Pulse processing and Analyses

	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

^Preamplifier

^{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 Q_S contained in the detector current pulse i_s is proportional to the energy deposited in the detector

Necessary to integrate the detector signal current.

Possibilities:

Integrate charge on input capacitance.
Use integrating ("charge sensitive") preamplifier.
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:

on input the R_LC_in chain of the preamplifier – voltage pulse is created and then amplificated;
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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