Light Sensor Split Amplifier Routing Capacitance
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Solution Overview
Problem
Known light sensors with island-type photodiodes face issues due to low intrinsic capacitance, leading to significant routing capacitance challenges during the readout phase, which affects their performance.
Innovation Solution
The design incorporates a split differential pair amplifier structure where each photodiode has a second part of the amplifier disposed close to it, reducing routing capacitance by selectively coupling each second part to a common first part using switches, and includes feedback loops with capacitive elements to manage capacitance 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 on the input of the readout circuit increases
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 end of the row or column, segmenting the readout circuit to reduce routing capacitance impact on signal processing speed.
2Area of moving object
If island-type photodiodes are used, then the pixel area is reduced, but the routing capacitance becomes dominant due to low intrinsic capacitance
Solution Approach 1:
The amplifier is segmented into two parts: the second part with the differential pair is disposed close to each island photodiode to minimize routing capacitance, while the first part with the integration capacitor is disposed at the row/column end. This segmentation allows compact pixel design while maintaining signal integrity.
Solution Approach 2:
The second part of the amplifier acts as an intermediary between the photodiode and the first part, providing local signal conditioning that compensates for the low intrinsic capacitance of island photodiodes and reduces the impact of routing capacitance.
3Speed
If the second part of the amplifier is disposed close to each photodiode, then the routing capacitance is reduced, but the device complexity increases
Solution Approach 1:
The amplifier is segmented into modular first and second parts that can be independently designed and optimized. The second part is replicated near each photodiode while the first part is shared, reducing overall complexity compared to having complete amplifiers at each pixel location.
Solution Approach 2:
The first part of the amplifier serves as a common resource for all photodiodes in the row or column, performing integration and output functions universally, while the second part handles photodiode-specific signal conditioning, reducing redundant circuitry.
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 configuration reduces routing capacitance and improves the readout efficiency of light sensors, particularly those with island photodiodes, by minimizing the impact of capacitance on signal processing.
Implementation Method 1
a first photodiode PD1 having a first electrode, or terminal, coupled to a first node IN1-21 of the pixel 1
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.