Ge detector preamplifier output signals tend to produce an overshoot at the beginning of the signal as shown in the scope screenshot below. This overshoot may vary in amplitude even for a fixed energy. A variation of the extracted energy is the result whenever the maximum of the flat top is used, as the overshoot will also reflect in an overshoot in the energy moving window (MW) .
The drawing below illustrates the difference between the use of the maximum energy value and the pickup energy index. The use of the pickup energy value will result in better energy resolution for cases with varying signal overshoot.
Note: The use of CFD triggering is recommended in combination with the energy pickup index functionality to minimize trigger jitter with induced jitter of the pickup point in time on the flat top of the energy MW.