Preamplifiers

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Preamplifiers

The hybrid preamplifiers are mounted on boards carrying 27 channels at maximum.

**Figure 5:** Preamplifier scheme
$\begin{figure} \begin{center} \epsfig {file=gdh_pre.ps, width=13.5cm}\end{center}\end{figure}$

These boards provide for the detectors voltage supply. They are referred to a positive voltage for cathodes (n side) and to ground for anodes (p side).

**Figure 6:** Preamplifier differential output. A step pulse is injected into the test input of the preamplifier. The output of the preamplifier is shown without (up) and with (down) the detector capacitance.
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In fig. 5 the schematics of a single preamplifier channel is shown. The original design was slightly modified in order to increase the input capacitance and the linear range. The input stage consists of a FET with capacitance C $_{in}$ =35 pF. The differential output has a dynamic range of $\pm$ 400 mV and a gain of 1 mV/fC. The equivalent noise charge (ENC) is 230 e measured with no input capacitance.

In fig. 6 the output signals of the preamplifier are shown.

Next: FEMC modules Up: The Electronic Chain Previous: The Electronic Chain

Alessandro Braghieri
2001-04-10