Image Sensor Comparator With Switched Positive Feedback
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Solution Overview
Problem
Semiconductor image sensors face challenges in reducing power consumption and size due to the high number of comparators required for analog-to-digital conversion, which affects their performance and operational characteristics.
Innovation Solution
A comparator design incorporating a comparison circuit and a positive feedback circuit that generates an output signal more rapidly than the comparison signal, utilizing MOS transistors to connect and disconnect power supply voltages dynamically, thereby reducing static current and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional comparator design is used in image sensors, then analog-to-digital conversion can be performed, but power consumption increases due to static current in the positive feedback circuit
Solution Approach 1:
The patent applies periodic action by controlling the positive feedback circuit to operate only during specific phases of the conversion process. The switching circuit enables the positive feedback circuit periodically based on the state of the comparison circuit, allowing rapid transitions when needed while disabling static current flow during stable states, thus reducing overall power consumption without compromising conversion accuracy.
Solution Approach 2:
The patent implements dynamics by making the positive feedback circuit dynamically controllable through the switching circuit. The circuit transitions between active and inactive states based on real-time conditions, allowing the system to adapt its power consumption characteristics while maintaining the necessary functionality for accurate analog-to-digital conversion.
2Measurement precision
If the number of comparators is increased to achieve higher image sensor resolution, then measurement precision improves, but device complexity and occupation area increase
Solution Approach 1:
The patent applies universality by designing a comparator circuit that performs multiple functions within a single integrated structure. The positive feedback circuit, when activated, provides rapid transition capability that benefits all comparators in the array, while the shared switching control mechanism reduces individual comparator complexity. This multi-functional design allows high-resolution imaging without proportionally increasing overall system complexity.
3Speed
If a positive feedback circuit is added to accelerate output signal transitions, then speed improves, but power consumption increases due to static current
Solution Approach 1:
The patent resolves this contradiction by enabling the positive feedback circuit periodically rather than continuously. The switching circuit activates the positive feedback only during transition phases when rapid signal changes are needed, and disables it during stable states, thereby achieving fast transitions when required while minimizing static current consumption during operation.
Solution Approach 2:
The patent extracts the problematic static current component by introducing a switching circuit that selectively disconnects the positive feedback circuit from the power supply during non-critical periods. This separation allows the beneficial rapid transition capability to be retained when needed while removing the harmful continuous power consumption aspect.
Data Source
AI summary
A comparator includes a comparison circuit and a positive feedback circuit. The comparison circuit generates a comparison signal by comparing an input signal and a reference signal. The positive feedback circuit generates an output signal based on the comparison signal, such that the output signal transitions more rapidly than the comparison signal. The positive feedback circuit includes a first circuit configured to electrically connect a first power supply voltage to a conversion node in response to a transition of the comparison signal and electrically disconnect the first power supply voltage from the conversion node in response to a transition of the output signal, a second circuit configured to electrically connect a second power supply voltage to the conversion node in response to the transition of the output signal, and an output circuit configured to generate the output signal based on a voltage of the conversion node.