Optical Gyroscope Drive Signal Resolution via Dither Noise
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Solution Overview
Problem
Conventional interferometric fiber optic gyros (IFOGs) face reduced sensitivity at low rotation rates and near zero degrees phase detection, leading to 'deadband' errors due to digital signal truncation and slow convergence of loop errors, which can be exacerbated by vibrations.
Innovation Solution
A system for driving a sensing coil in an optical gyro that includes a photodetection circuit producing a digital signal, a signal processing circuit adding a random number to the feedback signal to increase resolution, and a digital-to-analog converter with a lower resolution, which reduces deadband and quantization noise by enhancing the resolution of the drive signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If digital signals from servo electronics are truncated to lower bit values prior to supplying to DAC, then device complexity is reduced, but measurement precision deteriorates due to deadband errors
Solution Approach 1:
The patent applies preliminary action by adding dither noise to the digital feedback signal before it is truncated and converted to analog. This pre-processing step ensures that the signal contains sufficient information to overcome the limitations of subsequent truncation, thereby maintaining measurement precision while allowing for simpler downstream processing.
Solution Approach 2:
The patent introduces dither noise as an intermediary element between the digital feedback signal and the truncation process. This intermediary adds random variations that prevent signal components from consistently falling into the same quantization bins, thereby reducing deadband errors and preserving measurement accuracy despite the subsequent reduction in signal resolution.
2Device complexity
If truncation of digital signals is applied, then device complexity is reduced, but reliability deteriorates due to asymmetry that rectifies into rate error under vibration
Solution Approach 1:
The patent applies preliminary action by adding dither noise to the digital feedback signal before truncation. This pre-processing step randomizes the quantization errors that would otherwise create asymmetric patterns under vibration, thereby preventing the rectification of rate errors and maintaining measurement reliability.
Solution Approach 2:
The patent converts the potentially harmful effect of truncation-induced asymmetry into a beneficial outcome. By adding dither noise, the systematic asymmetric errors are transformed into random noise that can be averaged out, thereby converting a reliability-degrading effect into one that maintains measurement accuracy even under vibrational conditions.
3Device complexity
If truncation of digital signals is applied, then device complexity is reduced, but loss of time increases due to extended convergence time of loop error
Solution Approach 1:
The patent applies preliminary action by adding dither noise to the digital feedback signal before truncation. This pre-processing step accelerates the convergence of loop errors by preventing the signal from becoming stuck in local minima caused by quantization, thereby reducing the time required for the system to reach steady-state operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The addition of random noise to the feedback signal increases the resolution of the drive signal, reducing deadband errors and quantization noise, thereby improving the sensitivity and accuracy of rotation rate detection in optical gyros.
Implementation Method 1
a photodetection circuit with an input for receiving an optical output from the sensing coil and having an output, said photodetection circuit producing a digital signal from said optical output
Implementation Method 2
The two counter-propagating (e.g., CW and CCW) beams experience different optical pathlengths while propagating around a rotating closed optical path or loop. For example, rotation about the sensing axis increases the optical path length in one rotational direction and decreases the optical path length in the other rotation direction. The difference in the two optical pathlengths introduces a phase shift between the light beams for either rotation direction (i.e., the Sagnac effect)
Data Source
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AI summary
Methods and system are provided for driving light through a sensing coil of an optical gyro. The system includes a photodetection circuit (32) having an input for receiving an optical output from the sensing coil and having an output, and a signal processing circuit (50) having an input coupled to the output of the photodetection circuit (32) and having an output for supplying an output signal to modulate the sensing coil. The photodetection system (32) produces a digital signal from the optical output. The signal processing circuit (50) produces a feedback signal from the digital signal and adds a random number to the feedback signal to produce the output signal.