direct digital synthesis (oscillator) (DDS)

Direct digital synthesis( DDS) is a method for the precise generation of frequencies. Before frequencies are generated with the DDS method, the period of a sinusoidal signal is quantized with high temporal and amplitude resolution. The quantized data is stored in the memory of the microcomputer and cannot be changed.

To generate a frequency, the values are read out one after the other in a clock-controlled manner. If all values are read out, the frequency of the previously stored sine wave is obtained. If only every second value is read out, the period is halved and the frequency is doubled. Thus, with sufficiently high temporal resolution, higher frequencies can be generated with high accuracy by omitting data values. Lower frequencies are obtained by adding data values. For example, if every fifth data word is used twice, the period increases by 20% and the frequency drops by the corresponding value.

Direct digital synthesis (DDS) using the example of frequency doubling

The consecutive clock-controlled data values are converted into an analog step-shaped signal in a D/A converter before it is formed into a sinusoidal signal in a filter. The accuracy of the generated frequency depends on the accuracy of the clock signal and the resolution of the quantized sine wave.

Direct digital synthesis is used in precision generators, in RF gener ators and function generators. The technology is characterized by extremely fine frequency tuning down to the millihertz range as well as fast frequency and phase changes. In addition, Direct DigitalSynthesizers (DDS), also known as Numerically Controlled Oscillators( NCO) or Digitally Controlled Oscillators( DCO), have high frequency stability and low phase noise.