A zero suppressing 200 MSPS waveform digitizer for MACRO

A 500 channel 200 mega samples per second (MSPS) zero suppressing waveform digitizer (WFD) is being built for the liquid scintillator system of the MACRO experiment. The WFD system will be used to search for slow moving magnetic monopoles requiring it to be able to store extremely long records of mostly zero data. To do this, it stores only data above a programmable threshold, along with a time word indicating when it was acquired. Each WFD channel has four inputs, each with an independent discriminator. The inputs are also summed and fed into an 8-b flash analog to digital converter (FADC). A nonlinear amplifier will be used to expand the dynamic range to the required 10-11 b. A CAMAC version of the WFD has been tested on the MACRO experiment in Italy. The final VME based version is now undergoing layout. To improve manufacturability and minimize power consumption, it will incorporate a GaAs gate array application-specific integrated circuit (ASIC).<>