Prevention of audio pop in a digital audio device

Abstract

An electronic audio device with a digital audio output channel in which an amplifier output voltage is gradually ramped up and down to avoid causing a popping sound when the device is turned on and off. This is accomplished without employing any additional hardware, by incrementally changing a digital input word applied to a digital audio source, such as a DSP, so as to gradually change the amplifier output voltage between a minimum, such as zero volts, and a DC working voltage. On powering up, the amplifier is only turned on after the digital word is applied, but while it still results in a minimum amplifier output, and on powering down the amplifier is turned off after it's output has been ramped down, but before removing the digital input word. Sources and output channels can also be switched over by powering down, and then powering up, following the same method.

What is claimed is:  
     
         1 . A method of applying power to a digital audio channel, comprising: 
 applying a digital input signal to said digital audio channel, said digital input signal initially having a value such that a DC output voltage of said digital audio channel is at a minimum;    gradually increasing said value of said digital input signal independent of an input audio signal such that said DC output voltage increases gradually until said DC output voltage is equal to a working voltage; and then    passing said input audio signal through said digital audio channel.    
     
     
         2 . The method of applying power to a digital audio channel according to  claim 1 , further comprising: 
 turning on an audio amplifier stage in said digital audio channel after said step of applying said digital input signal and before said step of gradually increasing said value of said digital input signal.    
     
     
         3 . The method of applying power to a digital audio channel according to  claim 2 , wherein said step of turning on said audio amplifier stage comprises: 
 applying power to said audio amplifier stage.    
     
     
         4 . The method of applying power to a digital audio channel according to  claim 2 , wherein said step of turning on said audio amplifier stage comprises: 
 connecting said audio amplifier stage to an audio transducer.    
     
     
         5 . The method of applying power to a digital audio channel according to  claim 1 , wherein: 
 said minimum is a potential of a ground reference of said audio amplifier stage.    
     
     
         6 . A method of removing power from a digital audio channel, comprising: 
 halting an input audio signal from passing through said digital audio channel; and    gradually decreasing a value of a digital input signal from a point of said halted input audio signal such that a DC output voltage of an amplifier of said digital audio channel decreases gradually until said DC output voltage is at a minimum.    
     
     
         7 . The method of removing power from a digital audio channel according to  claim 6 , further comprising: 
 turning off said amplifier after said step of gradually decreasing said value of said digital input signal.    
     
     
         8 . The method of removing power from a digital audio channel according to  claim 7 , wherein said step of turning off said amplifier comprises: 
 removing power from said amplifier.    
     
     
         9 . The method of removing power from a digital audio channel according to  claim 7 , wherein said step of turning off said amplifier comprises: 
 disconnecting said amplifier from an audio transducer.    
     
     
         10 . The method of removing power from a digital audio channel according to  claim 6 , wherein: 
 said minimum is a potential of a ground reference of said amplifier.    
     
     
         11 . A digital audio channel of a wireless telephone, comprising: 
 means for applying a digital input signal to said digital audio channel, said digital input signal initially having a value such that a DC output voltage of said digital audio channel is at a minimum;    means for gradually increasing said value of said digital input signal independent of an input audio signal such that said DC output voltage increases gradually until said DC output voltage is equal to a working voltage; and then    means for passing said input audio signal through said digital audio channel.    
     
     
         12 . The digital audio channel of a wireless telephone according to  claim 11 , further comprising: 
 means for turning on an audio amplifier stage in said digital audio channel after said step of applying said digital input signal and before said step of gradually increasing said value of said digital input signal.    
     
     
         13 . The digital audio channel of a wireless telephone according to  claim 12 , wherein said means for turning on said audio amplifier stage comprises: 
 means for applying power to said audio amplifier stage.    
     
     
         14 . The digital audio channel of a wireless telephone according to  claim 12 , wherein said means for turning on said audio amplifier stage comprises: 
 means for connecting said audio amplifier stage to an audio transducer.    
     
     
         15 . The digital audio channel of a wireless telephone according to  claim 11 , wherein: 
 said minimum is a potential of a ground reference of said audio amplifier stage.    
     
     
         16 . Apparatus for removing power from a digital audio channel, comprising: 
 means for halting an input audio signal from passing through said digital audio channel; and    means for gradually decreasing a value of a digital input signal from a point of said halted input audio signal such that a DC output voltage of an amplifier of said digital audio channel decreases gradually until said DC output voltage is at a minimum.    
     
     
         17 . The apparatus for removing power from a digital audio channel according to  claim 16 , further comprising: 
 means for turning off said amplifier after said means for gradually decreasing said value of said digital input signal decreases said value to said minimum.    
     
     
         18 . The apparatus for removing power from a digital audio channel according to  claim 17 , wherein said means for turning off said amplifier comprises: 
 means for removing power from said amplifier.    
     
     
         19 . The apparatus for removing power from a digital audio channel according to  claim 17 , wherein said means for turning off said amplifier comprises: 
 means for disconnecting said amplifier from an audio transducer.    
     
     
         20 . The apparatus for removing power from a digital audio channel according to  claim 16 , wherein: 
 said minimum is a potential of a ground reference of said amplifier.