PLL Circuit Adjusts Optical Measurement Time Window
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Solution Overview
Problem
Current optical measurement systems for detecting neural activity in the brain face challenges in accurately aligning the measurement time window with respect to light pulses, leading to inefficiencies in generating a temporal point spread function (TPSF) and conserving power.
Innovation Solution
The implementation of a phase lock loop (PLL) circuit-based system that adjusts the measurement time window within the light pulse time period, using a precision timing circuit and a measurement time window management circuit to sweep and align the TPSF accurately, ensuring consistent placement and power conservation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a measurement time window is used in optical measurement systems, then neural activity detection can be performed, but accurate alignment of the measurement time window with light pulses is challenging
Solution Approach 1:
A phase lock loop (PLL) circuit is introduced as an intermediary component to synchronize the measurement time window with the light pulse train. The PLL circuit receives a reference signal from the light source and generates a synchronized timing signal that automatically aligns the measurement window with each light pulse, eliminating manual alignment complexity while achieving high precision.
Solution Approach 2:
The PLL circuit implements a feedback mechanism where the phase detector continuously compares the timing of the measurement window with the reference light pulse signal, and the loop filter adjusts the VCO output frequency and phase to maintain accurate synchronization. This closed-loop feedback ensures consistent alignment without requiring complex external control systems.
2Productivity
If the measurement time window is aligned accurately with light pulses, then the temporal point spread function (TPSF) is generated efficiently, but power consumption increases
Solution Approach 1:
The measurement time window is activated periodically in synchronization with the light pulse train through the PLL circuit. Instead of continuous operation, the photodetector and timing circuits are enabled only during brief windows coinciding with light pulse arrivals, achieving efficient TPSF generation while minimizing power consumption during idle periods.
Solution Approach 2:
The PLL circuit performs preliminary synchronization by generating advance timing signals that prepare the measurement system before each light pulse arrives. The measurement window is pre-positioned and activated only when needed, avoiding continuous operation and reducing overall power consumption while maintaining measurement efficiency.
3Loss of energy
If the measurement time window is not consistently aligned with light pulses, then power is conserved, but the TPSF generation becomes inefficient
Solution Approach 1:
The system employs periodic activation of the measurement window synchronized with the light pulse frequency. The PLL circuit ensures the measurement window opens only during the brief periods when light pulses are present, achieving both power conservation through minimal active operation and efficient TPSF generation through consistent temporal alignment.
Data Source
AI summary
An illustrative system may include a TDC configured to monitor for an occurrence of a photodetector output pulse during a measurement time window that is within and shorter in duration than a light pulse time period, the photodetector output pulse generated by a photodetector when the photodetector detects a photon from a light pulse having a light pulse time period; a PLL circuit for the TDC and having a PLL feedback period defined by a reference clock, the PLL circuit configured to: output a plurality of fine phase signals and output one or more signals representative of a plurality of feedback divider states during the PLL feedback period; and a precision timing circuit configured to adjust, based on one or more of the fine phase signals and/or the feedback divider states, a temporal position of the measurement time window within the light pulse time period.