I have funished AD1955 DAC but I want to modified existing i/v stage that is Op Amp to be mosfet i/v stage.I am so interest Pass D1 i/v stage but there's so many complicate for me to understand ie. Vref ,Sinked current R .My question is ,What should I do , If I replace the Op amp i/v stage by using Pass D1 i/v stage.