What is a Differential Line Driver Output?/What is an Open Collector Output?！

A differential output refers to the fact that each channel has a complement channel, i.e. Channel A and Channel A not. A differential line driver is used to help increase noise immunity (see What are the A not and B not Channels used for?). A differential line driver also allows you to sink or source more current then a Totem Pole output. A differential line driver will work both with a sinking or sourcing circuit. (see What is a Sinking or Sourcing input?) It can also help in increasing the distance in which a signal is transmitted.

An Open Collector output is a NPN transistor. A NPN transistor allows the sinking of current to common. It can be thought of as a switch that allows the circuit, after the load, to be connected to common. This means that a source is required for the output to work. A supply through a load must be connected to the output, otherwise the NPN transistor is simply creating a path to common, i.e. a dry contact. Therefore, if you were to measure the voltage at the output of an open collector that is not hooked up to some supply you would not see a change in voltage. The voltage should be measured across the output load to determine if the open collector is working properly.

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