JPS595795A - Color killer circuit - Google Patents

Abstract

PURPOSE:To perform secure operation without the influence of a 4.5MHz sound carrier signal, by operating either of subcarrier oscillating circuits selectively on the basis of both combined outputs, i.e. the output of a multioscillating circuit whose oscillating operation is brought under on-off control according to whether a killer detection output is present or not and the output of a sound discriminating circuit which discriminates a sound carrier frequency. CONSTITUTION:The sound discriminating circuit 9 which discriminates between the carrier frequencies of a 4.5MHz and a 5.5MHz sound IF signal is provided together with an OR gate 10, and the oscillating operations of two subcarrier oscillating circuits 6 and 7 are switched on the basis of the mixed output of the oscillation output of an astable multioscillating circuit 8 and the discrimination output of the sound discriminating circuit 9. When a color television signal is received, a 3.5MHz subcarrier signal separated by a burst gate circuit 3 and a 3.58 subcarrier signal obtained by the subcarrier oscillating circuit 6 are supplied to a killer detection circuit 4 for killer detection and the oscillating operation of the astable multioscillating circuit 8 is stopped on the basis of the killer detection output obtained at this time. On the other hand, when a black-and-white television signal is received, no killer detection output is sent out of the circuit 4 even if a 4.5MHz sound carrier signal is outputted from the burst gate circuit 3 erroneously and supplied to the circuit 4 because the circuit 6 is in normal oscillating operation at this time, and consequently the amplifying operation of the 2nd band amplifier 2 is stopped to perform normal color killer operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color killer circuit suitable for implementation in a VTR (video tape recorder) monitor receiver and a color television receiver which can also be used in a color television receiver.

Currently, especially in export-oriented VTRs, when recording NTSC color television signals, a frequency different from that of the NTSC standard system may be used for recording, taking into consideration the actual state of color television broadcasting in the destination country. For example, as shown in Table 1, in some cases (tentatively called the NTSC-1 system), the subcarrier frequency of the chroma signal remains unchanged (3.58 M
Hz) and uses 5.5 MHz as the audio carrier frequency, and in some cases (tentatively called the NTSC-2 system) uses 4.43 MHz as the subcarrier frequency of the chroma signal and uses 5.5 MHz as the audio carrier frequency. MHz is used.

Table 1 Therefore, in such a case, it is necessary to receive not only the normal NTSC standard color television broadcast, but also the NTSC-L standard system.
There is a need for a color television receiver that can also receive reproduced images from VTR tapes recorded in the NTSC-1 and NTSC-2 formats.

Therefore, a receiver that satisfies this type of request has been developed and is already being exported.

Figure 1 shows an example of a color killer circuit used in a conventional color television receiver (keyaki).The operation of this circuit will be explained.In Figure 1, 1 is a band amplifier, 2
is the second band amplifier, 3 is the burst gate circuit, 4 is the killer n-wave circuit, 5-digit killer amplifier, 6 is the 3.58MHz subcarrier oscillator, 7 is the 4.43MHz subcarrier oscillator, and 8 is the astable multi-oscillation. In this astable multi-oscillation circuit 8, the oscillation operation is controlled on/off depending on the presence or absence of the killer output of the killer amplifier 5, and the two subcarrier oscillation circuits 6 and 7 control the oscillation output of the multi-oscillation circuit 8. Based on this, only one of -)j always performs an oscillating operation, and the other one is stopped from oscillating. The amplification operation of the second band amplifier 2 is controlled on/off depending on the presence or absence of the killer output of the killer amplifier 5.

When a color television broadcast of the NTSC standard format is received here, a composite video signal is supplied to the first band amplifier 1, and here, the 3.58 MHz in particular of the composite video signal is supplied to the first band amplifier 1.
Only the chroma signal component of is selectively amplified, and this chroma signal is supplied to the second band amplifier 2 and the burst gate circuit 3, respectively. At this time, the burst gate circuit 3 separates and derives only the burst signal from the chroma signal based on the gate pulse, and supplies this to the killer detection circuit 4. On the other hand, during this steady state, the astable multi-oscillator circuit 80 oscillation operation is stopped, and the output of this oscillation circuit 8 is, for example, ゛H゛°
At this time, the 3.58 MHz subcarrier oscillation circuit 6 performs oscillation operation, and the other oscillation circuit 7 is stopped. Therefore, at this time, the 3.58 MHz subcarrier signal is supplied to the killer detection circuit 4, where killer detection is performed together with the burst signal. The killer detection output, which cannot be obtained at this time, is amplified by the killer amplifier 5 and then supplied to the second band amplifier 2 and the astable multi-oscillator circuit 8. When this killer detection output is present, the second band amplifier 2 performs a j-stationary amplification operation, and at this time, the chroma signal obtained from the first band amplifier 1 is further amplified and derived.

