DDS Arbitrary Waveform Output Based on FPGA

Use verilog to implement

The principle of DDS
DDS (Direct Digital Frequency Synthesizer) direct digital frequency synthesizer, also called DDFS.
•DDS is a frequency synthesis technique that directly synthesizes the desired waveform from the concept of phase.
• Not only can generate sine waves of different frequencies, but also control the initial phase of the waveform.
DDS block diagram

Main components:
Internal: phase accumulator, sine look-up table
Peripheral: DAC, LPF (low-pass filter)
Working process
1. Digital waveform to be stored in ROM, through the DAC, the analog waveform is formed.
2. Change the addressing step to change the frequency of the output signal.The step size is the phase increment for the digital waveform lookup table.The phase increment is accumulated by the accumulator, and the value of the accumulator is used as the address of the look-up table.
3. The stepped waveform output by the DAC becomes an analog waveform after low-pass filtering.
Frequency Control

In the program, the sampling clock is 50M, the bit width of the N-phase accumulator is 32, and the bit width of the M frequency control word is 16 bits;
The maximum frequency that can be controlled is 65535*50000000/4294967296=762Hz;

Phase Control

Waveform storage
Corresponding relationship between phase and amplitude of sinusoidal signal