Due to the severe space limitation imposed by the environment the
preamplifiers are designed as integrated circuits.
The chips have been developed in the AMS 1.2 
CMOS process. Each chip
contains 6 preamplifiers consisting of a charge sensitive amplifier
followed by a shaper and output buffer. The shaping time is 200 ns.
In addition an on chip calibration is provided.
To be able to trigger with the calorimeter the chip can also provide the
sum of the signals of all 6 channels. The summing of individual channels
is programmable. The summed signal is shaped faster with a shaping
time of 90 ns to obtain the time resolution needed to identify the
bunch crossing to which the event belongs. The bunch crossing time at HERA
is 96 ns.
The preamplifier features affecting the calorimeter performance most are linearity and noise. The linearity was found to be better than 1 %. The noise of the preamplifier is a function of the capacitance connected to its input. The measurement of the noise in dependence of the input capacitance can be seen in figure 2.
Figure 2: Preamplifier noise as function of the input capacitance.
The actual capacitance connected to the preamplifier input is the photodiode capacitance which is approximately 10 pF. This results in a preamplifier noise of 420 electrons.