Double Interpolation for Digital-to-Analog Conversion

Interpolative digital-to-analog converters generate an output that has only a few analog levels. They provide fine resolution by oscillating rapidly between these levels in such a manner that the average output represents the value of the applied code. Here we describe an improved method of interpolating that results in reduced noise in the signal band. A theory of the interpolation, confirmed by experiments, demonstrates that switching between only two levels at 1.3 mHz could provide 16 bit resolution for telephone signals.