On the other hand, at this time, the oscillation operation is stopped in the astable multi-oscillation circuit 8, and the output of this oscillation circuit 8 is always at the "H" level, thereby maintaining the oscillation operation of the 3.58 MHz subcarrier oscillation circuit 6. Strengthen.

When receiving this standard color television signal, for some reason the output of the astable multi-oscillator circuit 8 becomes "L゛°°".
If the 4.43 MHz subcarrier oscillation circuit 7 starts oscillating even temporarily due to this, the killer detection output from the killer detection circuit 4 disappears.
The operation of the astable multi-oscillator circuit 8 is immediately reversed, and as a result, the output of the oscillation circuit 8 becomes "H" level again, and after that, the 3.58 MHz subcarrier oscillator circuit 60 oscillates again, returning to a steady operating state. be returned.

Furthermore, when receiving a color television signal of the NTSC-1 system during VTR playback, etc., the subcarrier frequency in the chroma signal obtained from the first band amplifier 1 is 3.58 MHz, which is the same as the above-mentioned NTSC standard system. Exactly the same operation as described above is performed, that is, at this time, the second band amplifier 2 performs the normal chroma signal amplification operation, and the oscillation operation of the 3.58 MHz subcarrier oscillation circuit 6 is performed constantly.

On the other hand, when receiving an NTSC-2 color television signal during VTR playback, etc., the first band amplifier 1
．． A 43 MHz chroma signal is derived and supplied to the burst gate circuit 3.

At this time, the burst gate circuit 3 generates a gate pulse of 4.43. The MHz burst signal is separated and derived and supplied to the killer detection circuit 4. On the other hand, in this case, the output of the astable multi-oscillator circuit 8 becomes "L" level, and the output becomes 4.43.
While the 70 MHz subcarrier oscillation circuit is operating, a killer detection output is derived from the killer detection circuit 4, and based on this, the second band amplifier 2 performs a chroma signal amplification operation. In the stable multi-oscillation circuit 8, the oscillation operation is stopped 1. when the output is at the "L°" level, so that the oscillation operation of the 4.43 MHz subcarrier oscillation circuit 7 is maintained.

Next, when receiving the switched black-and-white television signal, the killer detection output of the killer detection circuit 4 is not derived unless there is a burst signal component, and at this time, the astable multi-oscillator circuit 8 performs an oscillation operation at a constant period. The action is reversed. Therefore, at this time, the two subcarrier oscillation circuits 6.7 alternately oscillate, and subcarrier signals of 358 MHz and 4.43 MHz are sequentially supplied to the killer detection circuit 4. However, in this case, since no burst signal is derived from the burst gate circuit 3, the killer detection output of the killer detection circuit 4 is usually not derived, and as a result, the amplification operation is stopped in the second band amplifier 2, so-called color killer operation. will be carried out.

In this way, in the conventional color killer circuit shown in Fig. 1, a color killer operation is performed when receiving a black and white television signal, but in such a conventional circuit, when receiving a black and white television signal in the standard system, the first band amplifier 1, a 4.5 MHz audio carrier signal may be mixed into the burst gate circuit 3, and this is supplied to the killer detection circuit 4, while the subcarrier oscillation circuit 7
．． When a 43 MHz subcarrier signal is supplied to the killer detection circuit 4, the killer detection circuit 4 will erroneously derive a killer detection output because the frequencies of the two signal signals are very close to each other, resulting in unstability. The 80-oscillation operation of the multi-oscillator circuit is stopped and the output becomes "L゛° level," and at this time the 4
．． The 43 MHz subcarrier oscillation circuit 7 is always oscillated. At the same time, the @2-bandwidth amplifier 2 performs an amplification operation based on the killer detection output, but at this time, the power amplifier operation is not performed, and as a result, there is a possibility that color noise may occur on the screen.

The present invention has been made in view of the drawbacks of the conventional circuits, and it is an object of the present invention to provide a color killer circuit that operates reliably without being affected by a 4.5 MHz audio carrier signal.

A description will be given below along with one embodiment of the present invention shown in FIG.

In Fig. 2, parts that are the same as those in the conventional circuit in Fig. 1 are given the same reference numerals1. Voice discriminator circuit 9 and or game) 10
is added to L1, and the oscillation operation of the two subcarrier oscillation circuits 67 is switched and controlled by the outputs of both the oscillation outputs of the astable multi-oscillation circuit 8 and the discrimination outputs of the voice discrimination circuit 9. This is what I did.

