Archives for December 2025

Image Sensors World        Go to the original article...

In a recent paper titled "An Extended Time-Mode Digital Pixel CMOS Image Sensor for IoT Applications" Kim et al from Yonsei University write:

Time-mode digital pixel sensors have several advantages in Internet-of-Things applications, which require a compact circuit and low-power operation under poorly illuminated environments. Although the time-mode digitization technique can theoretically achieve a wide dynamic range by overcoming the supply voltage limitation, its practical dynamic range is limited by the maximum clock frequency and device leakage. This study proposes an extended time-mode digitization technique and a low-leakage pixel circuit to accommodate a wide range of light intensities with a small number of digital bits. The prototype sensor was fabricated in a 0.18 μm standard CMOS process, and the measurement results demonstrate its capability to accommodate a 0.03 lx minimum light intensity, providing a dynamic range figure-of-merit of 1.6 and a power figure-of-merit of 37 pJ/frame·pixel. 

 

Figure 1. Operation principle of conventional CISs: (a) voltage mode; (b) fixed reference; and (c) ramp-down TMD.Figure 2. Theoretical photo-transfer curve of conventional 6-bit TMDs.Figure 3. The operation principle of the proposed E-TMD technique.Figure 4. Theoretical photo-transfer curve of the proposed E-TMD: (a) TS = TU = TD = 2000tCK, Δ = 0; (b) TS = TU = TD = 100tCK, Δ = 0; (c) TS = TU = 0, TD = 45tCK, Δ = 0; and (d) TS = 0, TU = 25tCK, TD = 45tCK, Δ = 0.7.Figure 5. The conventional time-mode digital pixel CIS adapted from [11]: (a) architecture; (b) pixel schematic diagram.Figure 6. Architecture and schematic diagram of the proposed time-mode digital pixel CIS.Figure 7. Operation of the proposed time-mode digital pixel CIS with α representing VDD-vREF-VT: (a) six operation phases and (b) timing diagram.Figure 8. Transistor-level simulated photo-transfer curve comparison.

Figure 9. Chip micrograph.

 

Figure 10. Captured sample images: (a) 190 lx, TS = 17 ms, tCK = 50 µs; (b) 1.9 lx, TS = 400 ms, tCK = 2 µs.Figure 11. Captured sample images and their histograms: (a) 20.5 lx, TS = 32.6 ms; (b) 200.6 lux, TS = 4.6 ms; (c) 2106 lux, TS = 0.64 ms; (d) 2106 lux, TS = 0.64 ms, TU = 0.74 ms, TD = 1.84 ms, Δ = 0.5.

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