Radiation DetectorsCIRCUITRY AND CIRCUIT ELEMENTSDiscriminatorCircuitA discriminator circuit selects the minimum pulse height. When the input pulse exceedsthe discriminator preset level, the discriminator generates an output pulse. Thediscriminator input is normally an amplified and shaped detector signal. This signal isan analog signal because the amplitude is proportional to the energy of the incidentparticle.The biased diode circuit is the simplest form of discriminator. Figure 32 shows a biaseddiode discriminator circuit with its associated input and output signals.Figure 32 Biased Diode DiscriminatorDiode D1 is shown with its cathode connected to a positive voltage source +V. A diodecannot conduct unless the voltage across the anode is positive with respect to the cathode.As long as the voltage at the anode is less than that of the cathode, diode D1 does notconduct, and there is no output. At some point, anode voltage exceeds the bias value +V,and the diode conducts. The input signal is allowed to pass to the output.Figure 32 illustrates input and output signals and how the discriminator acts to eliminateall pulses that are below the preset level. The output pulses of this circuit have the samerelative amplitudes as the input pulses.Rev. 0 Page 59 IC-06
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