That is, in this case, when receiving an NTSC standard television signal, the audio IF signal is 4.5 MHz regardless of whether the content is color television broadcasting or black and white television broadcasting.
The audio carrier wave signal is supplied to the audio discrimination circuit 9, and at this time, an output of "H" level is always derived from the discrimination circuit 9 as a discrimination output.

Since this is supplied to both subcarrier oscillation circuits 6.7 via OAGOO 1-1Off, in this case it is always 3.58M regardless of the output of the astable multi-oscillation circuit 8.
The Hz sub-carrier oscillation circuit 6 is operated to oscillate.

Therefore, especially when receiving a color television signal, the 3.58 MHz burst signal separated by the burst gate circuit 3 and the 3.58 MHz The subcarrier signal is subjected to killer detection in the killer detection circuit 4, and based on the killer detection output obtained at this time, the second band amplifier 2 performs a normal chroma signal amplification operation, and the astable multi-oscillator circuit 8 The oscillation operation is stopped.

However, even if a 4.5 MHz audio carrier signal is erroneously derived from the burst gate circuit 3 when receiving a monochrome television signal and is supplied to the killer detection circuit 4, the 3.58 MHz subcarrier signal is Since the oscillation circuit 6 is always in oscillation operation, a killer detection output is not derived from the killer detection circuit 4. Therefore, in this case, the second band amplifier 2 stops its amplification operation and performs a normal color killer operation.

On the other hand, when receiving a black-and-white television signal in the NTSC-1 system or NTSC-2 system, the discrimination output of the audio discrimination circuit 9 is "L'00", so the two subcarrier oscillation circuits 6 and 7 are connected to the astable multi-oscillation circuit 8. Based on the oscillation output of the burst gate circuit 3, the oscillation is performed alternately at a constant period.
Even if a 5°5 MHz audio carrier signal is derived by dei, the killer detection output of the killer detection circuit 4 is not derived at all, and therefore, the second band amplifier 2 performs a regular color killer operation. .

Furthermore, when receiving a color television signal in the NTSC-1 system or NTSC-2 system, one of the subcarrier oscillation circuits 6.7 is operated in oscillation based on the output of the astable multi-oscillation circuit 8, and this oscillation output and burst The burst signal of 3, 58 MHz or 4.43 MHz obtained from the gate circuit 3 is subjected to killer detection, and the second band amplifier 2 performs normal amplification operation based on the killer detection output obtained at this time. During the stable multi-oscillation interval '#S8, the oscillation operation is stopped at a predetermined output state.

As described above, the color killer circuit of the present invention has two subcarrier oscillation circuits that oscillate different subcarrier frequency signals, and the subcarrier signal and chroma signal obtained from either subcarrier circuit are The amplification operation of the band layer $M device is controlled on and off based on the presence or absence of a killer detection output obtained by detecting the color subcarrier signal, and the oscillation operation is turned on or off depending on the presence or absence of the killer detection output. Either one of the carrier wave oscillation circuits on both sides is selectively operated based on the combined output of not only the output of the controlled multi-oscillation circuit but also the output of a voice discrimination circuit that discriminates the voice carrier frequency. Therefore, even if the chroma signal is mixed with an audio carrier signal close to one of the subcarrier frequencies, the killer detection output is accurately derived only when receiving a color TV signal, and the signal is not detected when receiving a monochrome TV signal. No pseudo detection output is derived, and in this case, no color killer operation is performed erroneously.

Can be used as a color killer circuit.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional color killer circuit, pR
FIG. 2 is a block diagram of one embodiment of the present invention. 2... Second band multiplier, 3... Burst gate circuit, 4... Killer detection' circuit, 5... Killer amplifier,
6...3.58MHz subcarrier oscillation circuit, 7 ・4.
43 MHz subcarrier oscillation circuit, 8... Astable multi-oscillation circuit, 9-4.5 MHz 15.5 MHz
? Near voice discrimination circuit.

Claims (1)

[Claims] 1 In a color killer circuit in which the operation of a band amplifier is controlled on/off based on the presence or absence of a killer detection output obtained by detecting a subcarrier oscillation signal and a color subcarrier signal in a chroma signal, the presence or absence of the killer detection output a multi-oscillation means whose oscillation operation is controlled on and off according to the frequency, an audio discrimination means that discriminates the carrier frequency of the audio intermediate frequency signal, and two subcarrier oscillation means that appropriately oscillate subcarrier signals of different frequencies. , oscillation control means for selectively operating one of the side carrier wave oscillation means based on the output of both the oscillation output of the multi-oscillation means and the discrimination output of the voice discrimination means. circuit.