Solid-State Image Sensor Charge Sorting for Time-of-Flight Noise Rejection
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Solution Overview
Problem
Conventional solid-state image sensors face challenges in accurately measuring distance using the time-of-flight measurement method due to noise from unknown background light, which saturates the charge storage capacitors and invalidates the charge sorting action, making it difficult to achieve high sensitivity and low noise.
Innovation Solution
The implementation of a solid-state image sensor with a plurality of charge-storage sections and capacitors, where the capacitors have equal electric capacitance values, and connection switching circuits controlled by FET switches, allowing for the extraction of the difference component of charge stored in these sections, effectively eliminating noise from background light and isolating the signal component from the predetermined light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge storage capacitors are used to store photoelectrons generated by incoming light in conventional solid-state image sensors, then the basic time-of-flight measurement function is achieved, but noise from background light saturates the capacitors and invalidates the charge sorting action, making accurate measurement difficult
Solution Approach 1:
The patent divides the charge storage function into multiple separate capacitors (first capacitor, second capacitor, third capacitor, fourth capacitor) instead of using a single storage capacitor. Each capacitor stores charge from a specific photodiode, enabling independent processing and comparison of charge signals to eliminate background light noise through differential measurement.
Solution Approach 2:
The patent introduces transfer gates as intermediary elements between photodiodes and capacitors. These transfer gates control the timing and routing of charge flow, enabling synchronized charge transfer and facilitating the differential measurement process that rejects background light noise while preserving signal light information.
2Reliability
If conventional charge sorting methods are used with two or more charge storage capacitors connected to one photodiode, then signal-to-noise ratio is increased by reading out and averaging separated charge, but background light still causes saturation and the sorting action becomes invalid
Solution Approach 1:
The patent creates an asymmetric charge storage and processing architecture where different capacitors are associated with different photodiodes and processed differently through the readout circuitry. This asymmetric arrangement enables differential measurement that inherently rejects common-mode background light noise while preserving asymmetric signal light information.
Solution Approach 2:
The patent uses multiple capacitors with equal capacitance values that are sufficient to handle the expected charge range without saturation. By providing more storage capacity than minimally required and using differential comparison, the system can operate reliably even when individual capacitors might be subject to background light interference, as the differential measurement cancels out the common noise component.
3Adaptability or versatility
If high-frequency modulated light is used for time-of-flight measurement, then distance measurement capability is achieved, but the measurement becomes vulnerable to background light interference that appears as noise with insufficient signal-to-noise ratio
Solution Approach 1:
The patent employs periodic charge transfer operations synchronized with the high-frequency modulated light signal. Transfer gates are activated at specific periodic intervals to transfer charge from photodiodes to capacitors, enabling the system to track and measure the periodic modulation while rejecting non-synchronized background light through differential comparison of charge signals.
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 enables the effective extraction of the signal component from the reflection light, achieving high sensitivity and low noise in the time-of-flight measurement method, even in the presence of background light interference.
Implementation Method 1
photoelectrons generated by incoming light
Data Source
AI summary
A solid-state image sensor of a charge sorting method used in a time-of-flight measurement method, in which noise derived from background light, which is caused by the reflection light from the subject derived from background light is eliminated, reflection light from the subject derived from a predetermined light source, which is previously set in the solid-state image sensor, is effectively extracted as a signal component to achieve high sensitivity and low noise, which is a solid-state image sensor that is equipped with a plurality of charge-storage sections, discriminates photoelectrons generated by incoming light on the incoming timing and sort to the above-described plurality of charge-storage sections, and measures the timing of the incoming light, in which the sensor has: a plurality of capacitors that capable of conducting to the plurality of charge-storage sections; and a control section that controls a conducted state between the above-described plurality of charge-storage sections and the above-described plurality of capacitors, in which by selectively conducting the above-described plurality of charge-storage sections and the above-described plurality of capacitors by the control of the above-described control section, the difference component of charge stored in the above-described plurality of charge-storage sections is extracted.