(09-10-2020, 03:58 PM)Tim Curtis Wrote: Tell us about the firmware in the Altera and what I2S driver is being used.
This project had been planed for more than a year, I'm not familiar with Linux coding , I ask around on WWW about how to create a custom I2S driver, and I fail to find any clue to do that.
I ended up to program the FPGA to accept basic Generic ( R-Pi DAC) driver.
The Altera is basically a I2S serial to parallel converter, and also a binary to unity counter( thermometer counter ) to correct 4 bit nearest to MSB , and also reduced glitches to -24dB lower than normal R2R DAC. slew rate control in the FPGA further reduced glitches too.
Matching resistors are very time consuming , before matching them , I heat up a batch of 0.1% resistors in oven for 30 minutes and cool it down , and repeat the cycle 3 times. From 0.1%, I have 2 batches of 0.05% sorted, and then from there, I matched down to 0.01 and finally matched down to 0.005% .
