A Multimodal CMOS Readout IC for SWIR Image Sensors with Dual-Mode BDI/DI Pixels and Column-Parallel Two-Step...

Area of Science:

• Electrical Engineering and Computer Science
• Optoelectronics and Imaging Technology

Background:

• Short-wave infrared (SWIR) image sensors require efficient analog front-end (AFE) circuits for optimal performance.
• Existing readout integrated circuits (ROICs) face trade-offs between injection efficiency, bias stability, and power consumption.
• Direct-injection (DI) offers low power but suffers from instability, while buffered-direct-injection (BDI) improves stability at higher power costs.

Purpose of the Study:

• To propose and implement a novel dual-mode CMOS analog front-end (AFE) circuit for SWIR image sensors.
• To dynamically balance injection efficiency and power consumption in the ROIC through a hybrid readout circuit.
• To enhance the signal-to-noise ratio (SNR) and linearity of the analog-to-digital converter (ADC).

Main Methods:

• Developed a hybrid readout circuit (ROIC) with dynamically switchable buffered-direct-injection (BDI) and direct-injection (DI) modes.
• Implemented a dual-mode injection architecture using in-pixel mode-switching transistors and a low-leakage transmission gate.
• Integrated a 12-bit two-step single-slope analog-to-digital converter (TS-SS ADC) with a four-terminal comparator and dynamic reference voltage compensation.

Main Results:

• The dual-mode ROIC successfully balances injection efficiency and power consumption based on pixel current levels.
• The TS-SS ADC achieved improved SNR and linearity by mitigating charge leakage and offset.
• The prototype AFE, fabricated in a 0.18 µm CMOS process, demonstrated a dynamic range of 75.58 dB, noise of 249.42 μV, and power consumption of 81.04 mW.

Conclusions:

• The proposed dual-mode AFE circuit effectively addresses the performance trade-offs in SWIR image sensor ROICs.
• The hybrid readout architecture enables adaptive operation, optimizing for low-noise or low-power conditions.
• This design provides a significant advancement for SWIR imaging systems requiring high performance and efficiency.