CMOS Image Sensor Comparator Noise Reduction via Common Control Terminals
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors experience temporal flicker in image quality due to random noise in the differential input unit or active load of the comparator, which increases circuit area and noise power, making it difficult to reduce noise without increasing the circuit size.
Innovation Solution
A solid-state imaging element with a comparator that includes a differential input unit and an active load, where at least one transistor in the active load has multiple control terminals electrically connected in common, reducing transconductance and noise while maintaining a compact circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the area of the control terminal of the transistor is increased to reduce random noise, then the noise power is reduced, but the circuit area of the comparator increases
Solution Approach 1:
The transistor is divided into multiple identical transistors connected in parallel, where only a portion of the control terminals are connected to the signal input while others are left unconnected or connected to fixed potentials. This segmentation allows the effective control area to be reduced while maintaining sufficient noise performance through the combined effect of all transistor channels.
Solution Approach 2:
Different control terminals of the same transistor are given different connection states: some are connected to the signal input while others are left unconnected or connected to fixed potentials. This creates local quality differences within the transistor structure, allowing the effective control area to be selectively reduced without uniformly affecting the entire transistor, thereby reducing noise while controlling circuit area.
2Object-affected harmful factors
If multiple control terminals are electrically connected in common, then the transconductance is reduced and noise is reduced, but the circuit complexity increases
Solution Approach 1:
Multiple control terminals are electrically connected in common through wiring, merging them into a single functional unit. This combining approach reduces the effective transconductance and consequently reduces noise, while the wiring implementation keeps the added complexity minimal compared to alternative solutions.
Data Source
AI summary
A solid-state imaging element of the present disclosure includes: a pixel array in which a plurality of unit pixels is arranged in a matrix shape, the plurality of unit pixels each including a photoelectric conversion unit; and an analog-to-digital conversion unit that converts an analog pixel signal into a digital signal, the analog pixel signal being output from each of the plurality of unit pixels of the pixel array. Then, the analog-to-digital conversion unit includes a comparator that includes a differential input unit and an active load of the differential input unit, the differential input unit using, as an input, a prescribed reference signal and the analog pixel signal. At least one transistor that configures the active load includes a plurality of control terminals that controls current. The plurality of control terminals is electrically connected in common.