JPH0846947A - Catv terminal equipment - Google Patents

Abstract

PURPOSE:To suppress interference for a video signal which is de-scrambled and which is demodulated to a base band signal. CONSTITUTION:A CATV terminal consists of a de-scrambling circuit 4 de- scrambling an IF video signal from a tuner, a VIF.SIF demodulation circuit 6, a key signal detection circuit 8 detecting a key signal and a video noise reduction circuit 14 removing the interference of the demodulated video base band signal. Thus, the side band component of a sound signal leaked into the video base band signal is removed by operating the video noise reduction circuit 14 with the detected key signal as a trigger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV terminal device for descrambling scrambling of a synchronous compression system.

[0002]

2. Description of the Related Art In recent years, it has become common to scramble television signals in urban CATV systems and the like to prevent eavesdropping. A synchronous compression method is widely used as this scramble method.

A conventional CATV for descrambling a video signal scrambled by a synchronous compression method will be described below.
The configuration and signal flow operation of the terminal device will be described with reference to FIGS. 4 and 5. FIG. 4 is a block diagram of a descramble peripheral circuit in a conventional CATV terminal device. 1 is a tuner for selecting and receiving a television signal including a video signal which has been subjected to synchronous compression scrambling and has been AM-modulated on an RF carrier, and a key signal which has been AM-modulated and an RF signal which has been FM-modulated on an audio signal. 4 is IF
A descrambling circuit which descrambles the IF video signal 2 converted into the signal 1 by a control signal 11 created based on the key signal 9. 6 is a video signal 5 which is converted to IF and descrambled, and an IF audio signal 3 which is converted to IF
Is a VIF / SIF demodulation circuit for demodulating the video baseband signal and the audio baseband signal. The IF voice signal 3 is converted into an intercarrier 13 by the VIF / SIF demodulation circuit 6, then FM detected and demodulated to a voice baseband signal. 8 is the intercarrier 13
It is a key signal detection circuit for performing AM detection of the key signal 9 from the audio signal converted into. A control signal 11 generates a control signal 11 based on the detected key signal 9 to control the descrambling circuit 4, and the tuner 1 is controlled by the control signal 12.
And a control circuit for controlling the entire terminal device.

Next, a method of descrambling the synchronous compression method and a signal flow operation in the terminal device will be described. The synchronous compression method is a method of scrambling by compressing each synchronization period of vertical synchronization and horizontal synchronization at a constant ratio with respect to the amplitude of the video period and transmitting the compressed data. Here, a method of descrambling the scrambling of the synchronous compression method will be described with reference to FIG.

Reference numeral 15 is an I converted from the tuner 1 to the IF.
It is a modulation waveform of an F video signal. The IF video signal 15 is obtained by compressing and synchronizing the sync period with the regular IF video signal at a constant ratio during the video period. The synchronization period compressed to the period a of the IF video signal 15 is shown. First, with respect to the IF video signal 15, the period b of the control signal 19 is based on the key signal 18 after waveform shaping.
Using the control signal 19 created at the timing of, the video period is compressed at the same ratio as the ratio at which the synchronization period is compressed. Next, the signal which is similarly compressed in the synchronization period and the video period is expanded to be descrambled. The key signal 18 is to be transmitted after being subjected to AM modulation in association with the compression timing of each horizontal synchronization on the RF carrier in which the audio signal is FM modulated.

The IF audio signal 3 selected and received by the tuner 1 and converted into an IF is input to the VIF / SIF demodulation circuit 6 with the key signal superposed thereon. The IF audio signal 3 is first converted into 4.5 MHz of the intercarrier 13 in the VIF / SIF demodulation circuit 6. Next, it is demodulated as an audio baseband signal by FM detection. Further, the key signal in which the audio signal is AM-modulated with respect to the FM-modulated RF carrier is converted into the inter-carrier and then detected by the key signal detection circuit 8 for performing AM detection, and after waveform shaping. It is input to the control circuit 10.

The control circuit 10 controls the descrambling circuit 4 by creating a control signal 11 based on the input key signal 9 at the timing of the key signal 18 and the period b in FIG.

