CMOS Pixel Circuit Capacitorless Readout for Low Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensor pixels with photodiodes exhibit high power consumption and noise issues due to capacitors and source followers, making them ineffective in low-light conditions where low power and low noise are required.
Innovation Solution
A pixel circuit with a first source follower, a photodiode, and a bias transistor, where a controllable switching element decouples capacitors from the output signal path, reducing noise and power consumption by excluding capacitors from the signal propagation and using the bias transistor as a switch to control the signal readout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitors and source followers are used in photodiode pixels, then signal amplification and storage are improved, but power consumption increases and noise is generated
Solution Approach 1:
The patent extracts and removes capacitors from the pixel circuit architecture, replacing them with a capacitorless readout mechanism using source followers and switching transistors. This eliminates kTC noise from capacitors while maintaining signal readout capability, directly reducing power consumption and noise in low-light conditions
2Measurement precision
If capacitors are used in photodiode pixels, then signal storage is improved, but kTC noise is generated
Solution Approach 1:
The patent removes capacitors from the signal path and replaces the storage function with a different mechanism using source followers and controlled switching. This extraction eliminates the kTC noise source while preserving the ability to store and readout photodiode signals through alternative circuit topology
3Measurement precision
If source followers are used in photodiode pixels, then signal amplification is improved, but RTS noise is generated
Solution Approach 1:
The patent applies local quality by using source followers selectively only when needed for signal readout, rather than continuously. The circuit employs controlled switching to activate source followers only during specific operation phases, reducing RTS noise generation while maintaining amplification capability when required
4Measurement precision
If capacitors are included in the signal path, then signal storage is improved, but power consumption and noise increase
Solution Approach 1:
The patent extracts capacitors from the signal path and replaces the storage function with voltage holding in source follower gates and controlled switching mechanisms. This eliminates the need for continuous capacitor charging/discharging operations, significantly reducing power consumption while maintaining signal storage capability
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 solution achieves low-noise signal readout, reduced power consumption, and increased dynamic range in low-light conditions, effectively addressing the limitations of existing CMOS image sensor pixels.
Implementation Method 1
Image sensors using photodiode pixels may be implemented in complementary metal oxide semiconductor (CMOS) architecture
Data Source
AI summary
An embodiment circuit includes a first source follower configured to be controlled by a voltage at a first node, a photodiode controllably coupled to the first node, and a bias transistor configured to be controlled by a bias voltage. The bias transistor has a first terminal coupled to an output of the first source follower. The circuit additionally includes a storage node controllably coupled to the output of the first source follower, and an amplifier controllably coupled between the storage node and an output line. Also included in the circuit is a controllable switching element configured to couple a second terminal of the bias transistor to a supply voltage in response to a pixel operating in a first mode, and to couple the second terminal of the bias transistor to the output line in response to the pixel operating in a second mode.