  We present a study of a CMOS test sensor which has been designed, fabricated
and characterised to investigate the parameters required for a binary readout
electromagnetic calorimeter. The sensors were fabricated with several
enhancements in addition to standard CMOS processing. Detailed simulations and
experimental results of the performance of the sensor are presented. The sensor
and pixels are shown to behave in accordance with expectations and the
processing enhancements are found to be essential to achieve the performance
required.
