JPH06233157A - Received tv signal processing circuit for catv - Google Patents

Abstract

PURPOSE:To obtain the same effect as a synchronous lock system dispensing with the system and further to obtain simplified and low-priced circuit configuration as well. CONSTITUTION:A received TV signal, on which a GCR signal is superimposed, is converted to a prescribed IF signal by a down converter 1, the pertinent IF signal is detected by a detection circuit 4 and a video signal is obtained. Concerning the video signal, the ghost component is removed by the GCR signal at a ghost removing circuit 9, the signal is modulated again by a modulator 5, and the modulated output is converted to the TV signal at the same frequency as that of the received TV signal by an up converter 6. The IF signal is branched by a branching circuit 13 and impressed to a high frequency divider 11. The signal component at the same frequency as that of the IF signal is obtained from the rectangular wave signal of the frequency divided output by a BPF 12, and the component is supplied to the modulator 5 as a carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving TV signal processing circuit for CATV, and more particularly to improvement of carrier generating means of a TV co-channel retransmitting circuit in a CATV device.

[0002]

2. Description of the Related Art When terrestrial radio waves are used for television broadcasting, radio waves are reflected by skyscrapers and the like, resulting in double reception screens, so-called ghost interference. As a countermeasure, the reference signal (Ghost
Cancel Reference, GCR signal) is superimposed on the video signal,
An apparatus that detects this GCR signal on the receiving side and removes the ghost component by this is disclosed in, for example, Japanese Patent Laid-Open No. 1077/1992
Proposed in No. 6 etc.

Thus, such a GCR in a CATV device
When receiving a video signal including a signal, a reception video signal processing circuit having the configuration shown in FIG. 2 or 3 is used for each channel for removing a ghost.

In FIG. 2, 1 is a down converter, 2
Is a local oscillator, 3 is an IF amplifier, 4 is a detection circuit, 5 is a modulator, 6 is an up converter, 7 is a PLL circuit, and 8 is V.
CO (voltage controlled oscillator), 9 is a ghost elimination circuit. The received TV signal applied to the input terminal IN is downconverted in frequency by the downconverter 1 to be converted into an IF signal of a predetermined frequency, and this IF signal is converted into an IF amplifier 3
The video signal obtained by being detected by the detection circuit 4 after being amplified by is given to the ghost removal circuit 9, and the ghost component is removed by the GCR signal.

The video signal from which the ghost component has been removed is re-modulated by the modulator 5, and the modulated output is converted into a TV signal having the same frequency as the received TV signal by increasing the frequency thereof by the up converter 6 and the output terminal OUT. Is output to. In the circuit of FIG. 3, reference numeral 10 is a perfect synchronous detection circuit incorporating a VCO 8, and the operation of the circuit of FIG. 3 is almost the same as that of the circuit of FIG.

[0006]

In the circuit of FIG. 2 or 3, the output frequency signal of the local oscillator 2 is supplied to the down converter 1 and the up converter 6 to perform the above frequency conversion. In that case, It is assumed that the frequency f _{1 of the} IF signal and the frequency f _{2 of the} modulation output are the same.

However, this assumption is not normally satisfied as it is, and the same channel beat is always generated. Therefore, in the circuit of FIG. 2, the VCO 8 for supplying the carrier to the modulator 5 is phase-locked by the PLL circuit 7 and f ₁ The frequencies f ₂ are set to be exactly the same. In the circuit of FIG. 3, the same effect is obtained by using the perfect synchronous detection circuit 10.

As described above, in the conventional circuits shown in FIGS. 2 and 3, it is necessary to adopt the above-mentioned system called the synchronization lock in order to prevent the occurrence of the same channel beat. for that reason,
Since a PLL circuit, VCO, etc. must be used, there is a problem that the circuit configuration is complicated and the cost is high. Further, when the VCO is used, there is a problem that the self-excitation of the residual FM causes deterioration of C / N and the like, which adversely affects the image quality.

Therefore, an object of the present invention is to provide a receiving TV signal processing circuit for CATV which can obtain the same effect as the above without using the synchronous lock system and can have a simple and inexpensive circuit structure.

[0010]

In order to achieve the above object, the present invention converts a received TV signal on which a GCR signal is superimposed into a predetermined IF signal by a down converter,
A video signal obtained by detecting the IF signal is processed by the GCR signal to remove a ghost component and modulated again by a modulator, and the modulation output is upconverted by an up converter to a TV having the same frequency as the received TV signal. In a CATV reception TV signal processing circuit for converting and outputting a signal, a frequency dividing means for dividing the IF signal and a filter for extracting a signal component of the same frequency as the IF signal from a frequency division output of the frequency dividing means. And a means for supplying the signal component of the filter means to the modulator as a carrier signal.

[0011]

From the frequency-divided output of the IF signal, a signal component having the same frequency as the IF signal is given to the modulator as a carrier. Therefore, the frequency of the IF signal and the frequency of the modulated output are kept exactly the same, the occurrence of the same channel beat is prevented, and the circuit configuration is simplified.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a receiving TV signal processing circuit for one channel provided in a CATV device as an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 2 represent the same or similar circuits, and the configuration different from the circuit in FIG.
Instead of the L circuit and the VCO, the high frequency divider 11 and the IF
A BPF (bandpass filter) 12 for use is used. Reference numeral 13 is a branch circuit. The IF signal branched by the branch circuit 14 is added to the high frequency divider 11. If the high frequency divider 11 is a signal having an appropriate input level,
Even if the signal is a modulated wave, it is divided and a square wave signal is obtained as the divided output. Since this square wave signal contains infinite high frequency components, naturally, it also contains signal components having the same frequency as the original IF signal. Therefore, the BPF 12 extracts the signal component from the square wave signal and supplies it to the modulator 5 as a carrier.

In the present embodiment, the operation of detecting the video signal from the IF signal, removing the ghost component, modulating it, and converting it again into a TV signal is the same as in the conventional circuit described above.

In the circuit configuration of this embodiment, a signal component having the same frequency as the IF signal is extracted from the square wave signal obtained by dividing the IF signal and used as the carrier of the modulator. It is possible to prevent the occurrence of co-channel beats without using a simple synchronization lock method.

[0015]

As described above, according to the present invention, since the conventional synchronous lock system is not adopted, a circuit such as a VCO is not necessary, and the circuit configuration is simple and inexpensive. Also VC
Since O is not used, the residual FM component is only the residual FM component by the IF conversion local oscillator, and the adverse effect on the image is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional received TV signal processing circuit for CATV.

FIG. 3 is a block diagram showing another example of a conventional receiving TV signal processing circuit for CATV.

[Explanation of symbols]

 1 Down Converter 2 Local Oscillator 4 Detection Circuit 5 Modulator 6 Up Converter 9 Ghost Removal Circuit 11 High Frequency Divider 12 BPF

Claims (1)

[Claims] 1. A received TV signal on which a GCR signal is superimposed is converted into a predetermined IF signal by a down converter,
A video signal obtained by detecting the IF signal is processed by the GCR signal to remove a ghost component and modulated again by a modulator, and the modulation output is upconverted by an up converter to a TV having the same frequency as the received TV signal. In a CATV reception TV signal processing circuit for converting and outputting a signal, a frequency dividing means for dividing the IF signal and a filter for extracting a signal component of the same frequency as the IF signal from a frequency division output of the frequency dividing means. Means for supplying the above-mentioned signal component of the filter means to the modulator as a carrier signal, and a receiving TV signal processing circuit for CATV.