[0008]

However, the audio signal is F
Since the key signal for descrambling is AM-modulated on the M-modulated RF carrier, sidebands of the audio signal are generated on the RF carrier. VIF / SI
The demodulation of the video baseband signal in the F demodulation circuit 6 is about 4.2 MHz band. The sideband component of the audio signal leaked by the AM modulation with the key signal leaks into the high band part of this band, and is demodulated as a video baseband signal together with the original video signal as shown by reference numeral 16 in FIG. As described in the above procedure, the key signal determines the descramble timing, and is generally inserted and transmitted near the same timing as the front porch of the video signal. Timing examples of the transmitted video signal and key signal are shown by reference numerals 16 and 18 in FIG. Here, the leakage component of the sideband component of the audio signal is applied to the leading edge of horizontal synchronization as indicated by reference numeral 17. Therefore, TV
Swinging of the horizontal synchronization of the set causes screen shaking, which interferes with the TV image.

According to the present invention, the side band component of the audio signal is prevented from leaking into the video signal, which occurs when the key signal is superimposed on the RF carrier in which the audio signal is FM-modulated, to prevent interference with the TV image. It is intended to provide a CATV terminal device for mitigation.

[0010]

CATV in the present invention
The terminal device is an RF television including a signal in which an RF carrier is FM-modulated with an audio signal, a key signal is further superimposed with an AM, and a signal in which the RF carrier is AM-modulated with a video signal and further subjected to a synchronous compression scramble. Select signal,
A tuner for receiving, and a descramble circuit for descrambling the IF video signal converted to IF by the tuner, a descrambled IF video signal, and an IF audio signal converted to IF by the tuner, respectively. VIF / SI for demodulation to baseband signals
An F demodulation circuit, a key signal detection circuit for AM-detecting a key signal from a voice signal converted into an intercarrier in the process of demodulating into a voice baseband signal in the VIF / SIF demodulation circuit, and the detected key signal In addition to a CATV terminal device having a control circuit for controlling the descrambling circuit and the terminal device as a whole, the video base demodulated by the VIF / SIF demodulating circuit using the key signal as a trigger. A video noise reduction circuit for removing a sideband component of an audio signal mixed in a band signal is provided.

[0011]

With the above construction, the CATV apparatus of the present invention operates the trap circuit included in the video noise reduction circuit with the key signal as a trigger after descrambling, thereby AM-modulating and superimposing the key signal on the video baseband. The sideband component of the audio signal leaking into the signal can be removed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A CATV terminal device according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 3 and 5. FIG.
In FIG. 4, each circuit configuration block denoted by reference numerals 1 to 11 is the same as that provided in the conventional CATV terminal device in FIG. The difference from the conventional configuration of FIG. 4 is that a video noise reduction circuit 14 is newly added in the present invention.

First, the operation of the present invention will be described with reference to FIG. 1 by dividing it into a video signal, an audio signal and a key signal. Tuner 1
The output IF video signal 2 is descrambled by the descramble circuit 4 and input to the VIF / SIF demodulation circuit 6. AM in the VIF / SIF demodulation circuit 6
By performing detection, it is demodulated into the video baseband signal 7. The demodulated video baseband signal 7 is input to the video noise reduction circuit 14.

On the other hand, the IF audio signal 3 output from the tuner 1 is V modulated with the key signal being AM-modulated and superposed.
It is input to the IF / SIF demodulation circuit 6. VIF / SIF
In the demodulation circuit 6, in order to demodulate to a voice baseband signal, first, the frequency is converted into the intercarrier 13 and the FM
It detects and demodulates to a voice baseband signal. Although the key signal is still superimposed on the intercarrier 13, the influence of the key signal does not appear in the output because the demodulation of the voice baseband signal is FM detection. The key signal superposed by AM modulation on the RF carrier is the VIF / SIF.
The signal is input to the key signal detection circuit 8 when it is converted into the intercarrier 13 by the demodulation circuit 6. In the key signal detection circuit 8, AM detection is performed, and after waveform shaping, a key signal 9 is obtained, which is a control circuit 10 and a video noise reduction circuit 14.
Is input to

The control circuit 10 generates a descramble control signal 11 based on the key signal 9 and controls the descramble circuit 4. Further, the key signal 9 is input to the video noise reduction circuit 14 as a trigger to pass the demodulated video baseband signal 7 and at the same time to operate the video noise reduction circuit 14 to remove the sideband component of the audio signal.

