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 2 levels at 1.3 MHz can provide 16-bit resolution for telephone signals.