CMOS Image Sensor Noise Cancellation via Dummy Pixel Subtraction
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Solution Overview
Problem
CMOS image sensors face challenges in reducing power noise, especially at low light conditions, as existing methods like on-chip and off-chip RC filters and regulators fail to effectively filter out high-frequency noise, impacting sensing quality.
Innovation Solution
A sensing device with a pixel array and readout circuit that uses a subtraction operation between a sensing signal and a reference signal to generate readout data, where the reference signal is derived from a pixel group not detecting light, effectively canceling out power noise components from the sensing signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an on-chip RC filter is used to filter power noise, then the filtering function is integrated into the chip, but high-frequency noise is not easily filtered out
Solution Approach 1:
The patent introduces a dummy pixel group as an intermediary element that generates a reference signal representing power noise. This reference signal is then subtracted from the sensing signal to eliminate noise, effectively using the dummy pixel as a mediator to extract and remove noise components without requiring traditional filtering circuits.
Solution Approach 2:
The patent extracts the power noise component from the sensing signal by using the dummy pixel group to generate a separate reference signal that contains only the noise. This extracted noise is then subtracted from the original sensing signal, separating the useful light detection signal from the harmful power noise.
2Measurement precision
If an off-chip RC filter is used to filter power noise, then high-frequency noise filtering is improved, but the cost of the CMOS image sensor increases
Solution Approach 1:
The patent implements a self-service solution where the dummy pixel group within the sensor array itself generates the reference signal needed for noise cancellation. This eliminates the need for external off-chip filtering components, reducing manufacturing cost while maintaining effective noise filtering through the subtraction operation in the readout circuit.
3Stability of the object's composition
If a regulator is used to generate clear power with low noise, then power stability is improved, but high-frequency noise is not easily filtered out
Solution Approach 1:
The patent performs preliminary action by having the dummy pixel group continuously track and generate a reference signal that represents the power noise characteristics. This reference signal is prepared in advance and simultaneously available when needed for subtraction, allowing proactive noise cancellation rather than reactive filtering.
Data Source
AI summary
A sensing device is provided. The sensing device includes a plurality of pixel groups and a readout circuit. The pixel groups are arranged on a plurality of rows and a plurality of columns to form a pixel array. The pixel groups include a first pixel group and a second pixel group which are arranged on the different rows and the same column. The readout circuit is coupled to the pixel groups. When the first pixel group is triggered to perform a readout operation to generate a first sensing signal, the second pixel group performs a coupling operation to generate a reference signal. The readout circuit performs a subtraction operation based on the first sensing signal and the reference signal to generate a first readout data corresponding to the readout operation of the first pixel group.