Pulse processing and Analyses

Dušan Kollár, 
DNP, FMFI UK Bratislava

Amplitude (Pulse Height) Measurements
Frequency and time response of amplifiers
  Application examples of operational amplifiers
  Transmission lines
Detector equivalent circuits
Nuclear detector analog signal processing
  Linear shape-amplifier
 ADC - digitization of pulse high
     DAC techniques
     ADC techniques
Timing measurement
     Fast time pick-off signal from input pulse
     Coincidence sytem
Time interval measurement

Amplitude (Pulse Height) Measurements

Integration on input capacitance

  • Determine energy deposited in detector
  • Detector signal generally a short current pulse
Typical durations:
Thin silicon detector (10 - 300 pm thick): 100 ps - 30 ns
Thick (~cm) Si or Ge detector: 1 - 10 ms
Proportional chamber (gas): 10 ns - 10 ms
Gas microstrip or microgap chamber: 10 - 50 ns
Scintillator + PMT/APD: 100ps-10 ms
Fig. m-1

Parameters of the detector output pulse.


The total charge QS contained in the detector current pulse is is proportional to the energy deposited in the detector

  • Necessary to integrate the detector signal current.
  1. Integrate charge on input capacitance.
  2. Use integrating ("charge sensitive") preamplifier.
  3. Amplify current pulse and use integrating ("charge sensing") ADC.
Fig. m-2 Example of first stage of pulse shaping - e.g. integrationon on input capacitance in ionisation chamber detector.

Fig. m-3Basic posibilities of the current integration:
  1. on input the RLCin chain of the preamplifier – voltage pulse is created and then amplificated;
  2. after current amplification is approached to integration with chain RC. The method is rarely used, but with such method high time resolution can bu reached.

Basic spectrometry system

Fig. m-4 A simple example, but complex system - e.g. in high energy physiscs - are often combinations of very many subsystems containing these base elements.
Fig. m-5
(pulse shape in point 1 on fig. above) (pulse shape in point 2a on fig. above)
(pulse shape  in point 2b on fig. above) (pulse shape in point 3 on fig. above)
Typical pulses which can be measured in system on fig. above.

Example of detector resolution

Spectra on figures down are collected from the same gama - source, but with diferent type of detector.
Fig. m-6 Ge detector

(Resolution expressed in absolute keV).

Fig. m-7 Scintillator NaI(Tl)
(Resolution -lower as in fig. left - is expressed as FWHM of single peak at specific energy).

Frequency response of linear amplifiers

Passive filters CR and RC
Amplifier pass band and feedback.
Transmission lines.

Problem how to design of amplifiers which give uniform gain and phase delay over the frequency pass - band. For example: pass - band in region:

    • 20 Hz - 100 kHz for audio amplifiers
    • 0 - 4,5 MHz for video amplifiers.
RC (resistance - capacitance) coupling amplifier are mostly used. Otherwise direct coupled amplifiers (in integrated form).

Most circuits for pulse shaping are based on the chain RC and transmission lines. Before proceeding to the subject of pulse processing I will deal briefly with the RC passive filters and with other interesting subject of transmission lines

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