JPH03106230A - Television receiver - Google Patents

Abstract

PURPOSE:To offer the best video image to the user hy constituting an automatic video image noise reduction circuit utilizing a control voltage to a tuner of an AGC circuit. CONSTITUTION:A voltage in response to an input electric field strength to an antenna 1 is outputted from an automatic gain control circuit(AGC) 2 to a terminal TP 15 and when an input signal to the antenna 1 is weak and noise starts appearing on the screen of a television receiver, the highest voltage is applied to a high frequency amplifier circuit 3a of a tuner 3 and the tuner 3 acts at a highest gain. When the input signal is stronger, the output voltage from the AGC circuit 2 is decreased to decrease the gain of the tuner 3. Thus, the gain of the high frequency amplifier circuit 3a of the tuner 3 is controlled by an AGC output voltage to keep the input signal level to an intermediate frequency amplifier circuit 4 nearly constant. Thus, the best video image is observed.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a television receiver that detects the strength of an input signal to an antenna and uses this to remove image noise when the input signal is weak. be. BACKGROUND OF THE INVENTION Several conventional video noise reduction circuits have already been put into practical use. This is to make noise less noticeable when the electric field is weak.

By the way, it is currently up to the user to decide whether or not to operate this circuit. Problems to be Solved by the Invention Therefore, there are many cases where the video noise reduction circuit is operated when the input signal to the antenna is strong.
On the contrary, this leads to the screen losing its sharpness when the input signal is good.

In view of the above-mentioned problems, the present invention has been devised so that the video noise reduction circuit does not operate when the input signal is good, and the circuit operates or does not operate depending on the input signal strength, so that the circuit operates only when the signal is weak and actually produces an effect on the screen. By controlling the
It always tries to present the best images to the user.

Means for Solving the Problems In order to achieve this object, the television receiver of the present invention has an automatic amplification gain control mT! l pressure (hereinafter referred to as AG
It attempts to control the video noise reduction circuit by using changes in the AGC voltage in response to changes in the strength of the input signal to the tuner. As a result of this, the video noise reduction circuit operates only when the input signal to the antenna is weak and there is a lot of noise on the screen, and does not operate when the signal is good, and the sharpness of the screen is not lost. In addition, users can always see the best image without having to judge whether or not to activate the circuit. EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the circuit structure of a television receiver according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram thereof. In FIG.
When the human input signal to the antenna L is weak and noise begins to appear on the screen of the television receiver, the highest voltage value (approximately 8V) is output from the tuner 3 (referred to as the C circuit).
is applied to the high frequency amplifier circuit 3a, and the tuner 3 operates at maximum gain. Also, as the input signal becomes stronger, the AGC
The output voltage from circuit 2 decreases, working to lower the gain of tuner 3. In this way, the gain of the high frequency amplifier circuit 3a of the tuner 3 is controlled by the AGC output voltage, and the level of the input signal to the intermediate frequency amplifier circuit 4 is kept almost constant. Figure 2 shows the relationship between the electric field strength input to the antenna and the voltage at terminal TP15 in a reverse type AGC circuit.Using this characteristic, video noise is suppressed only when the input signal to antenna 1 is weak and noise appears on the screen. The circuit that operates the reduction circuit 5 is the circuit shown in Figure 1. In FIG. 1, transistor Q1 has a pull-up resistor R
2 forms a switch circuit, and the signal switching electronic switch Sl, 32 is controlled depending on whether the collector potential is LOW or HIGH. Furthermore, the diode D1 and the Zener diode D2 determine the operating voltage of the transistor Ql, and the voltage higher than the sum of the Vlffi voltage of the transistor Q1, the Zener voltage of the Zener diode D2, and the ON voltage of the diode D1 is the voltage that the diode D1 has. When applied to the anode, transistor Q1 is turned on. Here, the Zener voltage of the diode D2 is set to 6V, which is said to have good temperature characteristics, and the diode D1 is turned ON! ■. of voltage and transistor Q1. Assuming that 0.6V, the transistor Ql will turn on if a voltage of 7.2V or more is applied to the anode of the diode D1. On the other hand, as shown in Figure 2, the relationship between the input electric field strength to the television receiver and the output voltage of the AGC circuit 2 rises sharply just before the screen becomes noisy, and when the screen becomes noisy, it becomes 8■. Therefore, the transistor Q1 is sufficiently ONL, and the switches Sl and S2 are turned ON so that the video noise reduction circuit 5 operates, thereby attenuating the noise on the screen. As described above, the operation of the video noise reduction circuit 5 can be controlled by the input electric field strength. The resistor R1 is used to reduce the influence of the switch circuit mainly composed of the transistor Ql on the AGC control of the tuner 3. Further, in FIG. 1, 3b is a local oscillation circuit, 3c is a mixing circuit, 6 is a video detection circuit, and 7 is a local oscillation circuit.
, 8 are LPF and HPF for noise removal. As described above, the present invention provides control over the tuner of the AGC circuit.
! By using an automatic video noise reduction circuit that utilizes pressure, it presents the user with the best possible video, and its practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a television receiver according to an embodiment of the present invention, and a characteristic diagram of the second AGC circuit.

Claims (1)

[Claims] A detection means for detecting the strength of the input signal to the antenna, a video noise reduction circuit for reducing or removing noise components in the video signal, and an upper detection means for indicating that the level of the input signal has become lower than a predetermined value. and control means for operating the video noise reduction circuit based on the detection output of the television receiver.