BioFET Cascade Readout Circuit Using Time-Domain Digital Sensing
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Solution Overview
Problem
Biosensors that incorporate transistors face challenges with analog signal processing, as these signals are prone to noise and require additional circuitry, increasing power consumption and chip costs, and the integration of analog-to-digital converters further complicates the system.
Innovation Solution
The use of dual-gate back-side sensing FET sensors with digital readout circuits that incorporate bioFET sensors, which enable label-free detection and reduce power consumption by utilizing digital components to measure sensing signals, thereby minimizing noise and chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog signal processing is used to read out biosensor signals, then the detection capability is maintained, but power consumption increases and the system becomes more complex
Solution Approach 1:
The patent replaces analog signal processing circuits with a digital readout circuit that uses a charge-to-digital converter. The bioFET sensor output, which is typically an analog signal, is directly converted to a digital signal through a charge amplifier and flash ADC, eliminating the need for complex analog filtering, amplification, and modulation circuits. This substitution of digital for analog processing significantly reduces power consumption while maintaining detection capability.
Solution Approach 2:
The patent changes the signal domain from analog to digital by introducing a flash ADC that converts the charge signal from the bioFET directly into a digital value. This parameter change in signal representation allows the system to maintain full detection capability while operating in a digital domain that consumes less power and is more resistant to noise.
2Difficulty of detecting and measuring
If additional circuitry is added to process analog signals, then signal processing capability is improved, but chip area increases and manufacturing cost increases
Solution Approach 1:
The patent merges the signal processing function directly into the sensor readout circuit by integrating a charge amplifier and flash ADC in close proximity to the bioFET sensor elements. This integration allows multiple functions (charge amplification, analog-to-digital conversion, and digital signal processing) to be combined in a single compact circuit block, reducing the total chip area required compared to separate analog processing stages.
Solution Approach 2:
The patent replaces extensive analog signal processing circuitry with a streamlined digital readout system. The flash ADC and subsequent digital logic circuits occupy less area than equivalent analog filtering, amplification, and modulation circuits would require, while providing equal or superior signal processing capability.
3Object-affected harmful factors
If analog-to-digital converter is integrated to produce digital signal, then noise resistance is improved, but device complexity and chip cost increase
Solution Approach 1:
The patent applies preliminary action by performing charge amplification immediately at the sensor output before the analog signal can be corrupted by noise. The charge amplifier converts the tiny charge signal from the bioFET into a larger voltage signal that is then quickly converted to digital form. This preliminary amplification and conversion before noise contamination reduces the need for complex noise filtering circuits.
Solution Approach 2:
The patent replaces complex analog noise filtering and signal conditioning circuits with a direct flash ADC conversion approach. The digital domain inherently provides noise immunity, eliminating the need for sophisticated analog noise rejection techniques 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 approach allows for efficient, low-power detection of biomolecules with reduced chip area and cost, enabling precise quantification of analytes without the need for costly labeling processes.
Implementation Method 1
Biosensors that include transistors are sensors that electrically sense charges, photons, and mechanical properties of bio-entities or biomolecules
Data Source
AI summary
Various bioFET sensor readout circuits and their methods of operation are described. A readout circuit includes a plurality of logic gates coupled in cascade, a delay extractor, and a counting module. Each logic gate of the plurality of logic gates includes at least one bioFET sensor. The delay extractor is designed to generate a pulse-width signal based on a time difference between an output signal from the plurality of logic gates and a reference signal. The counting module is designed to receive the pulse-width signal and output a digital count corresponding to a width of the pulse-width signal.