Photon Counting Noise Shaping With Event-Triggered ADC Gating
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Solution Overview
Problem
Conventional photon counting systems in medical imaging, such as CT systems, consume excessive power due to the need for high bandwidth amplifiers to process spectral information, leading to inefficiencies and increased noise.
Innovation Solution
A circuit comprising a charge sensitive amplifier, high pass filter, active comparator, and noise reduction circuit that dynamically filters noise by generating trigger signals to activate the analog-to-digital converter only when photons are detected, reducing power consumption and preventing low and high frequency noise from reaching the converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high bandwidth amplifier is used to obtain spectral information in a photon counting system, then measurement precision is improved, but power consumption increases significantly
Solution Approach 1:
The patent extracts only the necessary spectral information from the X-ray photons using a photon counting approach, rather than amplifying the entire signal bandwidth. The charge sensitive amplifier integrates photon events over time, extracting spectral data only when photons are detected, thus avoiding continuous high-power amplification while maintaining measurement precision.
Solution Approach 2:
The system uses periodic gating of the amplifier, activating it only during photon detection events rather than continuous operation. The amplifier is triggered by photon arrival events, creating a periodic action pattern that reduces average power consumption while capturing all necessary spectral information during active periods.
2Measurement precision
If a high bandwidth amplifier is used to process spectral information, then measurement precision is improved, but noise increases
Solution Approach 1:
The patent extracts spectral information directly from individual photon counting events rather than from amplified continuous signals. By counting photons event-by-event and building spectra from these discrete measurements, the system avoids amplifying noise while preserving the spectral information contained in the photon energy distribution.
Solution Approach 2:
The patent converts the inherently noisy nature of photon detection into a benefit by using the discrete photon arrival events as triggering signals. Each photon event, which would be considered noise in continuous amplification systems, becomes a useful trigger that activates the amplifier only when needed, actually reducing overall noise while maintaining spectral precision.
3Measurement precision
If continuous signal processing is used to maintain low noise, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The system implements periodic action by gating the amplifier and signal processing chain to operate only during photon detection events. The amplifier is enabled briefly at each photon arrival to integrate the signal, then disabled during idle periods. This periodic operation maintains low noise during active processing while dramatically reducing average power consumption compared to continuous operation.
Solution Approach 2:
The photon detection events themselves serve as the trigger signals for amplifier activation, eliminating the need for external continuous clocking or control signals. The system is self-service in that the incoming photons automatically initiate the processing sequence, with each photon event generating its own processing window, thereby reducing overhead power consumption while maintaining signal integrity.
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 solution enhances signal gain, improves signal-to-noise ratio, and reduces power consumption by activating the ADC only during photon detection, thereby optimizing noise reduction and energy resolution without additional power requirements.
Implementation Method 1
A photodiode generates a current signal in response to received light
Implementation Method 2
A high pass filter is coupled to the CSA and receives the integrated signal and an inverse of an event signal, the high pass filter generates a coarse signal
Implementation Method 3
An active comparator is coupled to the high pass filter and receives the coarse signal and a primary reference voltage signal, the active comparator generates the event signal
Data Source
AI summary
In described examples, a charge sensitive amplifier (CSA) generates an integrated signal in response to a current signal. A high pass filter is coupled to the CSA and receives the integrated signal and an inverse of an event signal, the high pass filter generates a coarse signal. An active comparator is coupled to the high pass filter and receives the coarse signal and a primary reference voltage signal, the active comparator generates the event signal.