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:
Sep. 09, 1997
Filed:
May. 10, 1994
Gregory S Gillespie, Nevada City, CA (US);
Thomas J Glad, Nevada City, CA (US);
TDK U.S.A. Corporation, Port Washington, NY (US);
Abstract
Method and apparatus for controlling the volume of an internal PC speaker. In the present invention, pulse width modulation (PWM) techniques are used to selectively reduce the signal power generated at the speaker. By substituting a high frequency signal having a symmetric duty cycle for portions of the digital audio signal, the average signal power is reduced. The frequency of the substitute signal is much higher than the speaker bandwidth, contributing negligible power to the output. The ratio of audio signal to high frequency signal determines the output signal level. In the preferred embodiment of the present invention, a three bit counter is used to separate the audio signal into intervals having eight states apiece. A signal providing -6 dB of attenuation is generated by substituting the toggling output from the least significant bit of the counter during four out of the eight states. A signal providing -12 dB of attenuation is generated by substituting the same toggling output during six out of the eight states. A multiplexer is provided to select between the two attenuated signals, an unattenuated signal and a DC signal (off).