• on Test & Measurement
  • Published in issue 3/2009 on page 38
About the article

Sinewaves in Programmable Logic

Direct digital synthesis using an Altera CPLD

Sinewaves in Programmable Logic
Generating a stable, high-frequency signal from a crystal is simple, but you can’t always get just the frequency you want. Of course, you can always order custom-made crystals, but not everyone can afford this and it’s not necessarily terribly practical. A more flexible solution is direct digital synthesis (DDS). Ready-made DDS devices do exist, but are complicated to use. Here’s a compromise between the flexibility of a DDS device and the inflexibility of a crystal: programmable logic.
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Technical specifications
- DDS frequency synthesizer (Direct Digital Synthesizer)
- Sinewave output by virtue of the principle and the filtering
- Output frequency from 610 Hz to 28 MHz with a resolution of 610 Hz
- Possibility of performing FSK (Frequency Shift Keying) frequency modulation.
- EPM7064SLC44 10 (or LC44 7) programmable logic IC from Altera
- 70 MHz operating frequency
- R-2R network DAC
- Output filtering using an LC circuit
- 5 V supply
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