Charge Rebalanced Integrator for CT Imaging Noise Reduction
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Solution Overview
Problem
In CT imaging systems, the integration capacitor in the integrator circuit faces challenges in maintaining signal quality due to noise interference, particularly when dealing with high dynamic range signals, as larger capacitors are required to handle increased X-ray intensity, leading to reduced gain and increased backend noise.
Innovation Solution
Implementing a charge rebalancing technique that monitors the integrator circuit's output voltage and adjusts it within a specified range using a conditional charge transfer circuit, allowing for multiple rebalancing events during a single integration period without resetting the integration capacitor, thereby reducing noise dependency on full-scale range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the integration capacitor size is increased to handle high X-ray intensity, then the dynamic range is improved, but the gain is reduced and backend noise increases
Solution Approach 1:
The patent applies periodic charge transfer actions during the integration period to rebalance the integrator output voltage. By periodically transferring charge from the input node to ground when the output voltage exceeds threshold levels, the system maintains the integrator within the optimal input range of the ADC, enabling the use of larger integration capacitors for high dynamic range without suffering from increased backend noise, as the capacitor size is no longer constrained by the need to maintain voltage within range
2Measurement precision
If the integration capacitor is reset frequently to maintain voltage range, then the signal quality is improved, but the noise dependency on full-scale range increases
Solution Approach 1:
The patent implements preliminary charge transfer action by monitoring the integrator output voltage and transferring charge proactively when the voltage approaches threshold levels, before the integrator goes out of range. This preventive approach maintains signal quality throughout the integration period without requiring frequent resets, thereby reducing noise dependency on full-scale range while maintaining measurement precision
Data Source
AI summary
A charge rebalancing integration circuit can help keep an output node of a front-end integration circuit within a specified range, e.g., without requiring resetting of the integration capacitor. The process of monitoring and rebalancing the integration circuit can operate on a much shorter time base than the integration time period, which can allow for multiple charge balancing charge transfer events during the integration time period, and sampling of the integration capacitor once per integration time period, such as at the end of that integration time period. Information about the charge rebalancing can be used to adjust subsequent discrete-time signal processing, such as digitized values of the samples. Improved dynamic range and noise performance is possible. Computed tomography (CT) imaging and other use cases are described, including those with variable integration periods.