JPS583486A - Band adjusting circuit for video signal - Google Patents

Abstract

PURPOSE:To prevent an interference signal from introduction to a chroma signal circuit, by providing a trap circuit which has a tuning frequency in the frequency range of a video carrier of upper adjacent channel and an audio carrier of reception channel. CONSTITUTION:An audio trap circuit 6 is connected to an output terminal T2 of an intermediate frequency amplifying circuit 4. The audio trap circuit 6 is connected to a video amplifier circuit 5 via a trap 10. The resonance frequency of the trap circuit 10 is selected to a frequency almost a half the frequency of the audio carrier and the video carrier of upper adjacent channel to set so that the frequency band from the audio carrier frequency to the frequency of the video carrier of upper adjacent channel can be attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention adjusts the band of the detection output of the video signal to prevent interference signals from entering the color 4Ii circuit, etc.

The present invention relates to a video signal band adjustment circuit.

One channel of a television signal is divided at a certain frequency, and the frequency bands of each channel are determined so that they do not overlap. - As an example, the frequency spectrum of an NTSC television signal is as shown in Figure 1. Each channel occupies a fixed band (@MHs), within which the video carrier P, the audio carrier, and the color subcarrier C. The number of cycles is determined, and the audio carrier wave 8 and the color carrier liquid C are 4 and 3, respectively, for the eirin carrier eK.
．． 88 (MHs), and these television signals are generally divided into two types: video carrier P, audio carrier, and 5KL is provided to prevent interference with the carrier wave 8 and the color subcarrier C. FIG. Band adjustment circuit 1. This is a series transmission line between an intermediate frequency signal amplification line 4 which is made up of an amplifier 2 and one detection circuit 3 and which are connected in series, and an Eirin amplification circuit 5. In this figure, the detection circuit 3 extracts the i number of both the Eirin carrier wave and the audio carrier wave, and a part of this detection output is supplied to the audio intermediate frequency circuit, and a part is supplied to the Eirin circuit SK audio. The signal is amplified via the trap circuit 6. The frequency characteristics of the intermediate frequency amplification circuit 40 shown in FIG. 2A are as shown in FIG. 2A. FIG. 3a is a frequency characteristic diagram of the intermediate frequency signal amplifying circuit 40 in which the vertical axis represents attenuation and the horizontal axis represents frequency, which is mainly determined by the band adjustment circuit 1. 31st
Trap frequencies /,U,/ on both left and right sides of the figure. represent the video carrier of the upper adjacent channel and the audio carrier of the lower adjacent channel, respectively, and within these frequency bands, the video carrier /P and the audio carrier f8 of the falling channel (n is an integer)
and can be adjusted to predetermined characteristics. Audio carrier wave/1! is the beat with color subcarrier I 20
(KHz) frequency, the attenuation amount is greater than that of the video carrier wave /P. The audio carrier wave of the detection output of the detection circuit 3 whose band has been adjusted in this way is trapped in the Eirin amplifier circuit i, and only the Eirin signal is supplied to the color signal circuit (not shown). is supplied to the picture tube without producing any beats.

Further, FIG. 2b is a block diagram showing a so-called separate carrier type intermediate frequency signal amplification circuit in which two detection circuits are provided in the intermediate frequency amplification circuit 4. In this figure [
In order to extract the Eirin signal and the audio signal, the output of the amplifier 2 is supplied to the audio intermediate frequency circuit via the first detection circuit 7, and the audio signal is connected between the amplifier 2 and the second detection circuit 8. The structure is such that a carrier wave trap aA is installed.

In this way, a trap circuit 9' is installed before the detection of the intermediate frequency amplification circuit 4.

The frequency characteristics of the inter-frequency amplification circuit 40 are shown in Figure 3b.

