Photodiode Array Readout Controller with Canceling Process
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Solution Overview
Problem
Photodiode arrays using the storage readout method face challenges in maintaining a high signal-to-noise ratio while preventing saturation, especially when light intensity varies across different wavelengths, as the readout period must be optimized for each photodiode to avoid saturation and ensure accurate measurement.
Innovation Solution
A photodiode array with a readout controller that performs a canceling process before the complete readout operation, where signals from a predetermined number of photodiodes are read and then returned to the first photodiode, allowing for flexible setting of readout periods to prevent saturation and maintain high output levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the readout period is extended to improve signal-to-noise ratio for low-intensity light detection, then the S/N ratio is improved, but the photodiode junction capacitance becomes saturated
Solution Approach 1:
The patent applies preliminary action by performing a canceling readout process before the complete readout operation. This preliminary canceling process discharges accumulated charge from photodiodes that would otherwise saturate during the main integration period, enabling extended readout times for low-intensity signals without saturation while maintaining measurement accuracy.
2Reliability
If the readout period is shortened to prevent photodiode saturation, then saturation is avoided, but the signal-to-noise ratio decreases
Solution Approach 1:
The canceling readout process is performed preliminarily to remove excess charge before the main measurement integration. This allows the system to use longer integration periods for improved S/N ratio while the preliminary canceling step ensures that photodiodes do not saturate during the extended integration time.
3Measurement precision
If different readout periods are set for each photodiode to optimize detection, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the readout process into two distinct phases: a canceling readout phase and a complete readout phase. This segmentation allows different effective integration times for different photodiodes within a unified control framework, improving measurement accuracy without requiring complex individual control for each photodiode.
Solution Approach 2:
The patent implements periodic action through the alternating canceling and complete readout cycles. The canceling process periodically discharges accumulated charge from photodiodes, enabling the system to handle varying light intensities across different wavelengths through time-multiplexed operation rather than complex simultaneous control.
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 effectively maintains high signal-to-noise ratios and prevents photodiode saturation, enabling accurate measurements across a wide wavelength range without requiring significant improvements in processing capability or expensive, randomly accessible photodiode arrays.
Implementation Method 1
When illuminated with light, the photodiode 11 generates a photocurrent, which causes the electric charge to be discharged from the PD junction capacitor 12
Data Source
AI summary
An easy and inexpensive signal readout method is provided for a photodiode array consisting of n pieces of photodiodes whose signals are sequentially read out from the first through nth photodiodes. The method includes a canceling process that is performed one or more times before performing a complete readout operation for sequentially reading out signals from all the photodiodes, and the canceling process includes the steps of sequentially reading out signals of a predetermined number of photodiodes starting from the first photodiode to cancel the signals of these photodiodes and then returning to the readout of the signal of the first photodiode. According to this method, it is possible to easily set an appropriate charging time for each photodiode and yet prevent the photodiodes from becoming saturated.