Patents by Inventor Yoshikatu Shiraishi

Yoshikatu Shiraishi has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 4328398
    Abstract: A digital multi-frequency receiver for the use in an electronic telephone exchange system for detecting MF signals (700,900, 1100, 1300, 1500 and 1700 Hz) in the CCITT No. 5 system. The digital multi-frequency receiver comprises a recursive digital filter for detecting each of the MF signals on a time divisional basis, an absolute value circuit for providing the absolute value of the output of the recursive digital filter, a comparator for comparing the output of the absolute value circuit with a variable threshold to provide the detected MF signal information, and a circuit for providing the variable threshold by selecting the maximum value from among, (i) the predetermined fixed value, (ii) the product of the value .alpha. which is less than but close to 1 and the maximum value of the variable threshold circuit in a preceding frame, and (iii) the maximum value of the output of the absolute value circuit in a present frame.
    Type: Grant
    Filed: May 9, 1980
    Date of Patent: May 4, 1982
    Assignees: Oki Electric Industry Co., Ltd., Nippon Telegraph & Telephone Public Corp.
    Inventors: Masaharu Kawaguchi, Yoshikatu Shiraishi, Kazuhiro Maruyama, Hitoshi Imagawa, Yoshimasa Kaneko