Editing Direct digital synthesis (section)

==Overview==
[[File:Direct digital synthesizer block diagram.png|frame|Figure 1 - Direct Digital Synthesizer block diagram]]

A basic Direct Digital Synthesizer consists of a frequency reference (often a [[crystal oscillator|crystal]] or [[surface acoustic wave|SAW]] oscillator), a [[numerically controlled oscillator]] (NCO) and a [[digital-to-analog converter]] (DAC) {{#tag:ref|While some authors use the terms DDS and NCO interchangeably,<ref name="latticeSC" /> by convention an NCO refers to the digital (i.e. the discrete-time, discrete amplitude) portion of a DDS<ref>Jane Radatz, The IEEE Standard Dictionary of Electrical and Electronics Terms, IEEE Standards Office, New York, NY, 1997</ref>}} as shown in Figure 1.

The reference oscillator provides a stable time base for the system and determines the frequency accuracy of the DDS. It provides the clock to the ''NCO'', which produces at its output a discrete-time, [[Quantization (signal processing)|quantized]] version of the desired output waveform (often a [[Sine wave|sinusoid]]) whose period is controlled by the digital word contained in the ''Frequency Control Register''. The sampled, digital waveform is converted to an analog waveform by the ''DAC''. The output reconstruction filter rejects the spectral replicas produced by the [[zero-order hold]] inherent in the analog conversion process.