An image sensor converts optical signals into electrical signals, which are subsequently processed by an image signal processor (ISP) to generate still photos or video footage. CMOS image sensors feature two shutter mechanisms: rolling shutter and global shutter.

The illustration mentioned below intuitively demonstrates the differences between the two shutter modes when capturing fast-moving objects. For rolling shutter, the difference in exposure timing among pixel rows results in the rolling shutter distortion (jello effect).

Rolling Shutter: Pixels are not exposed simultaneously; exposure proceeds row by row. This creates time offsets in the start of exposure for each row within a single frame.

Global Shutter: All pixels begin and end exposure at the identical moment, followed by sequential pixel readout. Since every pixel shares the exact same exposure window with no time lag, jello effect is eliminated when shooting fast-moving subjects.

Unlike rolling shutter sensors, global shutter sensors are evaluated by a critical parameter known as Parasitic Light Sensitivity (PLS). It describes the sensor’s sensitivity to incident light after the shutter closes. PLS is measured in decibels (dB), and a lower value indicates better performance.

Implementing global shutter requires more complex circuitry compared to rolling shutter. There are three mainstream approaches to realize global shutter architecture:

Charge Domain

After photons are converted into electrons, the charges are stored in memory nodes prior to conversion into voltage signals.Advantage: Supports Correlated Double Sampling (CDS) and delivers favorable noise performance.Disadvantage: Storage cells occupy part of the light-sensitive area, reducing sensor sensitivity.

Voltage Domain

Photons are converted into electrons, transferred to floating diffusion (FD) nodes to form voltage signals, and then stored in memory nodes. This architecture generally suffers from inferior noise characteristics.

Digital Domain

This concept has emerged in recent years alongside advancements in semiconductor manufacturing. To implement digital-domain global shutter, signals must be output in real time, meaning each pixel requires an independent analog-to-digital converter (ADC). This technology remains confined to academic research and is not yet commercially available.

Turning to Sony’s global shutter sensors: Sony launched its first-generation Pregius CMOS sensor, the 2.3 MP IMX174 with a 5.78 μm pixel size, back in 2013. Compared with earlier generations, the 4th-generation Pregius S incorporates the following upgrades:

1. Pregius S marks Sony’s first adoption of Backside Illumination (BSI) technology in global shutter sensors. It enables smaller pixel dimensions while preserving outstanding image quality, with pixel size reduced to 2.76 μm.
2. Higher resolution and boosted frame rates Resolution is upgraded up to 24.5 MP, and frame rates are substantially improved versus previous generations.
3. Wider incident angle and enhanced sensitivity
4. Expanded functional capabilities Pregius S supports Dual ADC, enabling high-gain and low-gain analog readout within one frame, with signal combination processed on-sensor to achieve HDR imaging.

The shutter interval is shortened to 2 μs.

The sensor outputs a dedicated signal indicating the precise exposure trigger timing. This signal can be utilized for flash synchronization and other applications.