GC Detector Digital Subtraction for Low-Noise TCD Measurement
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Solution Overview
Problem
Current Gas Chromatograph (GC) measurement systems face challenges with Sigma-Delta A/D converters, which are not optimally suited for GC applications due to their focus on consumer devices, leading to issues with power reduction, signal voltage compatibility, and noise optimization in the sub-hertz region, resulting in suboptimal Signal-to-Noise Ratio (SNR) and high costs.
Innovation Solution
The implementation of a digital logic-based Sigma-Delta A/D converter system that eliminates the integrator and achieves the Σ factor in a digital form, using a Field Programmable Gate Array (FPGA) or similar digital logic to provide a highly resolved difference signal directly to the detector channels, reducing the need for analog components and improving SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If monolithic Sigma-Delta A/D converters are used with focus on low power consumer devices, then power consumption is reduced, but signal voltage compatibility and SNR performance deteriorate for GC applications
Solution Approach 1:
The patent changes the operating voltage parameter from low voltage (consumer device standard) to higher voltage (5V or more) to achieve the required signal levels for TCD detectors. This parameter change enables compatibility with GC detector output signals while maintaining low power consumption through efficient digital logic design.
Solution Approach 2:
The patent replaces the traditional analog integrator and analog difference amplifier with digital logic circuits implemented in FPGA or ASIC. This substitution eliminates the need for high-precision analog components and enables optimized power consumption while maintaining or improving SNR performance through digital signal processing.
2Adaptability or versatility
If the signal voltage is reduced in gain before A/D conversion to match lower voltage A/D, then voltage compatibility is improved, but SNR deteriorates
Solution Approach 1:
Instead of reducing the signal voltage to match low-voltage A/D converters, the patent inverts the approach by using high-voltage A/D converters (5V or more) that can directly accommodate the full dynamic range of TCD detector outputs. This eliminates the need for signal attenuation and preserves the SNR.
3Measurement precision
If an integrator is included in the Sigma-Delta A/D converter, then conversion accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and removes the analog integrator component from the Sigma-Delta A/D conversion architecture. The integration function is replaced by digital accumulation logic implemented in FPGA or ASIC, which achieves the same mathematical function with reduced component count and lower cost while maintaining conversion accuracy.
Solution Approach 2:
The patent uses digital logic to replicate the mathematical function of the analog integrator. The digital accumulation circuit performs the same integration operation on the quantized signal, producing equivalent results without requiring precision analog capacitors and resistors.
4Measurement precision
If analog difference amplifier is used to remove common mode range, then signal resolution is improved, but noise and drift increase
Solution Approach 1:
The patent replaces the analog difference amplifier with a digital subtraction circuit. The common mode rejection function is performed in the digital domain after A/D conversion, eliminating the introduction of analog noise and drift that occurs in the difference amplifier stage. The digital logic performs the subtraction without adding thermal noise or offset drift.
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 approach enhances the SNR and reduces noise and drift, achieving a more efficient and cost-effective A/D conversion for GC systems by eliminating the internal sigma block and analog difference amplifier, allowing for higher voltage operation and improved dynamic range without compromising noise and drift performance.
Implementation Method 1
A Thermal Conductivity Detector (TCD) requires a certain amount of power to operate properly in a GC application. The thermal conductivity of the common GC carrier gasses Hydrogen and Helium is fixed.
Data Source
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AI summary
A Gas Chromatograph (GC) detector comprises a first amplifier circuit (302(1)), a second amplifier circuit (302(2)), a digital subtractor (320) and a digital logic (325) to provide a GC measurement signal (330) in a digital form. Said first circuit (302(1)) includes a reference amplifier (332) comprising a first resistive bridge (337(1)), a first counter circuitry (305(1)) to provide a first counter output (317(1))). Said second circuit (302(2)) includes an amplifier (342) comprising a second resistive bridge (317(2)), a second counter circuitry (305(2)) to provide a second counter output (317(2)). Said digital subtractor (320) subtracts the first counter output (317(1)) from the second counter output (317(2)) and provides a digital subtractor output (322). Said digital logic (325) shared between one to many detector channels to implement at least a portion of the first counter circuitry and the second counter circuitry is arranged to receive the digital subtractor output (322) and provides the GC measurement signal (330). The GC detector (300) may be based on a Thermal Conductivity Detectors (TCD) (335(1),(335(2)) in which an analog difference amplifier and an integrator of a Sigma-Delta (Σ-Δ) A/D converter are eliminated and the Σ factor of the Sigma-Delta (Σ-Δ) A/D converter is accomplished in a digital form.