CT Integrator Circuit Dynamic Feedback Capacitance Noise Reduction

Solution Overview

Problem

Existing CT detector circuits face challenges in achieving improved noise performance across a high dynamic range without compromising performance at either smaller or larger signal magnitudes, as integrators designed for one range often fall short at the other.

Innovation Solution

The integrator circuit selectively connects and disconnects feedback capacitors and uses a shunt capacitor to optimize noise performance, reducing feedback capacitance at lower signal levels and increasing it at higher levels, while the shunt capacitance is sized to reduce noise bandwidth at smaller signal levels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If feedback capacitance is reduced to improve noise performance at smaller signal levels, then noise performance is improved, but full scale performance for larger signals deteriorates

Engineering Contradiction:

Improvenoise performanceVSAvoidfull scale performance

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The integrator circuit dynamically switches between different feedback capacitance values based on the signal level. A first feedback capacitor is used for smaller signal levels to optimize noise performance, while a second feedback capacitor with different capacitance is switched in for larger signal levels to maintain full scale performance. This dynamic adaptation resolves the contradiction by making the feedback capacitance variable rather than fixed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit changes the feedback capacitance parameter according to the signal amplitude. The control circuit monitors the signal level and selectively connects different feedback capacitors to the integrator, thereby adjusting the feedback capacitance parameter to match the current operating conditions. This parameter change enables optimal noise performance at low signals while preserving full scale capability at high signals.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If feedback capacitance is increased to improve full scale performance for larger signals, then full scale performance is improved, but noise performance at smaller signal levels deteriorates

Engineering Contradiction:

Improvefull scale performanceVSAvoidnoise performance

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The integrator circuit dynamically switches between different feedback capacitance values based on the signal level. A first feedback capacitor is used for smaller signal levels to optimize noise performance, while a second feedback capacitor with different capacitance is switched in for larger signal levels to maintain full scale performance. This dynamic adaptation resolves the contradiction by making the feedback capacitance variable rather than fixed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit changes the feedback capacitance parameter according to the signal amplitude. The control circuit monitors the signal level and selectively connects different feedback capacitors to the integrator, thereby adjusting the feedback capacitance parameter to match the current operating conditions. This parameter change enables optimal noise performance at low signals while preserving full scale capability at high signals.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If shunt capacitance is reduced to reduce noise bandwidth at smaller signal levels, then noise performance is improved, but signal handling capability for larger signals deteriorates

Engineering Contradiction:

Improvenoise performanceVSAvoidsignal handling capability

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The shunt capacitance is dynamically adjusted based on signal level through selective switching of capacitor arrays. At smaller signal levels, the shunt capacitance is reduced to minimize noise bandwidth and improve noise performance. At larger signal levels, the shunt capacitance is increased to maintain proper signal handling capability and prevent saturation. This dynamic adjustment resolves the contradiction between noise performance and signal handling capability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit changes the shunt capacitance parameter according to the signal amplitude. The control circuit adjusts the shunt capacitance value to match the current signal level, thereby optimizing the noise bandwidth for small signals while maintaining adequate signal handling capability for large signals. This parameter adaptation enables the circuit to achieve both low noise performance and robust signal handling.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8824626B2Reduced-noise integrator, detector and CT circuits

Publication Date: 2014.09.02 ANALOG DEVICES INC

AI summary

A detector circuit can include an integrator having an amplifier, a first feedback capacitor connected between an input and output of the amplifier, one or more additional feedback capacitors connected by at least one switch between the input and output of the amplifier, and a shunt capacitor connected to the output of the amplifier. The shunt capacitor can be selected to have a capacitance value greater than that of a minimum but less than that of a maximum feedback capacitance. The detector circuit can further include a sampling circuit having a sampling capacitor connected to the output of the integrator amplifier through at least one switch, wherein the sampling capacitor is separate from the shunt capacitor. A computed tomography imaging apparatus can include the detector circuit.