CMOS Image Sensor Readout Circuit Layout for Low-Noise High-Speed Transfer
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Solution Overview
Problem
CMOS image sensors face challenges in high-speed signal reading due to limited layout space, leading to increased wiring capacitance and resistance, and shared data transfer lines that cause noise and power consumption issues.
Innovation Solution
The solution involves a pixel-signal reading circuit with cascade-connected counters and latches organized on a column-by-column basis, using first and second switches to manage data transfer, and a timing control unit to coordinate data transfer signals, which reduces noise and power consumption while enabling high-speed operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixels are miniaturized and arranged densely to increase pixel count, then spatial resolution is improved, but wiring capacitance and resistance increase due to limited layout space
Solution Approach 1:
The patent transitions data transfer from vertical column-direction wiring to horizontal row-direction wiring by using shift registers that transfer data along rows. This dimensional change in data transfer direction reduces the impact of vertical wiring capacitance and resistance, allowing dense pixel arrangements while maintaining signal integrity.
Solution Approach 2:
The patent divides the data transfer function into multiple stages using shift registers segmented by row and column. Instead of direct vertical transfer from pixels to output, data is first transferred horizontally within rows through shift registers, then selectively read out. This segmentation reduces the capacitance and resistance burden on individual wiring paths.
2Device complexity
If shared data transfer lines are used to reduce wiring complexity, then device complexity is reduced, but noise and power consumption increase
Solution Approach 1:
The patent implements dynamic control of data transfer timing using clock signals and control circuits that activate specific shift registers at different times. By sequentially controlling which row's data is transferred and read out, the system reduces simultaneous switching noise and distributes power consumption over time, rather than having all columns transfer data simultaneously through shared lines.
Solution Approach 2:
The patent introduces shift registers as intermediary elements between the pixel array and output circuits. These shift registers buffer and condition signals, isolating the pixel array from direct connection to output lines. This intermediary structure reduces noise coupling and allows for controlled, sequential data extraction, lowering overall power consumption compared to direct shared-line connections.
3Speed
If high-speed analog signal processing is implemented, then reading speed is improved, but image quality degrades due to noise
Solution Approach 1:
The patent replaces high-speed analog signal processing with digital signal processing using shift registers and control circuits. Instead of relying on fast analog amplifiers and multiplexers that introduce noise, the system uses digital logic to transfer and select pixel data, achieving high reading speeds through parallel digital operations while maintaining signal integrity and reducing noise-related image quality degradation.
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 minimizes noise-induced errors, reduces power consumption, and enhances counter operation speed by separating counter and latch functions and optimizing data transfer within the limited layout space.
Implementation Method 1
a pixel section including a plurality of pixels arranged in a matrix, the plurality of pixels performing photoelectric conversion
Data Source
AI summary
A solid-state image pickup device and a camera system in which: (1) counters are organized into a counter group and a memory group on a column-by-column basis; (2) in each column, the individual counters are cascade-connected between individual bits; (3) switches are provided at bit output portions of the individual counters; (4) connecting sides of the individual switches are commonly connected to a column-signal transfer line, and output sides of the switches are shared with the other individual bits; (5) inputs of memories (latch circuits), which store digital data for horizontal transfer, share the column-signal transfer line; and (6) outputs of the memories corresponding to the individual bits are connected via switches to data transfer signal lines wired so as to be orthogonal to the column-signal transfer line.