GANDALF — Design of a modular high resolution transient recorder for high energy physics

With present-day detectors in high energy physics one often faces short analog pulses with a typical length of a few nanoseconds length which may cover large dynamic ranges in amplitude. In many experiments both amplitude and timing information have to be measured with high accuracy. Additionally the data rate per readout channel can reach several MHz, which places strong demands on the separation of pile-up pulses. For such applications we have built the GANDALF transient recorder with a resolution of 12bit at a sampling rate of 1GS/s and an analog bandwidth of 500 MHz. Signals are digitized and processed by fast algorithms to extract pulse arrival times and amplitudes in real-time and to generate experiment trigger signals. With up to 16 analog channels, deep memories and a high data rate interface, this 6U-VME64x/VXS module is not only a dead time free readout system but also has huge numerical capabilities. These are provided by the implementation of a Virtex5-SXT FPGA, which is used to disentangle possible pile-up pulses and determine timing information with a time resolution in the picosecond range. Recently the application spectrum has been extended by implementing a 128-channel time-to-digital converter inside the FPGA in combination with an appropriate input mezzanine card.