High-Sensitivity Radiation Sensing Circuit Design
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Solution Overview
Problem
Modern consumer electronics face challenges in achieving high-sensitivity radiation sensing due to limitations in photodiode leakage, dark current, and signal-to-noise ratio, especially in low-radiation environments, while also needing to consider cost, miniaturization, and power constraints.
Innovation Solution
A circuit design that includes a transistor for resetting voltage levels, measurement circuitry for voltage measurement at the start and end of an integration period, an island photodiode for minimized leakage, a capacitor for accurate charge measurement, and an error amplifier to minimize bias, allowing for high-sensitivity radiation detection by accounting for systematic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiodes are used for radiation detection, then radiation sensing capability is provided, but leakage and dark current affect measurement accuracy
Solution Approach 1:
The patent extracts and separates the harmful dark current component from the total measured current. By performing measurements at two different times (with and without radiation exposure) and calculating the difference, the circuit isolates the radiation-induced photocurrent from the photodiode's inherent leakage and dark current, thereby eliminating their effect on measurement accuracy.
2Measurement precision
If highly accurate measurement circuitry is implemented, then measurement precision improves, but crosstalk and parasitic capacitance introduce errors
Solution Approach 1:
The patent employs a feedback mechanism where the measured voltage level is used to control the switching of the photodiode connection to the measurement circuitry. The processing circuitry uses the measured values to determine when to connect or disconnect the photodiode, creating a feedback loop that optimizes the measurement process and minimizes the impact of parasitic effects.
Solution Approach 2:
The patent performs a preliminary measurement of the voltage level before radiation exposure (or with the photodiode disconnected) to establish a baseline value. This preliminary action allows the system to later subtract this baseline from the radiation-exposure measurement, thereby compensating for parasitic capacitance and crosstalk effects that are present in both measurements.
3Measurement precision
If sensors are designed for high sensitivity and accuracy, then radiation detection capability improves, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated circuit structure. The measurement circuitry serves dual purposes: it measures both the baseline voltage level (without radiation) and the voltage level during radiation exposure. By merging these measurement functions and using differential calculation, the circuit achieves high accuracy without requiring separate complex measurement systems for each function.
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
The circuit achieves extremely high-sensitivity measurements of incident radiation intensity by accounting for errors like dark current and minimizing leakage, while maintaining a high signal-to-noise ratio, suitable for applications like ambient light sensing and flicker detection.
Implementation Method 1
at least one photodiode configured to vary the voltage-level at the circuit node in response to radiation incident upon the photodiode
Data Source
AI summary
A circuit for sensing radiation with high sensitivity is disclosed. The circuit comprises a first transistor configurable to reset a voltage-level at a circuit node to a voltage reference. The circuit also comprises measurement circuitry configured to measure the voltage-level at the circuit node, and at least one photodiode configured to vary the voltage-level at the circuit node in response to radiation incident upon the photodiode during an integration period. The circuit also comprises processing circuitry configured to control the first transistor to reset the voltage-level at the circuit node and to subsequently configure the measurement circuitry to measure the voltage-level at a start and at an end of the integration period.