The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 08, 1982
Filed:
Apr. 17, 1980
Yoshikazu Ikeda, Tama, JP;
Kokusai Denshin Denwa Co., Ltd., Tokyo, JP;
Abstract
An apparatus for detecting a tone signal in a telephone switching system is provided in which a calculation, in particular, multiplication is performed by a table look-up process in a digital memory, instead of using a conventional complicated multiplier. A tone signal of a particular frequency in a telephone line is detected through a discrete Fourier transform process (DFT), by the calculation of s(i)=x(iT).times.sin(i2.pi.fT), c(i)=x(iT).times.cos(i2.pi.fT), S=.SIGMA.s(i), C=.SIGMA.c(i), and P=S.sup.2 +C.sup.2. In the above calculation, the multiplication (x(iT).times.sin(i2.pi.fT), and x(iT).times.cos(i2.pi.fT)) is performed by a table look up method in a read only memory (ROM). Thus, the calculation is simplified. Further, the ROM has cells for only the discrete particular levels of multiplicands and/or the multipliers to reduce the capacity of the ROM, and the ROM is referred to by the multiplicand and/or the multiplier through the conversion of the same by a coefficient number generator.