Terminating differential encoder lines

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Differential encoders (the ones which have complementary output pairs, such as quadrature outputs A+, A-, B+ and B-) are typically designed to be driven into RS422 type differential receiver circuit. Such circuit is present in most Granite Devices drives, such as ARGON and IONI.

Line termination can be used to enhance signal quality and reliability in the differential line. Termination means adding a resistor between the differential pair wires at the end of cable. Resistance value should match the cable characteristic impedance. If not impedance is not known, safe assumption is to use 100 to 120 ohm resistors.

Incremental encoders[edit | edit source]


Encoder differential line termination with resistors

Serial data encoders (SSI/BiSS)[edit | edit source]

Ssi biss wiring termination large.svg

SSI/BiSS encoder with differential clock and data lines with

Is termination necessary?[edit | edit source]

If encoder cable is long, then termination may be required for stable readout of encoder. As rule of thumb, normally quadrature encoder cables shorter than 3 meters don't need termination. This might be different for serial data encoders, such as BiSS or SSI encoders because they usually carry higher frequency signals. However, if signal quality problems occur, then it is always advised to try termination as well as use of EMI suppression cores.

For calculations for termination necessity in general cases, see: http://ltxfaq.custhelp.com/app/answers/detail/a_id/1382/~/rs485-%26-rs422---when-is-termination-required%3F

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