CATV converter for receiving both analog and digital signals

Details CATV converter for receiving both analog and digital signals CATV converter for receiving both analog and digital signals

1997-03-27

1999-04-06

Faile, Andrew I.

Telecommunications

Interference signal transmission

333174, 333176, 348 10, 348554, 348726, 455339, 455266, H04H 102, H04N 710, H03H 700

Patent

active

058930256

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a CATV converter for digital and analog signals.


BACKGROUND OF THE INVENTION

A conventional CATV converter, as illustrated in FIG. 7, comprises: fed to a first terminal of the first mixer 52, and an output from the first local oscillator 51 is also fed to a second terminal thereof, mixer 52 is fed, 53 is fed to a first terminal of the second mixer 55, and an output of the second local oscillator 54 is also fed to a second terminal thereof, mixer 55, and circuit 56. this order: a first filter 58, a first amplifier 59, a second filter 60, and a second amplifier 61.
An operation of the above conventional CATV is explained here:
A signal fed into the input terminal 57A is mixed in the first mixer 52 whereby being converted to a first intermediate frequency. The output thereof is fed to the intermediate filter 53, and only an intermediate frequency bandwidth is tapped off. The output thereof is fed to the second mixer 55, whereby being converted to the second intermediate frequency before being tapped off. The output thereof is fed to the output circuit 56, and then tapped off from the output terminal 57B. In the output circuit 56, a signal tapped off from the second mixer 55 is fed to the first filter 58, where a video carrier of an upper adjacent channel and an audio carrier of a lower channel are attenuated and then tapped off. The output thereof is fed to the first amplifier 59 and amplified, then tapped to the second filter 60, where an audio carrier of the upper adjacent channel and a video carrier of the lower channel are attenuated and then tapped off. Further the output thereof is fed to the second amplifier 61 to be amplified, then tapped off.
In this conventional structure, a trap is provided nearby the received signal bandwidth because of the first filter 58. Therefore, in the system which handles digital and analog signals, when receiving compressed digital signals, original signals cannot be reproduced due to deterioration of a differential phase or differential gain in the receiving signal bandwidth.


DISCLOSURE OF THE PRESENT INVENTION

The present invention aims to provide a CATV converter which can receive both of digital and analog signals, and solve the above problem.
An output circuit of the CATV converter according to the present invention comprises: a first filter attenuates frequencies approximately equal to an audio carrier of an upper adjacent channel and video carrier of a lower adjacent channel, where a second filter attenuates a video carrier of the upper adjacent channel and an audio carrier of the lower adjacent carrier, terminal, and has the following function: when an input signal fed to the input terminal is within a predetermined frequency range, the input and output terminals of the second filter are short-circuited because of a high frequency of the input signal.
According to the above structure, when receiving analog signals, the second filter works to realizes an attenuation characteristic, and when receiving digital signals, the second filter is short-circuited due to a high frequency of the signals so that a passing characteristic in the bandwidth may be flat, whereby providing a CATV converter which can receive digital/analog signals without deterioration.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram according to an exemplary embodiment of the present invention.
FIG. 2 is a circuit diagram of an output circuit according to a first exemplary embodiment of the present invention.
FIG. 3 is a circuit diagram of an output circuit according to a second exemplary embodiment of the present invention.
FIG. 4 is a frequency distribution chart of an input signal.
FIG. 5 depicts signals of each part.
FIG. 6 is a frequency distribution chart of a digital signal.
FIG. 7 is a block diagram of a conventional CATV converter.


DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT

FIG. 1 is a block diagram of a CATV converter according to an exemplary embodiment. As depicted in FIG. 1, the CATV converter

REFERENCES:
patent: 4827509 (1989-05-01), Izumiyama
patent: 5159711 (1992-10-01), Ma et al.
patent: 5638112 (1997-06-01), Bestler et al.
patent: 5748262 (1998-05-01), Boie
International Search Report (w/translation).

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