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How to choose the right circuit output singal of the encoder?

How to choose the right circuit output singal of the encoder?

2020-09-28

It's very important to select the right output signal when you are going to order a rotary encoder.

but how to choose and what's the difference between each signal, here are some introductions might be useful.

As we all known, suppliers always provide following signal output for you, you only need to pick one.

which are:

Push-Pull (HTL)

RS422(TTL)

NPN(Open collector output)

PNP output

Voltage output


A) Push-Pull Signal Output (HTL)

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 5 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

B) RS422 Signal Output (TTL)

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 3.5 to 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 (200KHZ or 400KHZ)and the best noise immunity f or a higher motor turning speed.

To ensure this the receiver should also be a differential.


1) PNP open collector (Current source)


2) NPN open collector (Current Sink)


Voltage Output Levels:

A logic gate interprets certain input voltages as high (logic 1) or low (logic 0).

TTL (transistor-transistor-logic): A signal above 2 V is interpreted as logic 1 and a signal less than 0.8 V is interpreted as logic 0. The output voltage ranges between 0-5 V.

HTL (high-threshold-logic): A signal above 3 V is a logic 1 and a signal less than 1 V is a logic 0. The high output signal level is dependent from the supply voltage.

Because of the higher voltage difference between logic 0 and 1, the HTL logic is more immune to interference and more resistant against electrical noise.

LogicSignal LevelSupply VoltageOutput Voltage
TTLHigh4.75-30 Vmin 3 V

Low4.75-30 Vmax 0.5 V




HTLHigh4.75-9 Vmin 3 V


9-30 Vmin Supply Voltage - 3 V

Low4.75-30 Vmax 0.5 V


Above offers some simple graph of each type of encoder output signal,

if you still have any doubt on this, you may contact our technician to get more assistant.


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