Browse Prior Art Database

Low Noise Filtering for Audio Talker Circuits

IP.com Disclosure Number: IPCOM000040213D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Morizio, J: AUTHOR

Abstract

A technique is described whereby audio noise, propagating from audio amplifier circuits, is filtered out by means of voltage regulators, resistive/capacitance (RC) filtering and ground isolation methods as applied to analog and digital coupling circuitry. Digital circuitry placed in close proximity to analog amplifier circuits, which may contain unique device operational functions, such as continuous variable slope delta (CVSD) modulation, linear predictive coding (LPC) or analog filtering, have been found to emit unwanted audio noise from the amplified speakers. The technique described herein filters out the unwanted noise so that signals from digital circuitry converted to analog sound-producing signals will be much more intelligible.

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Low Noise Filtering for Audio Talker Circuits

A technique is described whereby audio noise, propagating from audio amplifier circuits, is filtered out by means of voltage regulators, resistive/capacitance (RC) filtering and ground isolation methods as applied to analog and digital coupling circuitry. Digital circuitry placed in close proximity to analog amplifier circuits, which may contain unique device operational functions, such as continuous variable slope delta (CVSD) modulation, linear predictive coding (LPC) or analog filtering, have been found to emit unwanted audio noise from the amplified speakers. The technique described herein filters out the unwanted noise so that signals from digital circuitry converted to analog sound-producing signals will be much more intelligible. To provide the proper filtration to reduce or eliminate unwanted noise, first the +5v and -5v power supplies are independently regulated. Then RC filters are installed, as shown in the figure. The values of the RC filters are matched to the reflective impedances of the +5v and -5v analog loads. Next, the circuit card containing both digital and analog portions of the circuit are physically separated by as much as a quarter inch, so as to reduce the effects of noise-coupled grounding.

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