Digital PLL Trigger Control for Low-Jitter CT Imaging
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Solution Overview
Problem
Conventional CT imaging systems face limitations due to slow response times of analog phase locked loops (PLLs) to input frequency variations, leading to output signal jitter and restricted rotational speed changes, which can cause scan aborts and limit diagnostic image reconstruction capabilities.
Innovation Solution
A digital phase locked loop (DPLL) system that pre-sets and locks to a desired frequency, filters output signals to minimize jitter, and interpolates triggers in real-time to maintain stability during errors, allowing for arbitrary trigger specification per gantry rotation and continuous scanning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analog phase locked loop is used to filter output signals, then output signal jitter is reduced, but the response time to input frequency variations becomes slow
Solution Approach 1:
The patent replaces the analog phase locked loop with a digital phase locked loop implementation. The digital PLL uses digital filtering and processing instead of analog circuitry, enabling faster response to encoder frequency variations while maintaining output signal stability. The digital architecture allows for programmable filter characteristics and rapid adaptation to changing input conditions.
Solution Approach 2:
The patent implements dynamic triggering where the number of triggers per gantry rotation can be arbitrarily specified and changed during operation. The digital PLL dynamically adjusts its operation based on real-time encoder feedback, allowing the system to adapt to varying rotational speeds and trigger requirements without the limitations of fixed analog circuitry.
2Device complexity
If the number of output pulses per gantry rotation is limited to predefined values, then system complexity is reduced, but adaptability to different imaging requirements is limited
Solution Approach 1:
The patent enables arbitrary specification of the number of triggers per gantry rotation by changing the digital parameters in the PLL. Instead of being constrained to fixed values determined by hardware dividers, the system allows any integer value to be programmed, providing flexibility for different imaging protocols while maintaining simple operation through software configuration.
3Reliability
If communication errors occur between the encoder and PLL, then scan stability is compromised, but error detection capability is improved
Solution Approach 1:
The patent implements a feedback mechanism where the digital PLL continuously monitors encoder pulses and detects communication errors. When errors are detected, the system can interpolate missing trigger signals based on the expected timing pattern, allowing the scan to continue without interruption while maintaining accurate synchronization.
Solution Approach 2:
The system prepares for potential communication errors by having the digital PLL ready to interpolate missing trigger signals. This preemptive approach ensures that if encoder pulses are lost or corrupted, the system can recover and maintain scan continuity without requiring manual intervention or scan abort.
Data Source
AI summary
A method and apparatus are provided for minimizing output pulse jitters in a phase locked loop. The method includes pre-setting the digital phase locked loop to a desired frequency, locking the digital phase locked loop to the desired frequency to generate an output signal, and filtering the output signal of the digital phase locked loop to maintain undesirable jitter to an acceptable range. In one embodiment, the apparatus is a medical imaging device. In another embodiment, the apparatus is a baggage imaging device.