Charge Sensitive Amplifier with Offset-Compensated V-to-I Converter for the Mini-SDD-Based DSSC Detector

In this article, we present the study and the experimental results of a charge sensitive amplifier (CSA) for the mini-silicon drift detector (SDD) pixel sensors of the DEPleted Field-Effect Transistor (DEPFET) sensor with signal compression (DSSC) detector for photon science applications at the European X-ray free electron laser (XFEL) GmbH in Hamburg area. The DSSC detector must be able to cope with an image frame rate up to 4.5 MHz and with a dynamic range up to 104 photons/pixel/pulse for a photon energy of 1 keV. These goals will be pursued with the adoption of the DEPFET detector strategy. For the first camera prototype, a simpler solution based on a mini-SDD array read out by a conventional CSA has been adopted. We present here the CSA solution with a very simple V-to-I converter stage, which allows the self-canceling of the offset current flowing between the CSA and the filter, without the need of an intermediate stage. The CSA is compatible with the same application-specified integrated circuit (ASIC) architecture and readout chain already designed for the DEPFET detector. We present two versions of the CSA: one with a linear response and another with a nonlinear output characteristic. The nonlinear version provides increased input dynamic range preserving single-photon sensitivity. The experimental measurements have demonstrated the functionality of the proposed self-canceling solution and good noise performance with an equivalent noise charge (ENC) of 65 e- rms at the 4.5-MHz frame rate and a linearity error lower than 0.25% of the complete channel. In addition, the functionality of the nonlinear version (signal compression version) of the CSA has been demonstrated, without penalty in noise performance in the linear region of the CSA response.