CMOS Pixel Circuit Dynamic Mode Switching for Wide Dynamic Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors have a limited dynamic range due to the initial charge stored in the photodiode, making it difficult to detect both strong and weak light effectively, and existing methods to widen the dynamic range either increase power consumption or require larger circuits.
Innovation Solution
A photo detection device with pixel circuits that switch between two modes based on light intensity, using a first sensing circuit for small light amounts and a second sensing circuit for large light amounts, with controlled gain and storage time, allowing for a wider dynamic range without increasing power consumption or circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photodiode is charged with a fixed supply voltage and the storage time is extended to detect weak light, then the sensitivity for weak light is improved, but the dynamic range is limited because strong light causes complete charge discharge within the storage time
Solution Approach 1:
The patent applies dynamics by making the storage time variable rather than fixed. The control circuit dynamically adjusts the storage time based on the intensity of incident light: extending storage time for weak light to improve detection sensitivity, and shortening it for strong light to prevent complete charge discharge and maintain dynamic range. This resolves the contradiction between sensitivity and dynamic range adaptability.
2Adaptability or versatility
If logarithmic conversion or gain changing is used to widen the dynamic range, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The patent changes the parameter of storage time dynamically based on light intensity conditions. By controlling the storage time parameter rather than using complex logarithmic conversion circuits or multiple gain stages, the system achieves extended dynamic range with minimal additional circuitry. The control circuit simply adjusts the duration for which the photodiode stores charge, avoiding the complexity of analog-to-digital conversion, logarithmic amplifiers, or multi-gain transistor networks.
3Adaptability or versatility
If the storage time is shortened to detect strong light, then the dynamic range is improved, but the sensitivity for weak light detection deteriorates
Solution Approach 1:
The system dynamically adapts the storage time parameter according to the intensity of incident light. When strong light is detected, the storage time is shortened to prevent complete charge discharge and maintain the ability to detect variations in light intensity. When weak light is detected, the storage time is extended to accumulate sufficient charge for sensitive detection. This dynamic parameter adjustment resolves the contradiction between dynamic range and detection sensitivity.
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 device effectively widens the dynamic range by switching between modes based on light intensity, enabling detection of both small and large light amounts without the limitations of conventional technologies, reducing power consumption and circuit complexity.
Implementation Method 1
Each pixel of a CMOS sensor has a structure including a photodiode and a switch using MOSFETs... if light strikes the photodiode PD, a photocurrent will flow, and electric charge stored at the cathode terminal of the photodiode PD will be discharged
Data Source
AI summary
A pixel includes a photodiode, an overflow circuit, a first sensing circuit, and a second sensing circuit. The first sensing circuit charges and discharges a cathode capacitance by a photocurrent flowing through a photodiode, and amplifies an obtained voltage by a source follower amplifier so as to be outputted to a data line. The second sensing circuit charges and discharged the cathode capacitance by the photocurrent flowing through the photodiode, and outputs electric charge stored in the cathode capacitance via the data line. A pixel circuit is configured so that a first mode in which the first sensing circuit becomes active and a second mode in which the second sensing circuit becomes active can be switched. The first mode and the second mode are switched according to an amount of light received by the photodiode included in each pixel circuit. Gain is controlled according to the amount of light received, in the first mode, and the storage time is controlled in the second mode.