Innovative ams chip for X-ray detection heralds new era of lower-cost CT medical imaging

ams (SIX: AMS), a leading worldwide supplier of high-performance sensor solutions, is helping to make computed tomography (CT) scanners substantially more affordable. Through ams expertise in sensor design and packaging, the AS5950 integrated sensor chip for X-ray detection will enable an improved CT detector for more detailed images at lower system costs.
The AS5950 is a CMOS device that combines a high-sensitivity photodiode array and a 64-channel analog-to-digital converter on the same die. As a single chip, the AS5950 is easier to mount in a CT detector module. Current CT scanner manufacturers need to assemble a discrete photodiode array on a complex PCB, connected via long traces to a discrete read-out chip. In 8- and 16-slice CT scanners, replacement of this complex PCB assembly with a single AS5950 chip dramatically reduces the image-noise performance and – importantly – manufacturers’ materials and production costs.
Jose Vinau, Marketing Director for the Medical & Specialty Sensors business line at ams, says: “ams wants to help make CT scanners more affordable and available throughout the world. The introduction of the AS5950 and its module will reduce the hurdles in assembly and manufacturing of an X-ray detector.”

Innovation fuels market growth

ams estimates that the medical imaging market – for 8- and 16-slice CT scanners – is expanding at a compound annual growth rate of 10-15%.
ams’ innovation in integrating photodiodes and ADCs in a single chip will help make 8- and 16-slice CT scanners more financially viable for medical equipment buyers, helping drive up demand and accelerate the growth of the market.
The AS5950 comes with an optimum pixel size of 0.98×0.98 mm². However, this can be customized upon request to suit the OEMs specific needs within a reasonably short lead-time.
The sensor can be directly assembled on a substrate using a wire bonding process for manufacturing of a CT module. ams developed with partners the AS5950M, a CT module reference design that simplifies the integration into a complete CT detector. This two-side buttable module has either 2×2 pcs of AS5950 assembled on one substrate to build a sensor area of 32 x 16 mm² or 2×4 pcs of AS5950 for a sensor area of 32 x 32 mm².

Computing of sharper medical images

The AS5950’s integrated architecture improves image performance as the optimized wafer-level interconnects between the photodiode array and the read-out circuit allow much lower noise than the board-level traces in a discrete photodiode/ADC assembly. This results in:

• Improved image quality. Noise in high-resolution mode is typ. only 0.20 fC for a charge full-scale range of 455 pC. The ADC linearity of ±300 ppm and the compound linearity of ±600 ppm (including the photodiode) contribute to high image fidelity.
• Reduced self-heating. The very low power dissipation of typ. 0.65 mW per channel enables manufacturer to implement low-cost air cooling of CT scanners. An integrated temperature sensor enables monitoring of the junction temperature.

The AS5950 also offers fast integration time of as little as 200 µs, to support high scanner rotation speed. The digital data readout can be accessed via SPI interface that also allows to configure the following settings:

• Active sensor area. The total sensor dimension in Z-direction can be selected between 16 mm or 32 mm because of its three-side buttable concept.
• Pixel resolution. The adaptive array allows to operate the device in either high-resolution mode with a standard pixel size of 0.98×0.98 mm or in large Z-coverage mode connecting two pixels to a total size of 1.96×0.98 mm.
• Full scale range. Depending on the applied dose of radiation, the maximum photodiode current can be configured between 200 nA and 600 nA through three full scale ranges.

The AS5950 sensor IC as well as the AS5950M reference module are available for sampling now. An evaluation kit is also available to interface the sensor as well as the module reference design. It comes with a FPGA board and a software to demonstrate all relevant performance parameters.
For more detailed technical information, go to https://ams.com/as5950.