Electronic – pseudo-open-drain-logic


DDR4 reportedly uses something called pseudo-open-drain-logic or PODL. How does it work?

Best Answer

Perhaps I can add a little simple information. As I understand it, POD (Pseudo Open Drain) drivers, have a strong pulldown strength but a weak pullup strength. A pure open-drain driver, by comparison, has no pullup strength except for leakage current; this is why the term "pseudo" is used. The remaining pullup strength is provided by parallel-terminating the receiver at the far end to the HIGH voltage, often using a switchable, on-die terminator instead of a separate resistor. The purpose of all this is to reduce the overall power demand compared to using both strong pullup and strong pulldown, as in drivers such as HSTL. DDR4 memory uses POD drivers, replacing push-pull drivers in DDR3 that drove strongly in both High and Low states.