Recursive bitstream conversion: the reverse mode

Further results are presented of the recursive bit-stream conversion technique. In particular the sample rate conversion problem is studied to convert a low frequency bit parallel sequence with high word accuracy (such as a PCM signal) into a high frequency sequence with low word accuracy (ultimately to the 1-bit bit-stream format). It is shown that recursive bit-stream conversion is a generalization of a digital sigma-delta modulator or noise shaper. Two important advantages of recursive bit-stream conversion are emphasized. One of these is the property that upsampling and noise shaping are simultaneously performed, set that in theory separate upsampling filters are superfluous. It is shown that a modest performance penalty has to be paid for this property. The other advantage of recursive bit-stream conversion is its capability to perform the major part of the required signal processing at the lower frequency, rather than at the higher frequency as in conventional schemes. The developed theory has been verified with simulation examples