Title:
IN-BAND SIGNAL EQUIPMENT
Document Type and Number:
Japanese Patent JP3036944
Kind Code:
B2
Abstract:
PURPOSE: To reduce nuisance noise by removing a component within the range of a frequency which is higher than the frequency of ring-back tone among quantization noise components which deteriorate call quality at the time of a calling operation.
CONSTITUTION: A transmitting circuit 10 transmits at least one single frequency signal corresponding to presence or absence of a signaling signal. In a receiving circuit 20, an analog signal supplied to a terminal 7 is converted into a digital signal in an A/D converter 21. An output signal from the A/D converter 21 is supplied to a detecting circuit 22 and presence or absence of the single frequency signal is detected. The output signal from the A/D converter 21 is supplied to a digital filter 23, its single frequency signal is removed and, moreover, it is supplied to a low-pass filter 24 where the frequency of ring-back tone is removed. The outputs of the filter 23 and the output of the A/D converter 21 are changed-over in accordance with the output of the detecting circuit 22.
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Inventors:
Hitoshi Fuda
Shinji Torii
Shinji Torii
Application Number:
JP1037292A
Publication Date:
April 24, 2000
Filing Date:
January 23, 1992
Export Citation:
Assignee:
NEC
NEC Engineering Co., Ltd.
NEC Engineering Co., Ltd.
International Classes:
H04M7/00; (IPC1-7): H04M7/00
Domestic Patent References:
| JP5521616A |
Attorney, Agent or Firm:
Yosuke Goto (1 person outside)