A sigma delta class D device that uses a low pass filter to smooth the output
waveform
and eliminate high frequency switching noise from the feedback value includes:
a first summing node having a positive input coupled to a signal input node; a
second summing node having a first positive input coupled to an output of the first
summing node and having an output coupled to a signal output node; a low pass filter
having an input coupled to the output of the second summing node; an analog to
digital converter having an input coupled to an output of the low pass filter;
a third summing node having a positive input node coupled to an output of the analog
to digital converter and a negative input node coupled to the output of the first
summing node; and a feedback device coupled between an output of the third summing
node and a negative input of the first summing node.