detects that the video IF signal in the middle is in a no-signal state and mutes the SIF circuit;
When performing the test of the SIF circuit, a mute release circuit for releasing the mute operation is provided, and a video test signal is not used when a test signal is applied to the SIF circuit.
[0010]
The SIF signal from the terminal (17) of the SIF circuit (3) is subjected to FM demodulation by an FM demodulator (20) after its amplitude is limited by a limiter (19). The FM-demodulated audio signal is amplified by the amplifier (11) and led out to the output terminal (21).
At this time, the release signal from the IC tester (12) is not applied to the terminal (13), and only the AFT dayfeet signal is applied. The base voltage of the transistor (15) is set to, for example, 5V. The level of the AFT day-feet signal is set sufficiently lower than 5V. Then, the transistor (15) is kept off, and the AFT dayfeet signal is applied only to the AFT circuit (4). In this state, when the ID circuit (4) detects the absence of the synchronizing signal, it generates an "L" level signal and turns on the transistor (9). Then, the transistor (10) is turned on to apply an “L” level signal to the amplifier (11), thereby causing the amplifier (11) to perform a mute operation.
[0011]
Therefore, according to the apparatus shown in FIG. 1, it is possible to mute the audio signal when no video signal exists.
Note that when not muted, the transistors (9) and (10) are off.
Next, it is assumed that the TV receiver in FIG. 1 is in the middle of a manufacturing process and a circuit test is performed. In this case, the test signal source (6) is provided at the terminal (17) of the SIF circuit (3), but the SG is not provided at the terminal (1) of the VIF circuit (2). Therefore, there is no problem of interference between video and audio. Further, based on a command from the IC tester (12), a release signal for releasing the mute operation is applied to the terminal (13).
[0012]
Since no signal is applied to the terminal (1), the ID circuit (4) applies an "L" level signal to the base of the transistor (9) for muting by determining that there is no signal. Then, as described above, the transistor (10) tries to turn on. However, when the release signal of 5 V or more is applied to the transistor (15), the transistor (15) turns on and the transistor (16) turns on. . Then, the transistor (10) is forcibly turned off, and the amplifier (11) is not muted.
[0013]
Therefore, the test signal from the terminal (17) normally passes through the SIF circuit (3) and is led out to the output terminal (21), so that an accurate test can be performed.
[0014]
【The invention's effect】
As described above, according to the present invention, the test of the SIF circuit can be easily performed even in a TV receiver provided with an ID circuit and automatically muted.
In particular, according to the present invention, since only one SG is required, there is an effect that accurate measurement and cost are not required.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a TV receiver according to the present invention.
FIG. 2 is a circuit diagram showing a conventional TV receiver.
FIG. 3 is a diagram for use in a method of measuring the TV receiver of FIG. 2;
[Explanation of symbols]
(2) VIF circuit (3) SIF circuit (4) ID circuit (16) Transistor

Claims (1)

A VIF circuit for amplifying and detecting the video IF signal;
An SIF circuit for amplifying and detecting an audio component in an output signal of the VIF circuit;
A mute for canceling the mute operation in response to a command from an IC tester, in a TV receiver comprising: an ID circuit for detecting that the video IF signal in the VIF circuit is in a non-signal state and muting the SIF circuit. when applying a test signal to the SIF circuit by Rukoto provided release circuit, TV receiver, characterized in that not applying a test signal for the video to the VIF circuit.

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