IMAGE SENSORS
CMOS takes charge
Greg Blackman on the advances being made in image sensor technology for machine vision, including Sony’s first global shutter CMOS sensor
I
n the industrial and scientific imaging sector, there always used to be a battle between CCD sensors, where image quality ruled, and CMOS,
for higher frame rates. Tis is a fight that CMOS seems to be winning, although there are areas in astronomy and life sciences where CCDs are still the only option. All the major suppliers of industrial image sensors are offering advances in their sensor technology, but Sony has released a sensor that combines aspects of both CCD and CMOS in a pixel design, with some impressive performance specifications. Te Sony Pregius sensors are Sony’s first
global shutter CMOS sensors – global shutter is considered important for industrial vision as it avoids distortion. Daniel Diezemann, senior vision consultant at IDS Imaging Development Systems, described the architecture for the IMX174 sensor, part of the Pregius family, as ‘like a CCD pixel in a CMOS sensor’. ‘For 30 years, Sony has been the world’s major
supplier and manufacturer of CCD sensors. Sony now brings this knowledge to its new pixel design for the CMOS IMX174 sensor,’ he remarked. Te IMX174 has an analogue pixel design
similar to a CCD, with the back end basically a CMOS, explained Diezemann. Te sensor has the advantages of the CCD pixel – good colour reproduction, good performance, low noise, and high dynamic range with full well capacity – along with all the digital advantages of a CMOS device, so analogue-to-digital converter (ADC), image correction, and the digital output and high speed. ‘You will never achieve this frame rate with a
CCD sensor,’ commented Diezemann. Te 1,920 x 1,200-pixel resolution IMX174 offers a frame rate of 162fps. He added: ‘I’ve never seen such a good image from a consumer market sensor than with the Sony IMX174. We measured it with the EMVA1288 camera measurement standard in our optic labs and it is far superior in terms of measurement data compared to most other
comparable sensors. Tere is a really huge gap between them. Sony has really mixed up the market with this new sensor.’ High praise indeed, but it is borne out by some
impressive EMVA1288 specifications for the sensor – quantum efficiency at 525nm is 76 per cent for the 2.3 megapixel IMX174, dynamic range is 73dB, and the sensor has a low temporal dark noise of seven electrons meaning more signal gain without compromising image quality. ‘By implementing analogue memory at the pixel, Sony has reduced temporal dark noise to levels comparable to a CCD,’ commented Paul Kozik, product manager at Point Grey, which uses the new Sony IMX174 sensor in some of its Grasshopper and Blackfly camera models. Tere are, however, other important sensor
criteria for industrial imaging, noted Dr Lou Hermans, COO of sensor company Cmosis. He said that the global shutter and low dark noise of the Sony sensor was an advantage for machine vision,
18 Imaging and Machine Vision Europe • February/March 2015
but that other performance parameters such as frame rate, signal-to-noise ratio and near-infrared sensitivity were also key specifications. In addition, there are advantages to having
a family of sensors offering standard sizes and electronics to make it easy for camera manufacturers to integrate different sensors into their cameras. Tad Smith, director of business for image sensor products at On Semiconductor, commented: ‘IMX174 can indeed be considered a disruptive technology. Te technology demonstrates the possibilities of the new charge-based pixel approach and sets a new benchmark for image quality. ‘However, while IMX174 is a single part in the
portfolio, On Semiconductor’s image sensors offer a larger range of solutions for the industrial market. Tis is a key differentiator. Each of our customers is looking to streamline their own development and find synergies between sensors. Our platform approach, added with a single PCB solution
@imveurope
www.imveurope.com
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