Switchable PGA-Comparator Circuit for Low-Power Image Sensor Readout
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Solution Overview
Problem
Existing image sensing array readout circuits face challenges in achieving low power consumption and small area occupancy while maintaining effective noise performance, as they require separate programmable gain amplifiers and comparators, leading to increased power usage and area requirements.
Innovation Solution
A combined programmable gain amplifier and comparator circuit is designed, where a single operational amplifier serves both functions, with switchable feedback capacitors and a diode clamp circuit, allowing for reconfiguration during different phases of operation to reduce noise and area consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate programmable gain amplifier and comparator are used, then noise performance and functionality are improved, but power consumption and area occupancy increase
Solution Approach 1:
The patent combines the programmable gain amplifier and comparator into a single integrated circuit block. The operational amplifier serves dual functions: during the integration phase it amplifies the pixel signal with programmable gain, and during the comparison phase it functions as a comparator to compare the amplified signal against a reference voltage. This merging eliminates the need for separate amplifier and comparator circuits, thereby reducing power consumption while maintaining noise performance through careful phase management and circuit design.
Solution Approach 2:
The operational amplifier is designed to perform multiple functions sequentially within the same circuit architecture. By using control switches to reconfigure the feedback network and input connections, the same amplifier circuit implements both the programmable gain amplification function and the comparator function at different time phases, maximizing resource utilization and minimizing overall power consumption.
2Adaptability or versatility
If separate programmable gain amplifier and comparator are used, then functionality is improved, but area occupancy increases
Solution Approach 1:
The patent integrates the programmable gain amplifier and comparator functionalities into a single shared operational amplifier circuit. The circuit uses time-division multiplexing where control switches reconfigure the amplifier's feedback path and input connections between the integration phase and comparison phase. This merging reduces the total silicon area required compared to implementing separate dedicated amplifier and comparator circuits.
Solution Approach 2:
The circuit employs dynamic reconfiguration through control switches that change the amplifier's operating mode based on the current phase. During integration, the amplifier operates in high-gain mode with appropriate feedback; during comparison, the same amplifier is reconfigured to operate as a comparator with different feedback connections. This dynamic switching allows one circuit to fulfill multiple functional roles, reducing area occupancy.
3Use of energy by stationary object
If integrated combined amplifier and comparator is used, then power consumption and area are reduced, but circuit complexity increases
Solution Approach 1:
The integrated circuit is divided into distinct functional phases (integration phase and comparison phase) with dedicated control logic for each. Control switches are segmented to perform specific reconfiguration tasks: some switches manage the feedback path, others manage input connections, and additional switches control the reset functionality. This segmentation of control functions simplifies the overall design by making each switch's purpose explicit and manageable.
Solution Approach 2:
The circuit performs preliminary actions by pre-charging or pre-discharging capacitors and pre-positioning switches to specific states before entering each operational phase. The reset switch is activated beforehand to clear any residual charges, and control signals are sequenced to ensure proper timing of switch transitions. This preliminary preparation reduces the complexity of managing transient states during phase transitions.
Data Source
AI summary
A switchable amplifier and comparator circuit includes an operational amplifier having an inverting input, a non-inverting input, a first differential output and a second differential output, the first differential output switchably coupled to the inverting input and the second differential output switchably coupled to the non-inverting input. A first feedback capacitor is coupled to the inverting input and switchably coupled to the first differential output, a second feedback capacitor is coupled to the non-inverting input and switchably coupled to the second differential output. A capacitive load is switchably coupled between the first differential output and the second differential output. A diode clamp circuit is switchably coupled between the first differential output and the second differential output. A resistive load is switchably coupled between the first differential output and the second differential output.