Status: Work in Progress
La Ola is a project aimed at creating a fully optimized DDS (Direct Digital Synthesis) implemented in the Amaranth HDL. The goal is to teach myself more Amaranth and tapeout with Skywater or IHP PDKS
Direct Digital Synthesis (DDS) is a technique used to generate precise waveforms digitally.
The observation upon which the direct digital synthesis algorithm is based is that a variable overflowing is isomorphic to one rotation of a phasor. Recall from some math class years ago that a sine wave is generated by projecting a rotating phasor onto the imaginary axis....
The DDS Algorithm: Each time the interrupt fires, it will rotate the phasor to a new orientation, lookup the value for the sine wave at that phasor angle (from a lookup table), and send that value to the DAC. Because of the isomorphism between the accumulator variable and the phasor angle, rotating the phasor is the same as adding an increment to the accumulator variable. The faster that you increment the accumulator variable, the faster the phasor moves around the circle and the higher-frequency the sine wave. The value of the increment and the frequency of the sine wave are, in fact, linearly related. It is not difficult to find that relationship....
Source: Cornell University ECE 4760: Direct Digital Synthesis (DDS)
- Optimized Performance: Built for efficiency in the Amaranth HDL.
- Flexible Design: A modular structure that can be adapted for different frequencies and applications.
- High Precision: Ensures accurate waveform generation for professional-grade digital synthesis.
- Basic implementation
- Simulation
- Add sine quadrant optimizations
- Add interpolation
- FPGA testing
- Integrate with OpenLane
- Send to TinyTapeout
Explore more about DDS and similar projects in these resources:
- Introduction to DDS by Cornell University
- Harmon Instruments Sine/Cosine Core
- Harmon Instruments Open HDL on GitLab
Contributions and suggestions are welcome as we work towards completing this project.