AS5912

General description

Short Datasheet

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AS5912 512-channel low noise current-to-

digital converter

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General description

The AS5912 is an ultra-low noise, 512-channel low power current to digital converter that

enables the readout of photodiodes of a CT detector with highest sensitivity. The output

currents of 512 photodiodes are converted simultaneously into digital without any dead time

resulting in no charge loss on the inputs. The AS5912 combines current-to-voltage integration

and A/D conversion for 512-channels in one device. The ADC architecture with its low-noise

integrators, coarse quantizer, sample-and-hold and fine quantizer guarantee lowest input

related noise of maximum 0.29 fC (low noise mode) at an input current range of 0.5 µA. The

input current range of the ADC is selectable between 0.5 µA and 1 µA.

The AS5912 supports two supply concepts: a single analog and true ground supply, in both

modes the photodiodes are zero biased for ultra-low dark current of the photodiode. In true

ground mode, the AS5912 operates at ±1.5 V dual analog supply while in single supply mode

only a single analog supply of +3.0 V is needed. The device detects automatically the chosen

supply concept. No external components are required for supply decoupling. To reduce PCB

area and simplify the assembly process, decoupling capacitors for supply and reference

voltages are integrated in the 23 x 15 mm² FBGA package. The on-chip LDOs, reference

voltages and a temperature sensor minimize the external component requirements and

reduces the bill of material.

Full-scale range, integration time and power mode are configurable over a SPI-compatible

serial interface as well as the digital output modes of the LVDS interface. In low power mode,

the power dissipation can be minimized down to 1.25 mW per channel for reduced self-heating

of the CT detector. The adjustable integration time down to 51 µs allow very high frame rates.