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A linear absolute optical encoder with self-adaptive reference
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DOI：10.1016/j.sna.2026.117771.png)
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Abstract
En 中文
In traditional absolute optical encoders, the DC component of the absolute code analog signal is highly sensitive to environmental factors, which leads to changes in the duty cycle of the output signal and increased signal error rate. This paper introduces an innovative approach for generating a self-adaptive reference based on the collaboration between coding and circuit design, enabling precise absolute code acquisition with lower hardware costs. By leveraging the DC balance characteristic of Manchester coding, an analog averaging topology was constructed by reusing the resistor network of the signal channels. This topology extracts the average DC value of all channel signals as a self-adaptive reference for the comparator, ensuring the duty cycles of the absolute output signals remain stable around the ideal 50%. To verify the effectiveness of the proposed architecture, a linear optical encoder chip including an absolute code track and dual incremental code tracks was designed and fabricated using a 0.18 & micro;m CMOS process. Testing results show that at a nominal LED current of 5.75 mA, the duty cycle error of absolute signals remains within +/- 5.74%. When the LED current varies between 3.25 mA and 8.25 mA, the fluctuation range of the signal duty cycle is 5.3% with the proposed method, while a fixed reference results in a fluctuation of 43.2%. Featuring low hardware overhead, the proposed method provides an efficient solution for high-precision encoder systems in complex industrial environments.
Keywords:
Linear optical encoder
Manchester coding
Self-adaptive reference
CMOS integrated circuit
M-sequence
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