Open drain意思

"Open drain" is a term used in electronics, specifically in the context of CMOS (Complementary Metal-Oxide Semiconductor) logic circuits, to describe a type of output structure where the output transistor is left in a high-impedance state (i.e., neither fully on nor fully off) when the output is not actively driven by the circuit.

In an open-drain configuration, the output transistor is an N-type MOSFET (NMOS) that is turned on when the output is set to a logical low. When the NMOS is on, it can pull the output voltage down to ground (or a low logic level). However, when the output is set to a logical high, the NMOS is not actively driven, and the output is left in a high-impedance state, allowing the output voltage to float to the positive supply voltage (VCC) through a pull-up resistor.

The advantage of an open-drain output is that it can be used in circuits where multiple devices need to share an output line without causing contention. Since the output is in a high-impedance state when not actively driven low, other devices can drive the same line without interference. This is particularly useful in systems that use a common bus or in applications where multiple devices need to communicate with each other over the same line.

In summary, an open-drain output is a type of output configuration where the output transistor is left in a high-impedance state when not actively driven, allowing the output voltage to float to the positive supply voltage through a pull-up resistor. This configuration is useful for sharing output lines among multiple devices without causing conflicts.