Threshold Uniformity Improvement in 1b Quanta Image Sensor Readout Circuit

Area of Science:

• * Solid-state device physics
• * Image sensor technology
• * Low-power electronics

Background:

• * Previous single-bit quanta image sensors (QIS) suffered from threshold non-uniformity in readout clusters.
• * This non-uniformity was attributed to common-mode voltage fluctuations at the quantizer input.
• * Addressing this limitation is crucial for advancing QIS performance.

Purpose of the Study:

• * To propose a new readout architecture for single-bit QIS.
• * To improve threshold uniformity and stability in QIS readout.
• * To reduce power consumption in high-speed QIS operation.

Main Methods:

• * Integration of a capacitive transimpedance amplifier (CTIA) before the 1-bit quantizer.
• * Implementation of a pipeline operation mode for simultaneous CTIA and ADC function.
• * Fabrication and testing of a 2048 × 1024 test chip using 45 nm/65 nm BSI CMOS image sensor process.

Main Results:

• * Demonstrated excellent threshold uniformity (0.3 to 0.8 e-) across readout clusters.
• * Achieved 500 frames per second (fps) equivalent timing.
• * Reported low power consumption of 68 mW.

Conclusions:

• * The proposed CTIA-based readout architecture effectively mitigates threshold non-uniformity in single-bit QIS.
• * The pipeline operation mode enhances power efficiency.
• * The results validate the architecture for high-speed, low-power image sensing applications.