A direct digital synthesizer with interpolation circuits

This paper presents a direct digital synthesizer (DDS) with no ROM that still produces square waves with low spurious signals. The main features are the interpolation of the analog-converted accumulator contents and the extraction of timing at the points where the interpolated signal is identical to a continuous sawtooth waveform. Experimental results confirm successful frequency synthesizer operation. The output frequency is determined by the frequency control word, and spurious signals present in the accumulator contents are greatly reduced.