Rolling Shutter Image Sensors
Rolling Shutter devices start and then stop their exposure line by line. This means that that each line will be recorded at a slightly different exposure time. This effect is pronounced for short exposures which produces images with distortion due to moving objects and short flashes of light.
This imaging behavior is typically outweighed by their increased sensitivity and lower cost as a result of the Rolling Shutter pixel design. This is the most common type of CMOS sensors and are found in products covering all markets.
Front Side Illuminated (FSI) Sensors
In FSI CMOS sensors, the pixel structure is built on top of the silicon wafer with the light sensitive photodiode at the bottom. On top of this, the various layers of wiring required to connect the pixels to the rest of the sensor are stacked up. The color filter and micro lens are then placed above everything. These are optimized to allow the collected light to pass down to the photodiode. However, this ‘height’ reduces the amount of light that will reach the photodiode due to scattering as well as from the reduced angles that the light can be accepted from. As pixels sizes are reduced this effect increases as the wiring cannot scale as easily as the features in the silicon.
Back Side Illuminated (BSI) Sensors
BSI sensors are created with the wiring layers below the photodiode thus reducing the height of the pixel stack while allowing for more light, from a larger acceptance angle, to be collected. Without the wires above the photodiode as with FSI sensors, the pixel pitch can be reduced more easily without impacting any of the necessary wiring.
With the wiring layers below the pixel, it is also possible to connect to another silicon layer thereby reducing the 2D footprint through stacking the sensor.
BSI is the industry standard for small pixels with both rolling and global shutter technologies. The better light collecting capabilities are apparent with their increased acceptance angles, color rendition and reduced pixel to pixel cross talk as a result of their reduced scattering.
Sony’s STARVIS Technology
Video systems for the surveillance of dark scenes require clean images with fine details and high contrast, despite low light levels. Sony’s STARVIS image sensor series is the result of world-class semiconductor engineering that is designed to fulfil the requirements of low light surveillance.
It features unprecedented sensitivity in a compact format and high resolution. These characteristics were created based on a new pixel architecture. Even in moonlight, STARVIS sensors enable imaging with low noise and wide dynamic range.
The resident broadcasting image quality allows both the imaging software and the control room staff to accurately analyze the video stream.
STARVIS backside-illuminated sensors with the rolling shutter feature a sensitivity of 2000 mV or more per 1 µm2 (color product, when imaging with a 706 cd/m2 light source, F5.6 in 1 s accumulation equivalent). They can reach an SNR of 1 already at 0.13 lux under Sony’s proprietary sensitivity index, SNR1s. For reference, a full moon on a clear night creates an illuminance on surfaces of 0.05 to 0.3 lux. Near-infrared enhanced models are also available to further improve image intensities for security applications using NIR lighting, for example.
STARVIS sensors provide resolutions from 2 MP to 61 MP. With pixel pitches starting from just 1.45 μm, a 4K resolution sensor gets as compact as 1/2.8 in optical format. Frame rates of up to 120 fps ensure a high resolution in the time domain, needed for smooth displays or detailed analysis. Sensor interfaces like MIPI CSI-2, sub LVDS, and SLVS-EC facilitate camera integration.
The most essential characteristic required for security cameras is a high degree of sensitivity. Now for the first time, a back-illuminated pixel developed specifically for security cameras has resulted in an outstanding improvement in sensitivity over our previous product structures, with light as bright as 0.5 lux. With the given combination of sensitivity, compactness, resolution, and speed, STARVIS is the first choice for low light surveillance.
Sony’s STARVIS 2 Technology
The STARVIS 2 is back-illuminated pixel technology used in CMOS image sensors for security camera applications. It features a sensitivity of 2000 mV or more per 1 µm2 (color product, when imaging with a 706 cd/m2 light source, F5.6 in 1 s accumulation equivalent). It also has a wide dynamic range (12 bit AD) of more than 8 dB as compared to STARVIS for the same pixel size in a single exposure. It achieves high picture quality in the visible light and near infrared light regions.
Sensor Functions and Features
DOL-HDR: Digital Overlap High Dynamic Range
Digital overlap HDR (DOL-HDR) delivers the data from multiple exposures on a line-by-line basis rather than frame by frame, reducing HDR combination artifacts. This improves picture quality, especially under poor light conditions, compared to multi-exposure HDR. DOL–WDR function requires a dedicated image signal processor to control the sensor and process the incoming images. However, DOL–WDR can provide many advantages such as improved characteristics in low-light environments compared to conventional WDR that uses multiple frames.
Part of what makes this method special is that the sensor can extend the integration time of the dark image (the long exposure one) so that it consumes the unused integration time of the previous short exposure frame to capture more light and information. This extends the dynamic range that can be presented into the subsequent HDR images, adding more detail, and improving the low-light response.
High Dynamic Range (HDR) Movie Function
Stacked CMOS Image Sensor
PDAF: Phase Detection Auto Focus
PDAF function is the high-speed auto focus technology. This technology has these merits compared to conventional contrast-based Auto-Focus: PDAF provides amazingly quick and accurate focusing with every frame detection; permits enhanced focusing with fast moving objects; and, enables rapid focusing with different subject positioning and ranges. The rapid calculation of the phase differences in the data between frames is the key to the performance of Sony’s proprietary PDAF technology.
Custom Rolling Sensor Options
Looking for custom design, semi-custom sensors, or design services?
Our partner, Pyxalis, is there to help with unique offerings and key technology differentiations to create a sensor that is one of a kind. Their sensor designs leverage their many years of experience in the field of image sensor development with competencies in pixel designs, Analog and Digital designs, product characterization, and product industrialization and qualifications.
Want to learn more details about our custom RS options? – Check out our complete portfolio of Pyxalis sensors.