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. 13, 1995
Filed:
Feb. 02, 1994
Lawrence F Heyl, Mountain View, CA (US);
Mark C Gurries, San Jose, CA (US);
Steven E Austin, San Jose, CA (US);
Apple Computer, Inc., Cupertino, CA (US);
Abstract
A technique is provided for substantially reducing clicks and pops caused by power cycling, in particular, the power cycling conservation strategy used in a portable computer. More specifically, an audio amplifier arrangement for a computer, in accordance with one embodiment of the present invention, includes a differential amplifier having a first input terminal, a second input terminal and an output terminal. A sound output connector may be connected to the output terminal through a signal path. First switching circuitry is responsive to a first mute signal for connecting together the first input terminal and the second input terminal through a low-impedance path. As a result, an output signal produced by the differential amplifier is essentially forced to zero. When power is removed from or applied to the differential amplifier, however, its behavior is not entirely predictable, and the output signal produced cannot be guaranteed to remain zero throughout the power-down transition. Therefore, further in accordance with the invention, second switching circuitry is responsive to a second mute signal for substantially interrupting the signal path by switching a high impedance into the signal path. In a preferred embodiment, the first switching circuitry and the second circuitry are realized by MOSFETs which in cascade yield approximately 120 dB of attenuation, inaudible to a user by any standard.