JPH04252671A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To obtain the noise reduction circuit used for a multi-system corresponding multi-television set by a simple constitution by switching a constant of an element for determining a resonance frequency of a resonance circuit by a switching circuit. CONSTITUTION:When a PAL and SECAM corresponding input signal is inputted to a switching input terminal 15 of a resonance circuit frequency changeover switching circuit 3, and the terminal 15 becomes HI, a transistor 18 is turned on a coil 26 of a pi type resonance circuit 4 which is set so as to resonate to a color subcarrier frequency is bypassed, and a resonance frequency becomes high. Also, in the case of an NTSC corresponding input signal, the terminal 15 is L0W, the transistor 18 is turned off and the coil 26 is not bypassed, and the resonance frequency becomes low. Accordingly, a television detects each received system by another circuit not shown in the figure, and by inputting a signal to the terminal according to its result, the resonance frequency can be allowed automatically to conform to its system.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction circuit that operates in accordance with various television systems.

0002

2. Description of the Related Art In recent years, due to the demand for higher picture quality in televisions, the so-called Y-C separation method is increasingly being adopted. At this time, if the chroma (C) signal leaks into the luminance (Y) signal, noise such as dot interference will occur, so it is removed using a noise reduction circuit. A conventional noise reduction circuit introduced into the NTSC system has already been announced, but the future challenge is to introduce it into a multi-set compatible with multiple systems such as PAL and SECAM.

0003

[Problem to be solved by the invention] However, since the color subcarrier frequency is different for each system, conventional circuits can only operate in the NTSC system, but cannot be applied to other systems as they are because the circuit constants must be changed. I couldn't do it.

[0004] The present invention has a simple configuration and can be used with NTSC or PA.
The present invention aims to provide a noise reduction circuit used in a multi-system compatible multi-television set that supports each of the L and SECAM systems.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the noise reduction circuit of the present invention includes a resonant circuit provided between a video signal source and an output terminal, and a resonant circuit that is activated or short-circuited. Noise reduction O to switch
A resonant circuit frequency switching circuit having an N/OFF circuit and a switching input terminal for inputting a system compatible input signal whose level has changed in accordance with a plurality of television systems, and determines the resonant frequency of the resonant circuit. The constant of the element is switched by the resonant circuit frequency switching circuit.

[0006]

[Operation] According to the above-described configuration, the present invention switches the constant of the element that determines the resonant frequency of the resonant circuit by the resonant circuit frequency switching switching circuit, thereby changing the resonant frequency of the resonant circuit to a different color subcarrier frequency for each method. It is possible to remove the chroma signal leaked into the luminance signal and perform noise reduction operations compatible with multiple methods.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to FIG. 1, which is a block diagram of a noise reduction circuit according to an embodiment of the present invention. A video signal source 1 is input to a noise reduction ON/OFF circuit 2. Noise reduction ON/OFF
In circuit 2, switch 1 is placed on the front of the set.
One end of 0 is connected to a resistor 11 connected to the power supply +B, the other end is connected to the base of a transistor 14 via a resistor 12, and from that connection point, a resistor 13 is connected to a connection point between the emitter of the transistor 14 and the video signal source 1. It is connected.

Resonant circuit frequency switching switching circuit 3
is for switching the resonant frequency of the π-type resonant circuit 4, which will be described later, according to each of the NTSC, PAL, and SECAM systems, and is a switching input terminal for inputting a system-compatible input signal corresponding to each of the NTSC, PAL, and SECAM systems. 15 is connected to the base of a transistor 18 via a resistor 16, and the connection point thereof is grounded through a resistor 17. The noise reduction ON/OFF circuit 2 inputs NTSC or PAL and SECAM to the switching input terminal 15.
Operates with priority over compatible input signals.

In the π-type resonant circuit 4, resistors 19, 20, and 23 are connected in series between the emitter of the transistor 14 of the noise reduction ON/OFF circuit 2 and the output terminal 27. Capacitors 21 and 22 are connected from the connection points of the two capacitors, and the other ends of these two capacitors are connected, and the coils 25 and 26 are connected via a resistor 24.
It is grounded through.

The structure is constructed as described above, and its operation will now be explained. When the switch 10 is closed, the transistor 14
is forward biased and turned ON, the signal of the video signal source 1 bypasses the noise reduction ON/OFF circuit 2 and is output to the output terminal 27, and the noise reduction is turned OFF.

Next, when the switch 10 is turned off, the transistor 14 is turned off with no bias, and the signal from the video signal source 1 passes through the π-type resonant circuit 4 without going through the transistor 14 and is output to the output terminal 27. Ru. At this time, when the PAL and SECAM compatible input signals are input to the switching input terminal 15 and the terminal 15 becomes HI, the transistor 18 is turned on and the coil 26 of the π-type resonant circuit 4 is turned on.
bypass, and the resonant frequency becomes higher. In the case of an NTSC compatible input signal, the terminal 15 is LOW, the transistor 18 is turned off, the coil 26 is not bypassed, and the resonant frequency becomes low. This π-type resonant circuit 4 is set to resonate with the color subcarrier frequency, and for example, the coil 2
When 5 and coil 26 are connected in series, it is 3.58M in NTSC system.
Hz, 4.43M of PAL system when only coil 25 is used.
Hz, SECAM method 4.25MHz and 4.40
It is designed to resonate in the middle of 625MHz. Therefore, the television detects each received system using another circuit (not shown) that detects each system, and based on the result, inputs a signal to the switching input terminal 15 to automatically adapt the resonance frequency to that system. Can be done.

Although a π-type resonant circuit is used here as the resonant circuit, other resonant circuits or filter circuits may also be used, and the constant of the element that determines the resonant frequency or the stopping frequency is set as the resonant circuit. It is sufficient to switch the frequency using the frequency switching circuit 3.

[0013]

As explained above, according to the present invention, it is possible to remove noise from a luminance signal in a television set compatible with multiple systems such as NTSC, PAL, and SECAM with a simple circuit configuration, thereby eliminating noise such as dot interference. It is possible to provide a practically useful means of mitigating this.

[Brief explanation of the drawing]

[Fig. 1] Block diagram of a noise reduction circuit according to an embodiment of the present invention.

[Explanation of symbols]

1 Video signal source 2 Noise reduction ON/OFF circuit 3 Resonant circuit frequency switching switching circuit 4 π-type resonant circuit (resonant circuit) 15 Switching input terminal 27 Output terminal

Claims (1)

[Claims] 1. A resonant circuit provided between a video signal source and an output terminal, a noise reduction ON/OFF circuit for switching the resonant circuit to an operating state or a short-circuited state, and a level control circuit for adjusting a level corresponding to a plurality of television systems. a resonant circuit frequency switching switching circuit having a switching input terminal for inputting a changed system compatible input signal, and configured to switch a constant of an element that determines the resonant frequency of the resonant circuit by the resonant circuit frequency switching switching circuit. noise reduction circuit.