Light Sensor Split Differential Amplifier Routing Capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing light sensors, particularly ambient light sensors, face challenges due to the routing capacitance issue caused by long conductive wires connecting pixels to their readout circuits, which becomes problematic with island-type photodiodes that have significantly lower intrinsic capacitance.
Innovation Solution
The proposed solution involves a light sensor design where each pixel includes a split differential pair amplifier, with the first part common to all photodiodes and the second part associated with each photodiode. This configuration reduces the routing capacitance by placing the second part of the amplifier close to the photodiode, typically within 50 μm, and includes feedback loops and switches to manage signal coupling and disconnection effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the readout circuit is disposed at an end of a row or column associated with the pixel, then the routing is simplified, but the routing capacitance increases due to long conductive wires
Solution Approach 1:
The amplifier is divided into a first part (common to all photodiodes) and a second part (specific to each photodiode). The second part is disposed close to each photodiode while the first part is disposed at the row or column end, segmenting the readout circuit to balance routing simplicity and capacitance reduction.
Solution Approach 2:
The first part of the amplifier acts as an intermediary between the distributed second parts (close to photodiodes) and the external readout circuit. This intermediary structure allows local capacitance reduction while maintaining simplified external routing.
2Area of moving object
If island-type photodiodes are used to reduce pixel area, then the pixel size decreases, but the routing capacitance impact increases due to lower intrinsic capacitance
Solution Approach 1:
The patent applies different amplifier parts to different locations: the second part with low input capacitance is placed locally at each photodiode (especially island-type), while the first part handles common functions at the row/column end. This local optimization addresses the specific capacitance characteristics of island photodiodes.
3Reliability
If the amplifier is fully distributed close to each photodiode, then the routing capacitance is minimized, but the device complexity increases
Solution Approach 1:
The first part of the amplifier is merged and shared among multiple photodiodes, while only the essential second part is distributed to each photodiode. This merging approach reduces overall device complexity while maintaining the capacitance benefits of local amplification.
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 design effectively reduces the routing capacitance, improving the readout phase of pixels, especially those with island-type photodiodes, thereby enhancing the overall performance and accuracy of the light sensor.
Implementation Method 1
multiple pixels, each pixel including first photodiodes having each a terminal coupled to a first node of the pixel
Implementation Method 2
a first MOS transistor of a differential pair of the first amplifier, each second part of the first amplifier having a second MOS transistor of the differential pair
Data Source
AI summary
The present disclosure relates to a sensor having pixels, each pixel having photodiodes having each a terminal coupled to a first node associated with the photodiode; and an amplifier having a first part and, for each photodiode, a second part associated with the photodiode. The first part includes an output of the amplifier and a first MOS transistor of a differential pair. Each second part includes a second MOS transistor of the differential pair having its gate coupled to the first node associated with the photodiode the second part is associated with; a first switch coupling a source of the second transistor to the first part of the amplifier; and a second switch coupling a drain of the second transistor to the first part of the amplifier.