Today most incremental encoders have a Push-Pull (HTL) or RS422 (TTL) output driver, these have replaced most of the older output circuits like Open Collector NPN, Open Collector PNP, Voltage Output.
Push-Pull (HTL) circuits, also known as Totem Pole, provide a signal level which corresponds to the applied supply voltage. The supply voltage typically ranges from 8 to 30 VDC.
With proper connections you can use the Push Pull interface to replace true open collector circuits by using an external diode connected in a way to limit the direction of the current for RS422 (TTL) circuits provide a constant 5 V signal level that is not dependent on the supply voltage. Two supply voltage ranges can be selected: From 4.75 to 5.5 VDC (can be used to replace open collector output drivers) or from 8 to 30 VDC. Using differential signals the output fully complies to the RS422 standard.
The differential outputs have the highest frequency response capability and the best noise immunity. To ensure this the receiver should also be a differential.