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Figure 31   Single and Two-Stage Amplifier Circuits
Logarithmic Meters

Instrumentation and Control 2 of 2
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Radiation Detectors CIRCUITRY AND CIRCUIT ELEMENTS Discriminator Circuit A discriminator circuit selects the minimum pulse height.  When the input pulse exceeds the   discriminator   preset   level,   the   discriminator   generates   an   output   pulse. The discriminator input is normally an amplified and shaped detector signal.   This signal is an  analog  signal  because  the  amplitude  is  proportional  to  the  energy  of  the  incident particle. The biased diode circuit is the simplest form of discriminator.  Figure 32 shows a biased diode discriminator circuit with its associated input and output signals. Figure 32   Biased Diode Discriminator Diode D1 is shown with its cathode connected to a positive voltage source +V.   A diode cannot 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 not conduct, 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 eliminate all pulses that are below the preset level.  The output pulses of this circuit have the same relative amplitudes as the input pulses. Rev. 0 Page 59 IC-06







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