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In summary, the map interprets a P-bit numeric value at its input as an angle and converts it to a D-bit sinusoidal amplitude value at its output. In a typical DDS, the input bus of the map is the N-bit output bus of the accumulator truncated to P bits. That is, in a typical DDS, N is greater than P so the map uses the most significant P-bits of the accumulator output. The D-bit output of the map connects to the D-bit input of a DAC, where the digital sinusoidal samples are converted to an analog proxy in the form of a voltage or current. In order for the map output to guarantee half LSB amplitude precision, the map's angular resolution must be at least 3 bits greater than its amplitude resolution. That is, P must be D plus 3 or greater. It is important to realize the phase truncation resulting from allowing P to be less than N does not impact the frequency resolution of the DDS. It is the accumulator rollover rate that sets the DDS output frequency, which depends only on the capacity of the accumulator C (which is related to N), the value of the FTW and the frequency of the system clock, Fs.
