JPS6133756Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a color killer circuit for a television receiver.

In television receivers, the color killer circuit malfunctions due to noise mixed into the received signal when receiving a color broadcast given by a weak electric field or when receiving a black and white broadcast, causing the color killer circuit to malfunction. Broadcasts may become black and white, or color noise may appear on black and white broadcasts.

The present invention has been proposed in view of this point, and provides a color killer circuit that alleviates the influence of noise mixed into received signals.

The present invention will be explained below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, 1 is an input terminal for a video signal, which is connected to a bandpass filter 2 of a predetermined band and a bandpass filter 3 of a narrower band. 4
is a switch circuit whose contact A is connected to band pass filter 2, and contact B is connected to band pass filter 3.
It is connected to the. The switch circuit 4 is connected to the color demodulation circuit 7 and the killer signal via the color amplification circuit 5.
It is connected to the ACC circuit 6. Killer again
The killer detection voltage and ACC detection voltage sent from the ACC circuit 6 are both transmitted to the color amplification circuit 5 and the OR circuit 8.
It is beginning to be given to The OR circuit 8 is configured to control the switch circuit 4 based on its output.

Next, the operation will be explained. When a color broadcast is received in a strong electric field, the switch circuit 4 is connected to the contact A side. At this time, the video signal input to the terminal 1 passes through a bandpass filter 2 of a predetermined band to extract a carrier color signal, and this carrier color signal is applied to a color amplification circuit 5 via a switch circuit 4. The carrier color signal taken out from the color amplification circuit 5 is given to a color demodulation circuit 7, where it is demodulated into a color signal. Further, a part of the carrier color signal taken out from the color amplification circuit 5 is given to the killer/ACC circuit 6. The killer/ACC circuit 6 detects a burst signal from the carrier color signal. When a burst signal is not present at this time (i.e., a burst signal cannot be detected because a black-and-white broadcast is received or a color broadcast is received with a very weak electric field)
A killer detection voltage is extracted to control the operation of the band amplifier circuit and prevent color signals or color noise from appearing on the picture tube screen. Furthermore, an ACC detection voltage is extracted based on the level of the burst signal to control the gain of the input carrier color signal so that the level of the carrier color signal is approximately constant between each channel. Both of these detection voltages are given to the color amplification circuit 5, where the above-mentioned color killer control and
ACC control is performed. Both detection voltages are also applied to the OR circuit, and when the killer detection voltage is detected or when the ACC detection voltage is below a predetermined level, the switch circuit 4 is controlled to switch to the contact B side. That is, when receiving a black and white broadcast or when receiving a color broadcast in a weak electric field, the video signal input from the terminal 1 is connected to the color amplification circuit via the band pass filter 3 having a narrower band than the band pass filter 2. In other words, when a color broadcast is received in a weak electric field, a narrow-band bandpass filter is used to detect the carrier color signal, which causes more interference in the received signal than when a color broadcast is received in a strong electric field. This improves the noise removal function and increases the sensitivity for distinguishing between color broadcasts and black and white broadcasts.

As explained above, according to the present invention, the malfunction of the color killer circuit caused by noise mixed in the received signal can be alleviated, both when receiving color broadcasts in a weak electric field and when receiving black and white broadcasts. It is.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 2...First color signal filter, 3...Second color signal filter, 4...Switch circuit, 5...Color amplification circuit, 6...Killer/ACC detection circuit.

Claims (1)

[Claims for Utility Model Registration] A first color signal filter that extracts an input carrier color signal in a predetermined band; and a second color signal that extracts the input carrier color signal in a band narrower than the predetermined band. a filter, a color signal amplification circuit that selectively amplifies one of the carrier color signals taken out from the two color signal filters, and a burst signal of the carrier color signal taken out from the color signal amplification circuit; a killer/ACC detection circuit that extracts a killer detection voltage when no signal is present and extracts an ACC detection voltage indicating the level of the burst signal when a burst signal is present;
and a switch circuit that selects the carrier color signal taken out from the second color signal filter and supplies it to the color signal amplification circuit in response to detecting that the ACC detection voltage is below a predetermined level. A color killer circuit featuring