Next, an embodiment of the video noise reduction circuit will be described with reference to FIGS. The video noise reduction circuit shown in FIG. 2 has a transistor Tr and a resistor R.
1, a buffer circuit composed of a resistor R2, a trap circuit composed of a coil L and a capacitor C, and a switch circuit SW which is turned on and off by a key signal as a trigger. After passing through the buffer circuit, the demodulated video baseband signal enables the trap function only for a part of the period at the timing created from the key signal. FIG. 3 shows an example of characteristics of the trap circuit.

Waveforms will be described below with reference to FIGS. 2, 3 and 5. The waveform of reference numeral 15 is a modulation waveform of the IF video signal that is transmitted after the synchronization period shown in appendix a is compressed. The waveform of reference numeral 18 is a waveform obtained by detecting the key signal transmitted in synchronization with the video signal and then shaping the waveform. On the basis of the key signal waveform 18, a descramble control signal waveform 19 for compressing the video period in the synchronization period as in the case of the code a is created at the timing shown in the code b. The generated descramble control signal controls the descramble circuit to descramble the modulated waveform 15 of the IF video signal.

The descrambled and demodulated video baseband signal waveform 16 is input to the buffer circuit of FIG. 2 with the sideband component of the audio signal leaking to the position shown by reference numeral 17. The trap circuit, which turns on at the timing of the key signal waveform 18, removes the sideband component near 4.2 MHz of the audio signal and outputs the video baseband signal waveform 20.

Here, leakage of the sideband component of the audio signal will be described again. The key signal is the audio signal F
AM modulation is applied to the M-modulated RF carrier to be superimposed. At this time, sideband components due to the AM modulation are generated above and below the RF carrier.

The demodulation bandwidth of the video baseband signal in the VIF / SIF demodulation circuit 6 of FIG. 1 is about 4.2 MHz.
have. Also, the sideband component generated on the lower side of the RF carrier is A as in the video baseband signal.
Has been M-modulated. Therefore, the sideband components that enter the band of the video baseband signal are simultaneously demodulated as a video signal. As a result, the sideband component of the audio signal leaks into the video baseband signal.

[0021]

As described above, according to the present invention, the key signal is activated by operating the trap circuit included in the video noise reduction circuit by using the key signal as a trigger.
The sideband component of the audio signal that leaks into the video baseband signal when modulated and superimposed is removed to prevent interference with TV images and contribute to image quality improvement.

[Brief description of drawings]

FIG. 1 is a circuit block configuration diagram of a CATV terminal device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a trap circuit included in the video noise reduction circuit configuring FIG.

FIG. 3 is a characteristic diagram of the circuit shown in FIG.

FIG. 4 is a circuit block configuration diagram of a conventional CATV terminal device.

FIG. 5 is a diagram showing a video signal and a key signal timing of a CATV terminal device according to the related art and the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 tuner 2 IF video signal 3 IF audio signal 4 descramble circuit 5 descrambled IF video signal 6 VIF / SIF demodulation circuit 7 video baseband signal 8 key signal detection circuit 9 key signal 10 control circuit 11 descramble control signal 12 Tuning control signal 13 Audio signal converted into intercarrier 14 Video noise reduction circuit 15 Video signal with synchronous compression 16 Video baseband signal demodulated by VIF / SIF demodulation circuit 17 Depending on sideband component of audio signal Noise 18 Key signal and its timing 19 Descrambling control signal made based on 19 key signal 11 20 Video baseband signal after passing through the video noise reduction circuit

 ─────────────────────────────────────────────────── ─── Continued front page (72) Keiji Kimura, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Tetsuaki Morotomi, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A tuner for selecting and receiving a television signal, a descramble circuit for descrambling an IF video signal, a descrambled IF video signal, and IF audio converted from the tuner to IF. VIF / SIF demodulation circuit for demodulating a signal into a video baseband signal and an audio baseband signal, and a key signal detection circuit for AM-detecting a key signal from an audio signal converted into an intercarrier in the process of demodulating the audio baseband signal And a control circuit for controlling the descrambling circuit and the entire terminal device based on the detected key signal, and demodulated by the VIF / SIF demodulation circuit using the detected key signal as a trigger. Video noise reduction that removes the sideband component of the audio signal mixed in the video basic band signal CATV terminal device equipped with an operation circuit. 2. The CATV according to claim 1, wherein the video noise reduction circuit is a trap circuit that operates using a key signal as a trigger in order to remove a sideband component of the audio signal mixed in the video baseband signal.
Terminal device.