The power supply system for the DEPFET pixel detector at BELLE II

The upgrade of the KEKB accelerator towards 8×1035cm−2s−1 poses several challenges for the BELLE II detector. Especially the innermost detector will be faced with a significant radiation of several MRad per year as well as a high hit density. To cope with this a silicon pixel detector will be used for the inner layers of the silicon tracker.The pixel detector (PXD) consists of two layers of DEPFET active pixel sensors. The DEPFET technology has an unique set of advantages like low power dissipation in the active area, flexible device size, radiation hardness and a thinning procedure allowing to adjust the thickness of the device over a wide range. The two layers close to the interaction point together with a low material budget will improve the IP resolution by a factor of 2 compared to the previous installed silicon detector. In addition silicon stand-alone pattern recognition will be possible together with the four layers of double sided strip detectors (DSSD) of the strip detector.The PXD detector system consists of the DEPFET modules with integrated readout chips, the data handling hybrid receiving the data and sending them to compute nodes performing an online pattern recognition. Moreover the power supply system provides the supply voltages for the DEPFET from a position outside of the detector. The power distribution is designed to provide low output impedance over all frequencies and transient response with appropriate overshoots. The PXD pose several challenges to the power distribution system—number of voltages, tight requirements on regulation and noise.

► The KEKB accelerator receive a luminosity upgrade towards 8×1035cm−2s−1.
► A two layer pixel detector based on the DEPFET technology will be installed.
► An improvement of a factor of 2 in. impact parameter resolution is expected.
► The 34 A dedicated power supply system for the detector is under development which aims for low noise, low output impedance and a safe operation.