CMOS Sensor Readout Amplifier With Multi-Phase Noise Filtering
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Solution Overview
Problem
CMOS imaging sensors face challenges in reducing readout noise due to large capacitors required in readout circuitry, which increase the area and cost of the imaging array, and require significant charging time and power for buffer amplifiers.
Innovation Solution
A low-noise amplifier and imaging array design that uses a smaller filter capacitor and introduces a third phase in the readout process, along with a unit gain or higher gain buffer amplifier, to reduce noise and minimize the size and power requirements, allowing for a more compact and efficient imaging array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large capacitors are used in the readout circuitry to reduce readout noise, then noise performance is improved, but the area of the imaging array increases significantly
Solution Approach 1:
The patent divides the readout process into multiple phases (first time period with buffer amplifier connected, second time period with buffer amplifier disconnected) and uses multiple capacitors (first filter capacitor, second filter capacitor) with different functions. This segmentation allows each component to be optimized for its specific role, enabling noise reduction without requiring a single large capacitor that would consume excessive area.
Solution Approach 2:
The patent transitions from a single-capacitor approach to a multi-capacitor system operating in different time dimensions. By using capacitors with different capacitance values in different phases of the readout process, the system achieves equivalent noise filtering performance with smaller individual capacitor sizes, thereby reducing total area.
2Measurement precision
If large capacitors are used in the readout circuitry to reduce readout noise, then noise performance is improved, but the cost increases
Solution Approach 1:
The patent segments the filtering function across multiple capacitors with different capacitance values rather than using one large capacitor. This segmentation allows the use of smaller, more cost-effective capacitor components while achieving the same overall noise reduction performance, thereby reducing manufacturing cost.
3Measurement precision
If buffer amplifier is used to charge the filter capacitor, then noise filtering is improved, but charging time and power consumption increase
Solution Approach 1:
The patent segments the charging process into two distinct phases: a first time period where the buffer amplifier is connected to charge the first filter capacitor, and a second time period where the buffer amplifier is disconnected and a second filter capacitor is used. This segmentation allows the buffer amplifier to charge only the smaller first capacitor quickly, reducing charging time and power consumption while maintaining noise filtering performance through the second capacitor.
Solution Approach 2:
The patent dynamically switches between different circuit configurations depending on the operational phase. During the first time period, the buffer amplifier is connected for rapid charging; during the second time period, it is disconnected for low-power noise filtering. This dynamic operation optimizes both charging speed and power efficiency.
Data Source
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AI summary
A low-noise amplifier is disclosed. The amplifier includes a signal amplifier having an amplifier signal output, a first filter capacitor, a buffer amplifier having a buffer amplifier input and a buffer amplifier output; and a switching network. The first filter capacitor has first and second terminals. The second terminal is connected to a power rail. The amplifier signal output is connected to the buffer amplifier input by a first direct current path and the buffer amplifier output to the first terminal of the first filter capacitor by a second direct current path during a first time period. The amplifier signal output is connected directly to the first terminal of the first filter capacitor by a third direct current path during a second time period, and the amplifier signal output to the first terminal of the first filter capacitor through a resistor during a third time period.