Features

• Four CF discriminators in a
  single-width NIM
• 200 MHz count rate
  capability
• 1000:1 dynamic range
• Typical walk <±30 ps for 100:1
  dynamic range
• Selectable fraction or leading
  edge operation
• Output indicator LEDs
• Gated operation

Description

The CANBERRA Model 454 QUAD CFD combines four 200 MHz Constant Fraction Discriminators in a single-width NIM module. The proven constant fraction technique generates precision timing signals from fast negative input signals up to a 1000:1 dynamic amplitude range. Each discriminator exhibits typical walk of less than +30 ps for a 100:1 input amplitude range.

Each of the four independent discriminators has selectable fraction modules which can be exchanged for optimum performance with a particular PM tube or solid state detector. The 20% fraction module is supplied for each discriminator section. Other fractions are available as inexpensive options. The discriminators can be converted to a conventional leading-edge discriminator by use of the appropriate module, available from the factory. The delay required to internally generate the constant fraction timing signal is provided externally by the proper length
of cable across the delay connectors.

Each discriminator has a separate threshold adjustment and monitor (T), and walk adjustment and monitor (Z). Another output (Z/C MON) is available to allow monitoring of the internally produced zero-cross signal which coincides with the constant fraction timing mark.

Three independent fast negative outputs are provided for each discriminator. A width adjustment allows the output to vary from less than 5 ns to greater than 500 ns in two ranges. This allows compatibility with certain devices such as counters being driven by the 454 and prevents false triggering from trailing edge noise which can be encountered with certain detectors. A visual indication of discriminator activity is provided by an output LED.

Rear panel inputs allow each of the discriminators to be independently gated from an external source. Also a master BIN gate signal available on special NIM bins may be used to control the 454. Internal switches allow any combination of the discriminator sections to be controlled by the BIN gate.

The 454 is compatible with the NlM-standard type V-H bin and power supplies that include ±12 V and ±6 V.