Performance of the Domino Ring Sampler in the MAGIC experiment

We present a waveform digitizing system based on the Domino Ring Sampler (DRS) chip and its implementation in a mezzanine card. This system is suitable for experiments in which the waveform sampling of high-speed PMT signals is crucial. The analog waveform is stored in an array of 1024 capacitive sampling cells fabricated in a 0.25μm CMOS process and is read out at 40MHz with an external 12 bit flash ADC. The DRS sampling frequency can be chosen between 1.5 and 4.5GHz and is locked to an external low-frequency reference clock. The design is optimized for a multi-channel board with parallel sampling of 32 input channels triggered by a common pulse.In November 2004 the system was tested in La Palma on the magic telescope experiment and a preliminary measurement of the night sky background was performed. This is the first of a series of measurements that we are scheduling for a better understanding of the telescope performance.