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Encoder Signal Flicker: Causes and Troubleshooting Tips

Encoder signal flicker or jump is an inconsistency in encoder pulse shape and can often be mistaken for jitter. Encoder jitter will usually have a pattern of inconsistency while flicker can be seen more prominently by zooming in and out of the pulse wave but occur somewhat randomly.

Most Likely Causes of Encoder Signal Flicker

Interpolation increases the effective resolution of the encoder by interpolating between data points. The technique can be used to double up an 1800 PPR encoder to act as a 3600 PPR encoder, for example. Interpolation assumes that the two pulses are identical in size, frequency, symmetry, and facing. If there is a deviation in symmetry, for example, the trace will jump when the scope triggers on the first pulse.

Quick Troubleshooting Tips

Does the signal appear to be a square wave?
Does it flicker or jump with a specific periodicity?

Diagnosis

For encoders using interpolation, this is part of normal operation. The question to answer is whether the flicker is out of spec and the encoder datasheet should be consulted to determine if the issue is within the operating specification. If the application requires precise signals or detection of trace amounts of motion, an encoder with direct-read true resolution (not interpolated) may be better suited.