The AS5950 is a sensor chip for 16-slice CT detectors that combines the photodiodes and the readout circuit on a single CMOS chip. This sensor solution, which includes an array of photodiodes with ultra-low dark current and a 64-channel ADC side-by-side, allows the assembly of the pixel array on three adjacent edges of the device. Two AS5950 ICs can be placed in Z-direction enabling the design of 16-slice detectors for cost optimized CT machines. The total sensor dimension in Z-direction is selectable between 16 or 32 mm, enabling two modes of operation. The adaptive array concept allows either a high resolution or a large sensor size on the detector. Pixel dimensions can be customized on request. The available standard product comes with a pixel dimension of 0.98x0.98 mm². The sensor can be directly assembled on a substrate using a wire bonding process for manufacturing of a CT module. Superior image quality can be achieved because the input-related noise is very low. In high-resolution mode a typical noise of 0.20 fC can be reached including the photodiode. This ultra-low noise figure is the result of the small capacitance of the photodiode, and the very low parasitic capacitance of the interconnect between the photodiode and its corresponding ADC channel. The low power consumption of typ. 0.65 mW per channel reduces self-heating effects and reduces the overall cost of cooling the system. The digital data readout can be accessed via SPI interface. It is also used to configure parameters such as pixel resolution, input current range, active sensor area and enabling the calibration mode. An integrated temperature sensor enables monitoring of the junction temperature. Featuring on-chip photodiodes, the AS5950 offers a cost-optimized solution and is delivered as die on foil.
The AS5900 device is a low noise, 128-channel current-to-digital converter that enables the readout of the photodiodes with highest sensitivity. High-resolution CT imaging can be achieved up to 26-bits resolution. Its 128-low-noise and high linear converter channels provide an increased gray scale, improved contrast and reduce artifacts of 3D CT images. The low power consumption of 1mW per channel reduces self-heating effects and the overall power consumption of the system. An integrated temperature sensor allows the calibration of temperature drifts of the X-ray detector modules.