Time Resolution of a Few Nanoseconds in Silicon Strip Detectors Using the APV25 Chip

The APV25 front-end chip for the CMS Silicon Tracker has a peaking time of 50 ns, but confines the signal to a single clock period (=bunch crossing) with its internal “deconvolution” filter. This method requires a beam-synchronous clock and thus cannot be applied to a (quasi-) continuous beam. Nevertheless, using the multi-peak mode of the APV25, where 3 (or 6,9,12,...) consecutive shaper output samples are read out, the peak time can be reconstructed externally with high precision. Thus, offtime hits can be discarded which results in significant occupancy reduction. We will describe this method, results from beam tests and the intended implementation in an upgrade of the BELLE Silicon Vertex Detector.