Understanding Totem Pole Encoder Circuits for Your Applications

When selecting an incremental encoder, it's crucial to determine the type of output required to ensure compatibility with the receiving device. One popular choice is the Totem pole encoder circuit, which is commonly used in applications with short cable lengths and requires 12V or 24V level signals.

Open Collector NPN vs. TTL/HTL

In open collector configuration, a signal is typically more susceptible to electrical noise than TTL (Transistor Transistor Logic) or HTL (High Threshold Logic). When activated, the signal is pulled low, while when inactive, it's pulled to supply common. On the other hand, TTL and HTL provide excellent noise immunity and faster signal response.

Totem Pole Configuration

The Totem pole circuit uses two transistors in a specific configuration to generate output channels, ensuring that the signal remains high or low. This design provides current flow in both directions, making it suitable for applications with short cable lengths.

RS422 Differential Outputs

Incremental encoders often feature RS422 differential outputs, which provide excellent noise immunity and fast signal response. These outputs allow for the use of long cable lengths without compromising signal quality. The output voltage level is either 0 volts in a low state or 5 volts in a high state, regardless of the supply voltage level.

TTL vs. HTL

TTL provides an RS422 output signal level that is +5VDC when active, whereas HTL offers balanced differential line driver outputs. Choosing the wrong output type can result in a non-functional system and potential hardware damage.

Understanding Incremental Encoder Outputs

Incremental encoders are commonly used in industries such as packaging, printing, conveyors, and converting for speed and velocity control. They typically produce square or sine/cosine wave outputs that are transmitted to a control unit for each rotation. The position is defined by the number of pulses per rotation.

Absolute vs. Incremental Encoders

In contrast to absolute encoders, incremental encoders provide relative position information by counting the pulses with output data. They are generally used in applications where controlling and monitoring exact position is crucial, such as transport logistics, robotics, and other industries.

By understanding the differences between Totem pole encoder circuits, TTL, HTL, and RS422 outputs, you can select the right encoder for your application and ensure compatibility with your receiving device.