Towards MYTHEN III - prototype characterisation of MYTHEN III.0.2

The MYTHEN detector is a single photon counting microstrip detector with 50 mu m pitch developed at Paul Scherrer Institute for powder diffraction experiments at the Swiss Light Source. After more than ten years of operation of MYTHEN II, a new readout chip MYTHEN III was designed in 110 nm UMC technology to upgrade the current detector. It is designed to improve all aspects, specifically noise performance, count rate capability, threshold dispersion and frame rate. Each strip in the MYTHEN III chip features a dual polarity front end consisting of a charge sensitive amplifier and a shaper with variable gain and shaping time, as well as three comparators and three gateable 24-bit counters. The internal counting logic allows for different modes of operation: energy-windowing, charge sharing suppression, count rate improvement and pump-probe with multiple time slots. The architecture of the chip and its characterisation results will be presented. The first two prototypes have been tested in the lab and at the synchrotron. The RMS noise is reduced to 178 electrons (-24% compared to MYTHEN II) and thanks to the three thresholds in the chip, we can detect multiple analog signals in the shaper at high photon flux and thereby reach a count rate of 25 MHz per strip. Based on these results, a full scale chip with 128 channels was developed and sent to production.