Subversion Repositories sigma_delta_dac_dual_loop

This project implements 2nd order DAC implementable in FPGA.
The converter generates 1-bit digital signal on the dout output.
You need to connect a simple RC lowpass filter to convert it into
the analog signal.

There are two implementations:
dsm2 - allows to obtain higher clock frequency, and therefore 
       higher oversampling ratio, but number of rising and falling
       slopes in time unit depends on signal value. Therefore
       you may experience nonlinear distortions if those two slopes
       are not symmetrical.
dsm3 - The output of the DAC is updated once every three clock pulses.
       If there is a '1' on the DAC output, the sequence '110' is generated
       on the dout output. If there is a '0' on the DAC output, the sequence
       '100' is generated. Therefore we always have one rising slope and one 
       falling slope generated in each DAC cycle.
       Unfortunately this implementation accepts lower clock frequencies,
       so the oversampling ratio is lower

To check DAC performance without putting it into real hardware, you can
run "make" command in the appropriate directory (it requires free tools:
ghdl, python and pylab). You'll see the spectra of the output signal 
(before low pass filtering) consisting of three sinusoids.