A 128 channels analog readout chip ($APVD_{DC}$) for DC-coupled silicon detectors of the CMS tracker

The APVD_DC realised in the DMILL technology is a radiation-hard integrated circuit for front-end readout electronics of the silicon tracker of CMS. DC-coupled silicon microstrip detectors have significant economical advantages compared to AC-coupled devices mainly due to their less complex fabrication process and better yield. The APVD_DC allows the use of DCcoupled silicon detectors with significant leakage currents as it is expected due to irradiation after several years of LHC operation. In this paper, a solution is presented with an active individual leakage current compensation technique for each input channel. The APVD_DC contains 128 identical analogue channels, each one composed of a low noise preamplifier, a CR-RC shaper, a 160 cells-deep analogue pipeline and an analogue signal processing stage. A deconvolution filter at the latest stage recuperates the initial fast response function of a silicon detector and confines it to one LHC bunch crossing. The 128 analogue channels are readout by a serial output via a high-speed analogue multiplexer. Slow control is implemented on the chip using an I2C serial bus, which allows to bias, to configure the chip and to run the internal calibration system. A current compensation circuit is added in front of every preamplifier to sink the leakage current coming from the detector. Good performance of the circuit has been measured on prototypes for leakage currents between 0 and up to 10 A.