Optical Encoder Signal Conditioning for Stable Sinusoidal Amplitude
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Solution Overview
Problem
Conventional open-loop optical motion encoders face limitations such as device aging, temperature drifts, and contamination, which conventional solutions like binning, device trimming, or signal conditioning feedback systems fail to adequately address, especially in high-resolution applications requiring interpolation of 10× to 1000×, due to increased complexity, cost, and sensitivity to process variations.
Innovation Solution
An optical encoder with a signal conditioning system that includes a peak comparator, pulse generator, threshold comparator, and digital circuitry to adjust the emitter drive signal by comparing input sinusoidal signals over time, modifying the emitter current to maintain consistent differential signal amplitude within a defined window, thereby compensating for variations caused by aging and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional binning options, device trimming, or firmware calibrations are used to compensate for device aging and temperature drifts, then measurement precision is improved, but device complexity and die size increase
Solution Approach 1:
The encoder performs self-calibration by continuously monitoring its own output signals and automatically adjusting the emitter drive current to maintain signal amplitude within a target window, eliminating the need for external binning options, device trimming, or firmware calibrations
Solution Approach 2:
A feedback mechanism compares the actual differential signal amplitude with a target amplitude window and dynamically adjusts the emitter drive signal accordingly, enabling real-time compensation for device aging and temperature drifts without increasing device complexity
2Measurement precision
If conventional signal conditioning feedback systems with low pass filters are used to extract DC component, then measurement precision is improved, but device complexity and cost increase due to big passive capacitors or active filters
Solution Approach 1:
The patent replaces the conventional mechanical/electrical low pass filter system with a digital signal processing approach that uses peak detection and comparison circuits to extract the DC component and determine signal amplitude, eliminating the need for big passive capacitors or active filters
Solution Approach 2:
The system changes the approach from frequency-domain filtering to time-domain peak comparison, where the peak comparator detects peaks by comparing current signal levels with previous levels, and the signal amplitude is determined by comparing peak values, thereby avoiding complex filter hardware
3Device complexity
If conventional signal conditioning feedback systems are implemented without device trimming, then device complexity is reduced, but measurement precision deteriorates due to sensitivity to process variations
Solution Approach 1:
The system automatically compensates for process variations through self-calibration by monitoring its own output signals and adjusting the emitter drive current to maintain signal amplitude within the target window, eliminating the need for external trimming while maintaining precision
Solution Approach 2:
A feedback loop continuously monitors the differential signal amplitude and dynamically adjusts the emitter drive signal to keep the amplitude within the target window, providing immunity to process variations without requiring device trimming
Data Source
AI summary
An encoder with signal conditioning of an emitter drive signal is described. In one embodiment, the encoder includes a peak comparator, a pulse generator, a threshold comparator, and digital circuitry. The peak comparator outputs a peak comparator signal based on a comparison of an input sinusoidal signal stored at a first time with the input sinusoidal signal stored at a second time. The pulse generator determines a peak of the input sinusoidal signal based on the peak comparator signal. The threshold comparator compares a differential signal amplitude with a differential signal amplitude window at approximately the peak of the input sinusoidal signal. The differential signal amplitude is associated with the input sinusoidal signal. The digital circuitry generates an emitter modification signal in response to a determination that the differential signal amplitude is outside of the differential signal amplitude window.