Open-drain output buffer

Hi,

May i know what is open-drain output buffer? what is the purpose of using it? I always read it from paper. It always used to match 50ohm instrument load. How it can match to 50ohm?

Thanks.

Open-drain outputs are outputs which at any given time are either actively sinking current (i.e., low voltage, typically considered logic 0) or are high impedance, but which never source current (high voltage, logic 1) ..
Open-drain refers to the drain terminal of a MOS FET transistor ..
The equivalent concept on a bipolar device is called open-collector ..

To "match" it to 50Ω transmission line you will need to connect a 50Ω resistor between open-drain output and Vdd .. see attached picture ..

Regards,
IanP