Multi-frequency signal receiver and a method of detecting the multi-frequency signal

Patent 5214693 Issued on May 25, 1993. Estimated Expiration Date:

October 2, 2010. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.

Abstract Claims Description Full Text

Patent References

3710031

3795775

3812432

3845249

Apparatus for distinguishing voice and other noise signals from legitimate multi-frequency tone signals present on telephone or similar communication lines
Patent #: 3944753
Issued on: 03/16/1976
Inventor: Proctor , et al.

Dual tone multifrequency signal receiver
Patent #: 4206323
Issued on: 06/03/1980
Inventor: Padgett , et al.

Multifrequency tone detector
Patent #: 4386239
Issued on: 05/31/1983
Inventor: Chien

Dual tone multi frequency digital detector
Patent #: 4484035
Issued on: 11/20/1984
Inventor: Graham , et al.

Apparatus for multifrequency signalling tone detection
Patent #: 4599495
Issued on: 07/08/1986
Inventor: Richards

Digital multifrequency signal receiver Patent #: 4626629
Issued on: 12/02/1986
Inventor: Premoli , et al.

Inventor

Chujo, Kaoru

Application

No. 591939 filed on 10/02/1990

US Classes:

379/386, Signal receiver (e.g., tone decoder)327/47, Frequency detection379/283, Dual tone multifrequency (DTMF) receiver379/351Signalling integrity protection (e.g., voice signal immunity)

Examiners

Primary: Dwyer, James L.
Assistant: Shehata, M.

Attorney, Agent or Firm

Staas & Halsey

Foreign Patent References

8401044 IB 03/13/1984
0144493 JP 06/13/1987
1-138889 JP. 05/13/1989
1-188194 JP. 07/13/1989
1-243690 JP. 09/13/1989
0305694 JP 12/13/1989

International Class

H04M 001/50

Foreign Application Priority Data

1989-10-18 JP

Abstract

A multi-frequency signal receiver, and in particular a push-button signal receiver, is provided having a detector circuit and an amplitude variation supervisory circuit. The detector circuit has a group of band pass filters, each having a pass band corresponding to each elemental signal in the multi-frequency signal. The detector circuit also has a logic circuit for receiving each output from the band pass filters and outputting detected data of the multi-frequency signal. The amplitude variation supervisory circuit monitors the amplitude of an input signal for a predetermined duration and detects and holds the maximum value of the monitored amplitude. Then, the amplitude variation supervisory circuit detects when the amplitude of the input signal exceeds the maximum amplitude value to determine if the input signal is not the multi-frequency signal.