Amplifiers – Combined with automatic amplifier disabling switch means
Patent
1994-02-02
1995-06-13
Mottola, Steven J.
Amplifiers
Combined with automatic amplifier disabling switch means
381120, H03F 114
Patent
active
054246784
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.
REFERENCES:
patent: 5142238 (1992-08-01), White
patent: 5229719 (1993-07-01), Tagiri
Austin Steven E.
Gurries Mark C.
Heyl Lawrence F.
Apple Computer Inc.
Mottola Steven J.
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