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METHOD AND CIRCUIT FOR PROGRESSIVE GAIN SETTING OF AUDIO AMPLIFIERS AT START-UP

IP.com Disclosure Number: IPCOM000007951D
Publication Date: 2002-May-07
Document File: 3 page(s) / 32K

Publishing Venue

The IP.com Prior Art Database

Abstract

During start-up of an audio amplifier, some parts of the circuitry around the amplifier take various times to settle which generates an idle fast transient signal resulting in a sound like an aggressive "pop" to the user. One prior art solution to reduce or eliminate the undesirable popping sound includes placing the amplifier in active mode after the common mode voltage has reached a given value to allow circuitry to settle. This approach has resulted in undesirably slow, amplifier start-up times. Other solutions include gain alteration, such as holding the amplifier gain at a low level initially, allowing the output to settle gently to the common mode. A problem with prior art gain alteration techniques has been the means or methods used to return the gain to operation levels is too abrupt, resulting in aggressive noise at the output. Therefore, it would be advantageous to provide a method and circuit for progressive gain setting of audio amplifiers at start-up that overcomes the problems of prior art including aggressive audible popping sounds and slow start-up times.

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METHOD AND CIRCUIT FOR Progressive gain setting of audio amplifiers at start-up

During start-up of an audio amplifier, some parts of the circuitry around the amplifier take various times to settle which generates an idle fast transient signal resulting in a sound like an aggressive “pop” to the user.  One prior art solution to reduce or eliminate the undesirable popping sound includes placing the amplifier in active mode after the common mode voltage has reached a given value to allow circuitry to settle.  This approach has resulted in undesirably slow, amplifier start-up times.

Other solutions include gain alteration, such as holding the amplifier gain at a low level initially, allowing the output to settle gently to the common mode.  A problem with prior art gain alteration techniques has been the means or methods used to return the gain to operation levels is too abrupt, resulting in aggressive noise at the output. 

Therefore, it would be advantageous to provide a method and circuit for progressive gain setting of audio amplifiers at start-up that overcomes the problems of prior art including aggressive audible popping sounds and slow start-up times.

                     In audio amplifiers the common mode voltage (DC value of the output signal) is called VMC. The common mode voltage  is often set to Vsupply/2 by the means of a resistive divider.  An external high value decoupling capacitor allows improvement of the supply rejection ratio of the amplifier (as VMC doesn’t follow the high frequency variations of the supply voltage) and allows VMC...