microDXP Technical Reference Manual
Version 3.15
October 7, 2019
38
Figure 3-2: A saw tooth function having the same average slope as the preamp output, which
ranges from -3.0 V to -0.25 V, is subtracted from it and the difference amplified and
offset to match the 2.0 V input range of the ADC.
Occasionally, as also shown in Figure 3-2, fluctuations in data arrival rate will cause the
conditioned signal to pass outside the ADC input range. This condition is detected by the
FiPPI, which has digital discrimination levels set to ADC zero and full scale, which then
remedies the situation by quickly closing the reset switch. During this so-called
Tracking
Step
, data passed to the FiPPI are invalid. Preamplifier resets are detected similarly. Note:
Data acquisition is halted until the time period defined by RESETINT has expired (see also
§2.3.1.3).
3.2.1.2
RC-Feedback Preamplifiers
RC-feedback preamplifiers inherently produce a smaller dynamic range: At low rates the
preamplifier output decays to baseline after each event, producing a voltage range on the
order of a single event; at higher rates successive events add up, however, the larger the
sum, the steeper the decay slope back to baseline. The result, as of course intended, is to
yield a full-scale signal that increases only logarithmically with count rate.
