Abstract:
A method of synchronizing static or dynamic dissimilar output sampling rates of multiple outputs of an integrated switching amplifier uses the step of synchronizing dissimilar static or dynamic sampling rates of multiple outputs to yield improved sonic quality, higher efficiency, lower EMI or other benefits. According to the preferred embodiment, the synchronizing is carried out with respect to pulse leading edges.

Description:
REFERENCE TO RELATED APPLICATION 
   This application claims priority from U.S. Provisional Patent Application Ser. No. 60/697,115, filed Jul. 7, 2005, the entire content of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates generally to switching amplifiers and, in particular, to a method of synchronizing static or dynamic dissimilar output sampling rates of multiple outputs of an integrated switching amplifier. 
   BACKGROUND OF THE INVENTION 
   Switching amplifiers, known in the art for many years, provide significant efficiency benefits over pre-existing Class A/B amplifiers. As Class D amplifiers proceed down the path of increased integration, it is found that the fact of integration itself can be leveraged to provide audio performance, efficiency, and EMI benefits; yet existing integrated switching amplifiers operate no better in concert than their non-intergrated ancestors. The need exists of a method whereby integrated switching amplifiers make direct use of increased integration. 
   SUMMARY OF THE INVENTION 
   The present invention resides in the method of synchronizing static or dynamic dissimilar output sampling rates of multiple outputs of an integrated switching amplifier. The technique uses the step of synchronizing dissimilar static or dynamic sampling rates of multiple outputs to yield improved sonic quality, higher efficiency, lower EMI or other benefits. According to the preferred embodiment, the synchronizing is carried out with respect to pulse leading edges. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a timing diagram that shows synchronized output pulse widths of a four-channel integrated switching amplifier of the prior art; 
       FIG. 2  is a timing diagram that shows static treble, midrange, and bass output pulse widths of a two-channel integrated switching amplifier using the present invention; and 
       FIG. 3  is a timing diagram that shows output pulse widths of a four-channel integrated switching amplifier using dynamic output sample rates per the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows synchronized output pulse widths of a four-channel integrated switching amplifier of the prior art.  FIG. 2  shows static treble, midrange, and bass output pulse widths of a two-channel integrated switching amplifier using the present invention.  FIG. 3  shows output pulse widths of a four-channel integrated switching amplifier using dynamic output sample rates per the present invention. 
   Referring now to  FIG. 1 , the output pulse width of channel A is shown in waveform  101 , the output pulse width of channel B is shown in waveform  102 , the output pulse width of channel C is shown in waveform  103 , and the output pulse width of channel D is shown in waveform  104 . Note that the leading edges of pulses shown in traces  101 ,  102 ,  103 , and  104  are all synchronized, and all are of the same sample rate. 
   Referring now to  FIG. 2 , the treble (tweeter) output of channel A is shown in waveform  201 , the midrange output of Channel A is shown in waveform  202 , the bass (woofer) output of channel A is shown in waveform  203 , and the treble, midrange, and bass outputs of Channel B are shown in waveforms  204 ,  205 , and  206 , respectively. Integration of a signal-level crossover is assumed. Note that the pulse width leading edges in traces  204 ,  205 , and  206  are  180  degrees delayed after the pulse width leading edges in traces  201 ,  202 , and  203 . This delay distributes the instantaneous current demand on the power supply, thereby reducing power supply ripple which can be transferred to the amplifier load as distortion. Note also that the pulse width sample rate of traces  202  and  205  is half the rate of the pulse width sample rate of traces  201  and  204 ; and that the pulse width sample rate of traces  203  and  206  is one third the rate of the pulse width sample rate of traces  201  and  204 . 
   Because the highest reproducible frequency of the midrange outputs shown in traces  202  and  205  is less than that of the treble outputs shown in traces  201  and  104 , the Nyquist criterion can be satisfied by a lower sample rate. Likewise, because the highest reproducible frequency of the bass outputs shown in traces  203  and  206  is less than that of the midrange output shown in traces  202  and  205 , the Nyquist criterion can be satisfied at an even lower sample rate. Synchronization between the outputs is used to prevent heterodyne products. The benefits of the lower sampling rates used are reduced switching losses and lower EMI emissions. 
   Referring now to  FIG. 3 , four channels without crossovers are shown, similar to the outputs shown in  FIG. 1 . Note that the leading edges of the pulse widths of trace  302  and  304  are delayed by 180 degrees from the pulse widths of traces  301  and  303 , to again minimize instantaneous currents demanded of the power supply. Note that the pulse widths of trace  301  show little high-frequency content. At point  305 , the sample rate of channel A is therefore dropped to a sample rate which satisfies the Nyquist criterion of the current frequencies, but minimizes switching. Trace  302  shows channel B with constant high-frequency content, so its sample rate remains at the highest rate. Trace  303  shows channel B with only low-frequency content, so its sample rate remains reduced for the duration of the trace shown. Trace  304  starts with only low-frequency content, with resulting reduced sample rate, but, at point  306 , is presented with high-frequency content (shown by rapid dynamic pulse widths) which cause, by the current invention, an increase to the maximum sample rate to satisfy the Nyquist criterion for the current input frequencies. 
   Although two sample rates only are shown in  FIG. 3 , it is anticipated that additional output sample rates may be used with differing maximum frequencies input. Note at each sample rate change  305  and  306  that the duty cycle of the affected trace  301  or  303  remains relatively constant, to preserve the sampling integral. It is assumed that any upstream upsampling filtering as well change characteristics so as to track the specific sample rate in effect. 
   By the techniques herein, it can be seen that integration of switching amplifiers can be leveraged to yield improved sonic quality, higher efficiency, and lower EMI. Although the present invention is shown applied to pulse widths synchronized on their leading edges, use of the present technique with alternate synchronization points in the pulse widths is as well anticipated.