Ingress noise control system and ingress noise blocking device

• US 6,868,552 B1
• Filed: 06/07/2000
• Issued: 03/15/2005
• Est. Priority Date: 06/07/1999
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited, Miharu Communications Company Limited
• Original Assignee: Fujitsu Limited, Miharu Communications Company Limited
• Inventors: Inoue, Kazunari, Tamura, Hiroo, Tyou, Takayuki, Ishida, Minoru, Masuda, Shigefumi
• Primary Examiner(s): Miller, John
• Assistant Examiner(s): BELIVEAU, SCOTT E
• Application Number:
  US09/589,426
• Time in Patent Office: 1,742 Days
• Field of Search: 725/124, 725/125, 725/127, 725/128, 327/552
• US Class Current: 725/125
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

The present invention concerns an ingress noise control system and an ingress noise blocking device which are used in a cable system to suppress ingress noise. In the cable system providing two-way communication using different frequency bands for transmission of upstream and downstream signals, the ingress noise control system includes, within a distribution unit, a two-way amplification unit, etc. provided in an upstream signal transmission path, a synchronous detection controller 6 for synchronously detecting the upstream signal transmitted from terminal equipment and separated by a low-pass filter 4 in a second separation filter 2, a gate switch circuit 5 which is turned on by the synchronous detection controller 6 to pass the upstream signal only when the upstream signal is synchronously detected, and an indicator 7 for indicating the on/off state of the gate switch circuit 5.

Claims

1. An ingress noise blocking device comprising:

first and second separation filters for separating upstream and downstream signals using different frequency bands in a cable system;

a gate switch circuit for passing or not passing the upstream signal between the first and second separation filters; and

a synchronous detection controller for turning on the gate switch circuit only when the upstream signal is synchronously detected;

wherein the synchronous detection controller has a differential detection circuit configuration which includes a delay circuit for delaying the upstream signal and a synchronous detector for multiplying the upstream signal by the signal delayed by the delay circuit.

2. An ingress noise control system for use in a cable system providing two-way communication using different frequency bands for transmission of upstream and downstream signals, comprising:

an ingress noise blocking device, which includes a synchronous detection controller and a gate switch circuit, and which turns on the gate switch circuit only when an upstream signal is synchronously detected, to pass the upstream signal therethrough, the ingress noise blocking device provided in a transmission path of the upstream signal; and

which further includes a spectrum detector for judging whether or not the upstream signal is a valid upstream signal, based on a comparison of the upstream signal level for each of a plurality of distinct predetermined frequencies when the upstream signal is synchronously detected by the synchronous detection controller, and for turning on the gate switch circuit to pass the valid upstream signal therethrough only when the upstream signal is judged to be a valid upstream signal;

wherein the synchronous detection controller has a differential detection circuit configuration which includes a delay circuit for delaying the upstream signal and a synchronous detector for multiplying the upstream signal by the signal delayed by the delay circuit.

3. An ingress noise blocking device comprising:

first and second separation filters for separating upstream and downstream signals using different frequency bands in a cable system;

a gate switch circuit for passing or not passing the upstream signal between the first and second separation filters;

a synchronous detection controller for turning on the gate switch circuit only when the upstream signal is synchronously detected; and

a spectrum detector which obtains a spectrum of the upstream signal synchronously detected by the synchronous detection controller and which, based on a comparison of signal levels for each of a plurality of distinct predetermined frequencies, further judges whether or not the upstream signal is a valid upstream signal, and turns on the gate switch circuit only when the upstream signal is judged to be a valid upstream signal;

wherein the synchronous detection controller has a differential detection circuit configuration which includes a delay circuit for delaying the upstream signal and a synchronous detector for multiplying the upstream signal by the signal delayed by the delay circuit.

4. An ingress noise blocking device comprising:

first and second separation filters for separating upstream and downstream signals using different frequency bands in a cable system;

a gate switch circuit for passing or not passing the upstream signal between the first and second separation filters;

a synchronous detection controller for turning on the gate switch circuit only when the upstream signal is synchronously detected; and

a synchronous detection judging unit which obtains a spectrum of the upstream signal synchronously detected by the synchronous detection controller and which, based on the ratio of signal levels at predetermined frequencies, judges whether or not the upstream signal is a valid upstream signal, and turns on the gate switch circuit only when the upstream signal is judged to be a valid upstream signal;

wherein the synchronous detection controller has a differential detection circuit configuration which includes a delay circuit for delaying the upstream signal and a synchronous detector for multiplying the upstream signal by the signal delayed by the delay circuit.

5. An ingress noise blocking device comprising:

first and second separation filters for separating upstream and downstream signals using different frequency bands in a cable system;

a gate switch circuit for passing or not passing the upstream signal between the first and second separation filters; and

a synchronous detection controller for turning on the gate switch circuit only when the upstream signal is synchronously detected;

wherein the synchronous detection controller comprises;

a band-pass filter for passing only the upstream signal falling within a prescribed frequency band;

a delay circuit for delaying the signal passed through the band-pass filter, a synchronous detection circuit for performing synchronous detection using the signal passed through the band-pass filter and the signal delayed through the delay circuit;

a low-pass filter for generating a baseband signal from a detected signal supplied from the synchronous detection circuit; and

a synchronous detection judging unit for judging the presence or absence of the upstream signal based on the presence or absence of the baseband signal from the low-pass filter.

6. An ingress noise blocking device according to claim 5, wherein the synchronous detection controller further includes a spectrum detector for detecting a spectrum of the upstream signal, and wherein the synchronous detection judging unit judges the presence or absence of the upstream signal based on the presence or absence of the baseband signal from the synchronous detection circuit and on spectral characteristics directed by the spectrum detector.