Solid-State Imaging Device Charge Pump Noise Reduction
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Solution Overview
Problem
Conventional solid-state imaging devices experience random horizontal line noise due to asynchronous operation of charge pump circuits with pixel reading times, leading to fluctuations in output potential, which degrade image quality, especially in smaller pixel cells and back-side illuminated devices.
Innovation Solution
Incorporating a control circuit that stops the driving clock signal during pixel reading times, synchronizing the charge pump circuit operations with pixel reading, thereby stabilizing the output potential and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the charge pump circuit operates asynchronously with pixel reading times, then the output potential fluctuates, but the device complexity remains low
Solution Approach 1:
The patent implements a feedback mechanism where the operation of the charge pump circuit is controlled based on the reading status of pixel signals. The control circuit monitors whether pixel signals are being read and adjusts the charge pump operation accordingly, creating a closed-loop system that stabilizes output potential by preventing fluctuations during critical reading periods
Solution Approach 2:
The patent applies preliminary action by controlling the charge pump circuit to stop operating before pixel signal reading begins. The control circuit anticipates the reading period and pre-adjusts the charge pump status to avoid potential fluctuations during the actual reading process, thereby preventing noise generation
2Object-affected harmful factors
If the charge pump circuit is stopped during pixel reading, then noise is reduced, but the productivity of signal processing decreases
Solution Approach 1:
The patent implements periodic action by alternating the operation state of the charge pump circuit based on the reading schedule. The charge pump operates periodically during non-reading periods to maintain potential levels, then stops during reading periods to eliminate noise, creating a rhythmic operation pattern that balances noise reduction with functional requirements
Solution Approach 2:
The patent applies dynamics by making the charge pump circuit's operation state variable rather than fixed. The control circuit dynamically adjusts the charge pump's on/off status based on real-time reading conditions, allowing the system to adapt its behavior to optimize both noise performance and processing efficiency under different operating conditions
Data Source
AI summary
A solid-state imaging device according to the present invention includes a pixel cell having a photodiode, a charge detection unit, an amplification transistor, a transfer transistor which transfers a signal charge to the charge detection unit in accordance with a transfer control signal, and a reset transistor which resets the charge detection unit in accordance with a reset control signal; a signal processing circuit which receives a pixel reset potential of the charge detection unit, and a pixel signal potential corresponding to the signal charge transferred to the charge detection unit; a charge pump circuit which steps up or steps down a potential of at least one of the transfer control signal and the reset control signal in accordance with a driving clock signal; and a control logic circuit which causes the driving clock signal to be stopped during a pixel reading time period.