ORTEC DSPEC Pro, Hardware User Manual

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794380D / 0914 1. INTRODUCTION
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Figure 1. Demonstration of the DSPEC Pro’s Minimum and Maximum Protection
Times in Enhanced Throughput Mode. At the maximum protection-time setting, the
DSPEC Pro processes pulses in the conventional way.
The digital filter in the DSPEC Pro measures the amount of charge collected for each event and
uses the result to increment the spectrum memory location associated with that charge measure-
ment. The Charge Trapping Corrector also measures the pulse rise time for the event. The pulse
rise time is used to adjust the very fine gain. For each pulse, the measured charge is increased by
the appropriate fine gain factor to correct for the signal lost due to carrier trapping.
1.4. The Low Frequency Rejector (LFR) Filter
In designing a multichannel buffer (MCB) that can be used in conjunction with mechanical
coolers, ORTEC has developed a new digital filter, the Low Frequency Rejector (LFR) filter,
capable of correcting the pulse output signal for changes in the baseline caused by cooler-
induced microphonics. In many ways digital filters are easier to understand than their analog
counterparts. Figure 2 shows the voltage step output produced at the preamplifier by the collec-
tion of charge produced by absorption of a gamma-ray and the resulting trapezoidal weighting
function in a digital spectrometer. The difficulty in the measurement is to precisely determine
the height of the step pulse because the baseline contains noise. A fairly obvious estimate of the