I wonder if it is possible to use the DAC in STM32G4 to produce a 30kHz sinewave with 1Hz resolution.

[GGold.3]

The application is to fine tune acoustic resonantors. In other words we want to be able to tune DMA DAC output from 29.990 to 30.010 in 1 Hz steps. Ideally we also would like to tune the amplitude. There are some ideas with DAC reference prescalers and different LUTs. Any idea for a more elegant solution?

[waclawek.jan]

That's what you get with DDS, too - you just change the phase *increment* value, so phase remains continuous.

JW

[AScha.3]

well, question is: do you want/need full sinewave with many samples in constant pattern ?

then, as ...Jan and others explained, not possible.

if you can be ok with an little "noisy" pattern, then DDS is the solution.

because 32bit cpu here, lets take a 32bit dds -> and for good THD, 1024 elements 12 bit (data) value lookup table.

so we calculate a 32bit "phase-accu" , using top 10bits for the lookup table.

and we try calculation at 600kHz , = "sampling frequ." . (if we (cpu) can faster...good. we will see..)

the loop is simple:

// preset array with 1024 sinus values, one full 2pi wave
uint16_t sinval[1024];
 
uint32_t  phase_sum, phase_speed;
phase_speed = 213909504;  // for 29,882 KHz at 600k sampling
while(1 ...loop) // - or better : do in timer INT , called at 600kHz
{
  phase_sum += phase_speed;   // sum just rolls over...for next sine wave :)
  DAC1->DHR12R1 = sinval[phase_sum>>22];  // DAC1->DHR12R1 = mod. -> dac write register
}
 

so resolution is about 0,00011 Hz . (average....and need low pass filter, maybe 40kHz , 12dB/Oct. )

"program" is just to show the way, not without possible error...