Direct Digital Synthesis

• Direct synthesis has several advantages including fast settling, fine step sizes, and simple implementation.

  • A digital accumulator accessing a sine ROM look-up table drives a digital-to-analog converter (DAC).

• Direct synthesis has several disadvantages

  • Bandwidth is limited to fclock/4, due to folding of spurious frequencies
  • High bandwidth requires a high speed process and high DC power
  • Spurious performance typically is dominated by the DAC
    • Ideal DAC spur free dynamic range is 9 dB × no. of linear DAC bits
    • Achieving good DAC linearity at high speed is challenging

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