Is there a current DAC which has 0 current (< 1 nA) for an input code of 0? I am driving an LED, so would it make sense to use bipolar supply rails (where a negative output would reverse bias the LED and give 0 current)? For my project the current error must be less than 1 uA and the FSR need only be greater than 200 uA. My current design uses an 8750 from ti, which has too high of offset current (0.01% of FSR = 2 uA).
I used a 100 uA current source in parallel with the LED (REF200 from ti), and now am getting pA of zero-scale current (the threshold voltage of the LED is greater than the output/saturation voltage of the current source (REF200)).