865 NCO
865 : NCO
- Author: Pantelis
- Description: Numerically Controlled Oscillator
- GitHub repository
- Open in 3D viewer
- Clock: 50000000 Hz
How it works
Numerically Controlled Oscillator (NCO) with linear-interpolated sine output.
- 8-bit
freq_ctrlcontrols the output frequency - 8-bit
dac_outdrives a DAC - Uses 16-bit phase accumulator + sine ROM + linear interpolation between samples.
Frequency relationship (with PHASE_WIDTH = 16, ROM_ADDR_BITS = 6)
f_out = (freq_ctrl / 2^PHASE_WIDTH) * f_clk
It's a basic block for Direct Digital Synthesis (DDS).
How to test
On the board connct the uo_out on an 8-bit DAC. The output of the DAC
connected to an oscilloscope should give you a sinewave of controlled frequency
(freq_ctrl needs to be in the range [1, 255]).
Run the bit-accurate python model
You can run the python model to get an idea of the expected output by observing the generated plots:
$ cd python_nco_model
$ python3 nco_model.py
$ eog nco_qwave_waveforms.png
Run Simulation
$ cd sim
$ make waves
You can observe in gtkwave the dac_out output using the analog data format.
External hardware
8-bit DAC connected at the output.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | freq_ctrl_0 | dac_out_0 | |
| 1 | freq_ctrl_1 | dac_out_1 | |
| 2 | freq_ctrl_2 | dac_out_2 | |
| 3 | freq_ctrl_3 | dac_out_3 | |
| 4 | freq_ctrl_4 | dac_out_4 | |
| 5 | freq_ctrl_5 | dac_out_5 | |
| 6 | freq_ctrl_6 | dac_out_6 | |
| 7 | freq_ctrl_7 | dac_out_7 |