This Wisamic encoder [english
page] has NPN outputs so you need pullup resistors connected to both output pins.
Here is diagram of a similar OMRON encoder:
View attachment 28855
Those pullups [e.g. 1K] can be connected to 3V3 and than the output signals are safe for any Teensy.
Yes, exactly. All that is needed is a pull-up resistor to 3.3V per output.
This is an "open collector" output, so named because the output is the collector from an NPN transistor (which is not connected to anywhere else).
The exact value of the pullup is not very important. At 3.3V, a 1kOhm resistor means the NPN transistor needs to sink 3.3V/1000Ohm=3.3mA, which is a tenth of the maximum (35mA) shown in the diagram. It is a strong pullup, making sure the output gets decisively high. This is good, especially if the microcontroller is not immediately next to the encoder, and you have a bit of wire in between.
If this was a battery-operated circuit, then one might save a tiny bit of power by using a weaker pull-up, maybe 2.2kOhm, 4.7kOhm, or 10kOhm.
I normally default to weaker pullups, starting at 10k, and then adjust based on what I see. With longer wires, I use stronger pull-ups.
Even though I like to simulate my circuits, I always do final adjustments based on practical measurements and observations.
In another thread I
showed a circuit that can be used if the encoder output is not an open collector or open drain one. With this output, an open collector output, there is absolutely no need to use such a circuit: any additional circuitry won't make it work any better. Basically, what that circuit of mine does, is turn any output into an open collector one, using N-channel enhancement mode MOSFETs that can handle ±20V input signals, with an added inrush current limiting resistor for the MOSFET switching.