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.
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.
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