583B Constant Fraction Differential Discriminator / Single Channel Analyzer

When operated in the Differential Mode, the Model 583B is ideal for use with fast scintillators and photomultiplier tubes. The dual discriminator levels allow this unit to function as a fast single-channel analyzer (SCA) in a fast-timing coincidence system, thus eliminating the need for separate slow-energy side channels. When used in the Integral Mode, the Model 583B is ideal for use with large-volume HPGe detectors and silicon charged-particle detectors operated in the traditional fast/slow coincidence system.

The input constant-fraction circuit uses a transformer and passive circuit pulse shaping technique to achieve better walk performance. It also provides a Monitor Output signal that is a linear representation of the constant-fraction shaped signal. This greatly simplifies the walk adjustment for optimum timing.

The use of surface-mount circuits in the Model 583B has greatly improved the time resolution obtainable at wide dynamic range when using fast scintillators.

An additional benefit of the Model 583B is that it can greatly improve the data rate capability of a timing experiment. The energy selection and coincidence decisions can be made before the time-to-amplitude conversion. This means the time-to-amplitude converter (TAC) must provide conversions only at the true coincidence rate rather than at the much higher single-event rate. Thus, high-count-rate problems in the TAC circuit are significantly reduced.

At the same time, the Model 583B provides simple and convenient operation. Only a few adjustments are needed for normal operation. The upper- and lower-level discriminators set the energy window for energy selection. The Integral/Differential switch determines whether the unit is to be used as a fast SCA or as an integral discriminator. The Constant-Fraction/ Slow-Rise-Time Reject control gives the user the flexibility to achieve good timing even where some relatively slow-rise-time signals are present. An adjustable output pulse width is provided to prevent multiple triggering on scintillation detectors with long decay times, such as NaI(Tl). The external Constant-Fraction Shaping Delay and Walk Adjustment should be optimized for each application.

Performance

Input Pulse	Accepts negative input pulses from 0 V to –10 V without saturation; input protected against overload; reflections ≤10% for input rise time ≥2 ns.
Discriminator Ranges	• Upper Level  –30 mV to –5 V. • Lower Level  –30 mV to –5 V.
Threshold Integral Nonlinearity	≤±0.5% of full scale.
Threshold Instability	≤±0.1 mV/°C, 0 to 50°C.
Time Walk	≤±75 ps for 100:1 dynamic range; Integral Mode, with external shaping delay ~2 ns, input rise time ≤1 ns, input pulse width ~10 ns, threshold = 30 mV
Propagation Delay	Nominally 18 ns, with external shaping delay ~2 ns.
Block Width	Variable from ≤15 to ≥1000 ns.
Minimum Pulse Pair Resolution	~50 ns for input pulse width ≤10 ns, or pulse width at the arming threshold +40 ns for input pulse width ≥10 ns.

Model	Description
583B	Constant-Fraction Differential Discriminator/SCA