  A novel design for a silicon-tungsten electromagnetic calorimeter is
described, based on Monolithic Active Pixel Sensors (MAPS). A test sensor with
a pixel size of 50x50 um2 has been fabricated in July 2007. The simulation of
the physical sensor is done using a detailed three-dimensional charge spread
algorithm. Physics studies of the sensor are done including a digitisation
algorithm taking into account the charge sharing, charge collection efficiency,
noise, and dead areas. The influence of the charge sharing effect is found to
be important and hence needs to be measured precisely.
