AMS OSRAM, a leader in optical solutions, has introduced the AS5911, a 256-channel analog-to-digital converter (ADC) for digitizing signals from photodiode arrays in high-performance computed tomography (CT) scanners.

“The AS5911 is superior across the board in the domain of specialist ADCs for high-end CT detectors today, smaller, lower-power, high performance, more integrated, and easier for system designers to work with. Use of the AS5911 reduces complexity for manufacturers of CT detector modules of a plurality of form factors, including 4-side buttable CT detectors. It provides best-in-class power to noise performance to achieve highest image quality of next generation CT scanners. This helps medical practitioners to improve diagnostic value, and it ultimately leads to better outcomes for patients,” explained its developers.

Source: AMS OSRAM

The AS5911, housed in a 14 mm x 14 mm fine pitch ball grid array (FBGA), is a system-in-package solution that performs simultaneous current-to-digital conversion of the outputs from 256 photodiodes in a CT detector.

Smaller than current competing specialist ADCs for CT detectors, the AS5911 has a reduced footprint that facilitates its integration in a variety of detector form factors, including four-side buttable solutions thanks to its reduced external bill of materials (BOM) and embedded components. The AS5911 leads to lower system complexity by having integrated LDO voltage regulators, reference voltages, a temperature sensor, supply decoupling capacitors and on-chip calibration features.

The power dissipation is an additional benefit of the AS5911. At just 1.25 mW per channel in low-power mode, it consumes less power than existing products on the market. Its low power consumption facilitates temperature stabilization strategies by CT scanner manufacturers, ultimately yielding better system performance and potential savings in thermal management.

The AMS OSRAM proprietary ADC architecture, which features zero dead time, exhibits an excellent power-to-noise trade off. In low-noise mode, the input-referred noise is below 0.29 fC at an input current range of 0.5 µA. Low noise is a hallmark of high-performance CT detectors, a critical aspect for image quality, specifically at low X-ray dose.

The AS5911 features on-chip calibration functions for parameters such as offset voltage, linearity, offset charge and leakage current. This allows it to automatically set the photodiode and the front-end at their ideal operating point, compensating for offsets and non-linearities of the signal chain. The embedded auto-calibration functions reduce development effort in the data acquisition system and potentially enable the use of a lower-cost field-programmable gate array requiring less computational power.

The reduction of complexity of CT detector module design is also supported by features such as built-in diagnostics and the freedom to operate the device in two different power supply strategies. The device can operate in true ground mode and single analog supply. Full-scale range, power modes and digital readout features, are configurable over an SPI-compatible serial interface, as well as the data output modes of the digital low-voltage differential signaling interface.

For more information, visit the AMS OSRAM website.