Dynamic Gain Readout Circuit for Wide-Range Imaging
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Solution Overview
Problem
Existing imaging devices face challenges in achieving a large operating range with minimal capacitors, leading to increased manufacturing costs and decreased device density due to the need for multiple feedback capacitors in multi-channel image sensor devices.
Innovation Solution
A dynamic gain circuit that includes a variable capacitor and a charge dump circuit, where the charge dump circuit adjusts the input charge level based on detected voltage drops, allowing for auto-ranging with fewer capacitors and reducing the size of the feedback capacitors, thereby increasing device density and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple feedback capacitors are used to achieve a large operating range, then the operating range is improved, but the device density decreases and manufacturing costs increase
Solution Approach 1:
The patent combines multiple capacitor functions into a single feedback capacitor by using a dynamic gain circuit that adjusts its gain based on the input signal level. The charge dump circuit transfers charge between storage nodes to simulate the effect of multiple capacitors, allowing one physical capacitor to provide the equivalent functionality of multiple capacitors with different values.
Solution Approach 2:
The patent employs a dynamic gain circuit whose gain changes automatically based on the input signal level. The charge dump circuit dynamically adjusts the effective capacitance by transferring charge between different storage nodes, enabling the system to adapt to a wide operating range without requiring multiple fixed capacitors.
2Adaptability or versatility
If multiple feedback capacitors are used to achieve a large operating range, then the operating range is improved, but manufacturing costs increase
Solution Approach 1:
The patent merges multiple capacitor functions into a single feedback capacitor structure, reducing the number of discrete components that need to be manufactured and assembled. This consolidation directly reduces manufacturing complexity and cost while maintaining the ability to cover a large operating range through dynamic gain adjustment.
3Adaptability or versatility
If the size of feedback capacitors is increased to handle wide dynamic range, then the capacitance range is improved, but the lateral footprint increases
Solution Approach 1:
The patent uses a dynamic charge dumping mechanism that transfers charge between storage nodes based on the input signal level. This dynamic operation allows a small physical capacitor to effectively provide a large capacitance range by adjusting the charge storage and release timing, thereby maintaining wide dynamic range capability while minimizing the lateral footprint.
Solution Approach 2:
The patent changes the operational parameters of the feedback capacitor by dynamically adjusting the gain of the transimpedance amplifier and the timing of charge dump operations. This allows the same physical capacitor to effectively provide different capacitance values depending on the signal level, achieving a wide capacitance range without increasing the physical size.
Data Source
AI summary
A circuit includes an amplifier having an input and an output. A voltage comparator has an input and first and second outputs. The input of the voltage comparator is coupled to the output of the amplifier. A variable capacitor circuit is coupled between the input and the output of the amplifier and is coupled to the first output of the voltage comparator. A charge dump circuit has an input and an output. The input of the charge dump circuit is coupled to the second output of the voltage comparator. The output of the charge dump circuit is coupled to the input of the amplifier.