As the sound carrier wave /8 and the frequencies below it become less like the characteristics shown in Fig. 3a, the amount of attenuation increases even more.
Interference with the frequency of the above-mentioned Isshiki subcarrier can be more effectively suppressed. However, in the characteristics shown in Fig. 311, the bounce width of the lower frequency band of the audio carrier f8 is larger than that of Fig. 3a ≠ the audio carrier due to fluctuations in the local oscillation frequency of Yuner! Since the amplitude change of , becomes large,
There is also an intermediate control signal amplification circuit which prevents the occurrence of a bounced part of the audio carrier wave f8 as shown in the characteristics shown in FIG.

With these characteristics, and the circuit configuration! When the difficult-to-figure detection circuit uses an intermediate frequency signal amplification circuit with one method, for example, if the local oscillation frequency of CH-100 shifts to a lower direction, the level of the audio carrier wave /8 becomes extremely small and the audio- There is a risk that the operation of the road system may become unstable.

In addition, if we focus on the video carrier wave/PI of the upper channel and the audio carrier wave of the lower channel, the frequency band assigned to one channel of the television signal is determined by the above-mentioned formula, Tayo-6 (MH, i). 5. For example, there are cases where the same channel is broadcast with shifted video carrier detection due to regional differences.1 This means that the above-mentioned allocated band is above or below the channel. Depending on the selection equipment characteristics of the above-mentioned video channel and allocated bandwidth, the video carrier of the upper channel and the audio carrier of the lower channel may be mixed in. Yes, the above-mentioned divinity is better if it is as steep as possible.

These parts are used in modern C/V systems when transmitting television signals through a cable to a television screen, like a stem. It's a small cable TV show! I believe! A 7-year-old vision receiver suffers from interference with the F9 signal and the television signal propagating through the air? Interference occurs. .

In order to suppress this interference, the frequency interference of the current carrier wave, which is referred to as the 7-set, is removed in the same way as described above.

This offset means that the energy of the video carrier wave P is stronger in the band below that of the color printing carrier wave S, and as shown in FIG. The difference in carrier wave P between
Hz], and the sound carrier wave S of the nth channel is
K so that it overlaps with a part of the video carrier wave P of channel n+1). If the a-th channel kK offset is applied on top of this, it will be influenced by the video carrier P of the (n+1')-th channel. Therefore, if the third channel is received, the output of the intermediate frequency amplification stage of the television or vision receiver will include the video carrier wave of the (n+1)th channel in addition to the video signal, audio signal, and carrier color signal of the nth channel. A signal due to p2 also appears and becomes an interference signal. In this case, the frequency of the interference signal at the output of the intermediate frequency amplification stage is 5 (MHs), and the frequency band of the video signal amplification system after the intermediate frequency amplification stage is generally l.
Since it is set to a narrow band of approximately S (MHI), it does not appear in a monochrome picture tube, but in a color picture tube with a color signal circuit, the frequency of the interference signal b [M
H snow] and the color subcarrier (s, 58 (
Mlhl) causes a beat, resulting in a color shift phenomenon. Moreover, the frequency of this interference signal is not constant between each channel, but is allowed to be set over a relatively wide frequency range.
(MHz) ) ill Za figure and hitlL2kll
Depending on the conventional intermediate frequency signal amplification circuit that traps the signal before the junction with the audio circuit system as shown in K, the upper I
It was also difficult to completely eliminate the video transmission &/, of the police channel, and the audio microtransmission wave/jlD of the lower adjacent channel.

The present invention has been made in view of the above-mentioned points, and includes providing a trap enclosure or a low pass filter for removing the audio carrier wave of the upper adjacent channel and the audio carrier wave of the lower adjacent channel at the front stage of the audio amplifier circuit. Accordingly, an object of the present invention is to provide a video signal band 1+ circuit that prevents interference caused by a signal of a channel below a channel offset to be narrower than a standard frequency allocation width between channels.

