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Furthermore, the continual improvements in both process technology and design have resulted in cost and power consumption levels that were previously unthinkably low.For example, the AD9833, a DDS-based programmable waveform generator (Figure 1), operating at 5.5 V with a 25-MHz clock, consumes a maximum power of 30 (SPI), and need only an external clock to generate simple sine waves.By continuing to use this site, you consent to the use of cookies.

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The number of discrete phase points contained in the value is changed to 0111...1111, the phase accumulator will overflow after only 2 reference-clock cycles (the minimum required by Nyquist).

This relationship is found in the basic tuning equation for DDS architecture: changes in the output frequency.

DDS devices are not limited to purely sinusoidal outputs.

Figure 2 shows the square-, triangular-, and sinusoidal outputs available from an AD9833. The binary number in the frequency register provides the main input to the phase accumulator.

Since sampling theory dictates that at least two samples per cycle are required to reconstruct the output waveform, the maximum fundamental output frequency of a DDS is /2.

However, for practical applications, the output frequency is limited to somewhat less than that, improving the quality of the reconstructed waveform and permitting filtering on the output.Each designated point on the phase wheel corresponds to the equivalent point on a cycle of a sine wave.As the vector rotates around the wheel, visualize that the sine of the angle generates a corresponding output sine wave.If a sine look-up table is used, the phase accumulator computes a phase (angle) address for the look-up table, which outputs the digital value of amplitude—corresponding to the sine of that phase angle—to the DAC.The DAC, in turn, converts that number to a corresponding value of analog voltage or current.No loop settling time is incurred as in the case of a phase-locked loop.As the output frequency is increased, the number of samples per cycle decreases.To learn more or modify/prevent the use of cookies, see our Cookie Policy and Privacy Policy.(DDS) is a method of producing an analog waveform—usually a sine wave—by generating a time-varying signal in digital form and then performing a digital-to-analog conversion.If the phase increment is small, the phase accumulator will take many more steps, accordingly generating a slower waveform.The integration of a D/A converter and a DDS onto a single chip is commonly known as a complete DDS solution, a property common to all DDS devices from ADI.


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