Solid-State Imaging Comparator Level Shifting for Wider Voltage Range
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Solution Overview
Problem
In solid-state imaging elements, the narrow voltage range caused by connecting a pMOS transistor, current source, and pixel circuit in series leads to potential malfunctions and leakage currents, limiting design flexibility and requiring increased power supply voltage and lowered thresholds.
Innovation Solution
Incorporating a level shift circuit that compares input potentials with reference potentials, outputs shifted potentials, and uses a logic gate and counter to determine threshold crossings, expanding the voltage range and preventing malfunctions and leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a pMOS transistor, current source, and pixel circuit are connected in series in a comparator, then power consumption is reduced by using a common power supply, but the voltage range on the input side of the inverter becomes narrow
Solution Approach 1:
A level shift circuit is introduced as an intermediary component between the comparison circuit and the inverter. This level shift circuit includes a pMOS transistor and nMOS transistor that work together to shift the voltage level of the comparison result signal, thereby expanding the voltage range available to the inverter input while maintaining the series connection configuration for power efficiency.
2Use of energy by stationary object
If the voltage range is narrow, then power consumption is reduced, but the inverter may malfunction or generate leakage current
Solution Approach 1:
The level shift circuit serves as a mediator that ensures the inverter receives signals within its reliable operating voltage range. By shifting the voltage levels appropriately, the level shift circuit prevents the inverter from operating in marginal conditions that would cause malfunction or leakage current, thus maintaining reliability while preserving the low power consumption benefits of the series connection.
3Reliability
If the power supply voltage is increased and threshold is lowered to prevent malfunction and leakage current, then reliability is improved, but the degree of freedom in design decreases
Solution Approach 1:
Instead of changing the power supply voltage or transistor thresholds to ensure reliable operation, the invention changes the voltage level parameters of the comparison result signal through the level shift circuit. This allows the inverter to operate reliably within its existing voltage range while maintaining design flexibility, as the level shift can be implemented without altering fundamental design parameters like supply voltage or device thresholds.
Data Source
AI summary
A degree of freedom in design is improved in a solid-state imaging element in which a logic gate is provided in a comparator. A comparison circuit compares an input potential which has been input with a predetermined reference potential and outputs any one of a pair of output potentials as a comparison result. A level shift circuit outputs any one of a pair of shift potentials having a larger potential difference than the pair of output potentials as an output signal on the basis of the comparison result. The logic gate determines whether or not the output signal is higher than a predetermined threshold between the pair of shift potentials and outputs a determination result. A counter counts a count value over a period until the determination result is inverted.