The present invention will be explained below based on the following. FIG. 5 is a circuit diagram showing an embodiment of the present invention, and FIG. 6 shows the frequency-temporal characteristics of the trap circuit, which is the main component thereof. First, the configuration of FIG. 5 and 9 will be described. Elements that are the same as those of the conventional example are denoted by the same reference numerals, and a description of the configuration will be omitted.

The configuration of the intermediate frequency amplification circuit 4 is such that the video signal and the audio signal are passed through the same detection tlL- path and then sent to the respective single path systems. Therefore, to the output terminal i of this intermediate frequency amplification circuit 4, a composite image signal is outputted by combining the video carrier wave IP1 color subcarrier /C and the audio carrier wave /8 output from the detection circuit 3, and this terminal T , are connected to the audio trap circuit 6wc. The configuration of the audio trap circuit 6 is such that the common terminal of a three-terminal surface acoustic wave (hereinafter referred to as 8y) filter 61 is grounded, and an inductance 62 is connected between the two terminals divided into two electrodes via a thread pendulum. . This audio trap enclosure 6 is 4.5 (MH
This zero-order audio trap circuit 6, which traps the audio carrier wave of s), is connected to the video amplifier circuit 611C via the trap circuit io, which is the main part of the present invention. The trap circuit 10 is constituted by a series circuit consisting of a capacitor 11 and an inductance 12, and is provided between the ground and the conductor connecting the output end of the audio trap circuit 6 and the input end of the audio amplifier circuit 60. There is. The resonant frequency of the trap circuit 1o consisting of the capacitor 11 and the inductance 12 is selected to be approximately 1/2 of the interval between the audio carrier wave 180 frequency and the frequency of the upper interface channel video carrier f. Frequency of gate fatigue! Okara upper side llI contact channel carrier wave/PH
It is designed to attenuate the frequency range up to the frequency of . The composite video signals sent out as described above are combined in the picture tube through circuits that process the chrominance signal and the luminance signal, respectively, in the video amplification circuit j.

The frequency characteristics of the trap circuit 100 used in the present invention are as shown in FIG. 6, which traps the frequency range described above. For example, when receiving a television signal of the nth channel that is affected by the offset as shown in FIG. 4, the audio carrier S of the nth channel and the (n+
1) Attenuating the carrier wave in the portion where the video carrier wave P of the channel overlaps is generated, so the video signal of the (n+1) channel will not mix with the video signal of the third channel and cause screen beats. Considering the selectivity characteristics of the intermediate frequency signal amplification circuit 4 due to the provision of this audio trap circuit 1G, the attenuation level is relatively averaged over the above frequency range, and the audio carrier wave It is also possible to prevent color shift due to B) K between the color subcarrier and the color subcarrier. Also, due to fluctuations in the local oscillation frequency, the frequency of each intermediate frequency signal! Even when the /PU etc. fluctuate, the trap band of the trap circuit 10 is included in the fluctuation range of these frequencies, so the signal carrier wave frequency of the upper adjacent channel does not mix into the color signal circuit etc., and stability is maintained. performance is not impaired.

FIG. 1 is a circuit diagram showing another embodiment of the present invention. The feature of this embodiment is that a trap circuit is provided in front of the video amplifying circuit 5, which attenuates frequencies equal to or higher than the frequency of the audio carrier wave/8 and takes on the -t'-a-pass filter characteristic. In addition, this trap circuit and the circuit 1 of the previous embodiment
0 may be interposed between the conventional audio trap circuit 6 and video amplification circuit 5, or may be interposed between the intermediate frequency signal amplification circuit 4 and the audio trap circuit 6. It is installed in the front stage of 6. That is, the output terminal T of the detection circuit 3 is connected to the audio trap circuit 6 of the SMW filter via the trap circuit 13 with a low-pass filter, which is the main part of this embodiment. The configuration of the trap circuit 13 with a low-pass filter is such that a human input signal is supplied through a resistor 14 to a parallel circuit consisting of a capacitor 15 and an inductance 16, and the output end of this parallel circuit is grounded by a capacitor 17.

