DAC output

Digitizer DAC output

The digitizer has a fast, but low resolution (10 bit) DAC. The DAC output is driven psuedo-differentially out two connectors on the front panel. One output is the plus side, one the minus side. The DAC is noisy and is not suitable for seeing fine detail. There is a ton of 100MHz clock pickup from the board's oscillator. The DAC is only usable if you bandwidth-limit the scope probe to 20MHz. For most applications you also want to average traces if at all possible.

DAC functionality in latest version of firmware

The 20180607 firmware release for the digitizer (SVN index #4830) was compiled with the command-line options of "SLAVE_MODE=0, DIAG_MUX_SIZE=0, INCLUDE_DSP_ILA=0, INCLUDE_LVME_ILA=0". The DIAG_MUX_SIZE=0 option disables the DAC by setting the data sent to the DAC to be a constant zero; the compiler then optimizes out all possible DAC choices.

Optional firmware choices

Test builds are being generated 20181212 with different DAC options.

• A build with DIAG_MUX_SIZE=2 provides a two-level mux that allows you to get the waveform from a couple different points in the delay chain, from any channel, with variable gain. Compile in progress.