Optimized readout methods of silicon drift detectors for high-resolution X-ray spectroscopy

Silicon Drift Detectors with integrated FET transistor fabricated at Max-Planck-Institute in Munich in cooperation with PNSensor GmbH are widely used as X-ray sensors in many industrial and scientific applications. In the classical readout scheme, the integrated transistor on the SDD is operated in the source–follower configuration. The signal charge is removed continuously by the detector self-rest mechanism. The method gives very good results at counting rates up to 10 kcps. For higher count rates, the FWHM increases with the growing reset current and a slight shift of the energy peak is observed. The relative large signal rise time can be also a limitation for operation at very high count rates. Alternatively, the SDD can be operated in a Charge Sensitive Amplifier (CSA) configuration. The detector signal charge is integrated on a feedback capacitor across an inverting amplifier with the integrated FET as the input transistor. The signal rise time does not depend on the integrated transistor and can be made very short (e.g. 50 ns). In applications requiring very high counting rates and constant energy resolution, pulsed-reset operation of the SDD is desirable. The signal charge is removed by applying short reset pulses to a reset structure integrated on the detector anode. The combination of the CSA readout scheme and the pulsed-reset method allows the operation at the best energy resolution independent on the count rate.