The frequency characteristics of the trap circuit 130 with an a-bus filter of the Eirin signal band adjustment circuit having the above configuration are as shown in FIG. Rono (trap H road 130 with filter)
The frequency at which the input signal is attenuated is in the frequency range above the audio carrier wave 80 frequency/8, 3" frequency/, #- etc. The maximum attenuation frequency (trap station wave number) is The same frequency as in the previous example is selected, and it is determined by the combined impedance of the capacitor 15, 17 and the inductance 1. When the frequency of the input signal becomes higher than this trough frequency, the capacitor and the inductance 16 are combined. 5, the amount of attenuation gradually decreases depending on the frequency.By using a trap circuit 13 having a low-pass filter characteristic, the trap-wave number reduction power is expanded due to the low-pass filter characteristic. Since it is also possible to obtain a 0-value signal in the high frequency range, it is possible to suppress the high frequency carrier wave that causes spurious interference.
There is an effect.

Although the embodiment of the present invention has been described using an example of an intermediate frequency i-signal amplification circuit with one detection circuit, it may also be applied to a circuit with two detection circuits. , one effect is to simplify the configuration -0 As stated above, according to the present invention, a desired channel is connected between the output end where the video signal is detected and the video amplification circuit that separates the color signal. Approximately 1/of the frequency interval between the frequency of the audio carrier wave and the audio carrier wave of the upper adjacent channel! By providing a trap circuit with a tuning point at the frequency of It can be improved to eliminate beat interference that interferes with the conference signal.It is also possible to suppress spurious interference due to frequencies higher than the upper adjacent channel.
It has a wide range of applications and has great effects.

[Brief explanation of drawings]

Figure 1 is a spectrum diagram showing the frequency spectrum of an NTSC television signal, Figure C is a block diagram showing the adjustment method, and Figure 71.2b is a video intermediate frequency signal amplification circuit using two conventional detection circuits. Fig. 3a is a tuning characteristic diagram showing the band adjustment characteristics of the circuit in Fig. 2a, and Fig. 3b is a tuning characteristic diagram showing the band adjustment characteristics of the circuit in Fig. 2b. , Fig. 3c is a tuning characteristic diagram showing improved characteristics from Fig. sb, Fig. 4 is a spectrum diagram when an offset is applied to the television signal in Fig. 1, and Fig. 6 is a diagram showing an example of the present invention. Schematic shown, #! 6 is a characteristic diagram showing the frequency characteristics of the trap circuit of the main part of the present invention used in FIG. 5, FIG. 7 is a circuit diagram showing another embodiment,
FIG. 8 is a characteristic diagram showing the frequency characteristics of the trap circuit to which the low-pass filter characteristic, which is the main part of the present invention, used in FIG. 7 is added. 4...Intermediate frequency layer width circuit 5...Pilot amplifier circuit 6...Audio trap circuit 10, 13...Trap circuit 11, 15, 17...Capacitor 14...Resistor 16, 62...・Inductance

Claims (1)

[Claims] (1) Between the output end of the Eirin test liquid circuit and the Eirin amplifier circuit that separates the color signal, the frequency of the image carrier wave of the upper adjacent channel and the frequency of the audio carrier wave of the receiving channel are connected. A video signal band adjustment circuit which is provided with a trap circuit that changes the tuning frequency in the frequency range 8, and whose video detection power in the frequency range is attenuated as a 4I image. (Rose) The tuning frequency of the trap circuit is selected to be approximately in the middle of the frequency range of the frequency range of the video carrier wave of the upper adjacent channel and the frequency range of the audio carrier wave of the receiving channel. Range 1st term Kffi moth video signal band adjustment circuit. (3) The shipping circuit is designed to eliminate high frequencies above the tuned frequency selected in the frequency range between the frequency of the video carrier of the upper adjacent channel and the frequency of the audio carrier of the receiving channel. Characteristic claim 1
2. The Eirin signal band adjustment circuit according to item 1 or 2.