PLL Sample Clocking for OCT Noise and Phase Jitter Control
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Solution Overview
Problem
Optical coherence tomography (OCT) systems face challenges in synchronizing data collection with the changing optical frequency of tunable light sources, leading to noise, jitter, and other undesirable effects due to the limitations of conventional clock generators.
Innovation Solution
The use of phase-locked loops (PLLs) with wide-bandwidth voltage-controlled oscillators (VCOs) and noise compensating subsystems to generate a stable clock signal for OCT systems, enabling efficient synchronization and reducing noise and phase jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional clock generators are used to synchronize data collection with the changing optical frequency of tunable light sources, then the system can operate with simple clocking mechanisms, but noise and phase jitter increase leading to degraded OCT image quality
Solution Approach 1:
The patent employs a phase-locked loop (PLL) that continuously monitors the phase difference between the clock signal and the optical frequency signal, and adjusts the clock signal frequency in real-time to maintain synchronization. This feedback mechanism eliminates noise and phase jitter by dynamically correcting deviations, thereby improving synchronization accuracy without compromising signal quality.
Solution Approach 2:
The patent introduces an intermediary PLL circuit that acts as a buffer between the tunable light source and the data collection system. This intermediary processes and condition the clock signal, filtering out noise and phase jitter before the signal reaches the data acquisition system, thus protecting the overall system from harmful fluctuations.
2Measurement precision
If the optical frequency of the tunable light source is swept over a range of wavelengths to improve OCT imaging capability, then data acquisition quality improves, but synchronization complexity increases
Solution Approach 1:
The patent replaces complex mechanical synchronization mechanisms with an electronic PLL-based system. The PLL uses electronic feedback control to synchronize the clock signal with the optical frequency sweep, eliminating the need for complex mechanical linkages or manual calibration systems while maintaining high synchronization precision required for improved OCT imaging resolution.
3Speed
If fast turn-on characteristics are required for the clock generator to meet discontinuous operation requirements, then system response time improves, but phase locking stability deteriorates
Solution Approach 1:
The patent implements a dynamic PLL system with adjustable loop bandwidth that can adapt its response characteristics based on operational requirements. During fast turn-on, the loop bandwidth is widened to allow rapid frequency acquisition and locking. Once locked, the bandwidth is narrowed to enhance phase lock stability and reduce jitter, thus achieving both fast response and stable operation.
Solution Approach 2:
The patent employs preliminary frequency estimation and coarse locking mechanisms that prepare the PLL for fast acquisition before fine tuning begins. By pre-positioning the VCO frequency close to the target frequency and establishing initial phase relationships, the system achieves rapid lock-on without sacrificing subsequent stability during the fine-tuning phase.
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
This approach effectively reduces noise and phase jitter, improving the resolution and dynamic range of OCT systems by generating a sample clock that is synchronized with the optical frequency of the tunable light source, thereby enhancing data acquisition in OCT systems.
Implementation Method 1
frequency multiplying the first clock signal or a signal derived therefrom by N using an oscillator to generate a clock signal
Implementation Method 2
wide-bandwidth voltage-controlled oscillators (VCOs)
Data Source
AI summary
In part, the invention relates to an optical coherence tomography system that includes one or more phased-locked loop circuits. In one embodiment, the phased-locked loop circuit includes a phase detector, a loop filter, and a voltage controlled oscillator wherein the phased-locked loop circuit is configured to generate a sample clock. The optical coherence tomography system can include an analog to digital converter having a sample clock input, an interferometric signal input, and a sample data output, the analog to digital converter configured to receive the sample clock and sample OCT data in response thereto. In one embodiment, the phased-locked loop circuit is configured to lock on a first signal in less than or equal to about 1 microseconds.