NIM Model 620D 8-Channel Discriminator With Veto and Summing Output

The LeCroy Model 620D is an economy 100 MHz octal discriminator. Its common Inhibit and Summing Output make it a versatile instrument for a variety of physics applications. The 620D is based upon the Model LD601, a hybrid discriminator front end which is used in many of the popular LeCroy high energy physics discriminators.

The 620D offers a low minimum threshold of -30 mV, which is continuously variable up to -1 volt via front-panel screwdriver adjustment. A threshold monitor point is provided to permit the measurement of the threshold level with a common voltmeter. The stability of the threshold is <0.2%/'C to assure accurate results in varied operat- ing environments. The low input reflections of <4% provide substantial protection against multiple-pulsing due to reflections, a special necessity when working with low thresholds.

Designed to operate at maximum CW rates in excess of 100 MHz, the 620D offers a double-pulse resolution of 9 nsec and a propagation delay of 7.5 nsec. These discrimi- nators are non-updating, requiring that the output returns to zero before retriggering can occur.

The discriminator outputs are low impedance voltage outputs providing output levels greater than -800 mV into a 50 Ohm load. The output durations are presettable via front- panel screwdriver adjustment from 5 nsec to 20 nsec. Output risetimes and falltimes are <2.5 nsec.

A front panel summing output supplies a current pulse of -2 mA amplitude and 2.5 nsec risetime for each discriminator output which is in the logical 1 state. This feature may be used for multiplicity logic decisions in hodoscope systems, lead glass, or scintillator arrays.

The Model 620D has a built-in front-panel fast veto input which permits all channels in common to be inhibited for the duration of the veto signal. Veto must overlap the leading edge of the signal to be inhibited and must precede it by approximately 5 nsec.

   SPECIFICATIONS
   NIM Model 620D
   8-CHANNEL DISCRIMINATOR
  WITH VETO AND SUMMING OUTPUT

 INPUT CHARACTERISTICS

 Signal Input:  Threshold -30 mV to approximately -1.0 volt, (common to all chan-
   nels); front-panel screwdriver adjust (screwdriver included); 50 Ohm +/-1%,
   protected to +/-5 A for 0.5 usec clamping at +1 and -7 volts; reflec-
   tions <4% for input pulses of 2 nsec risetime; stability <0.2%/'C to
   60'C operating range; offset 0 +/-1 mV; threshold monitor 10:1 ratio of
   monitor voltage to actual voltage.
 Bin Gate:   Slow gate via rear connector and read panel ON-OFF switch; risetimes
   and falltimes approximately 50 nsec; clamp to ground from +5 inhibits;
   direct-coupled.
 Veto Input:  One; requires fast NIM-level signal (> -600 mV); 50 Ohm; must overlap
   leading edge of signal to be inhibited, and must precede input by
   approximately 5 nsec.


 OUTPUT CHARACTERISTICS

 Logic Outputs:  3 NIM-level voltage outputs, quiescently 0 volts, -800 volts during
   output; duration: 5 nsec to > 20 nsec, continuously variable via front-
   panel screwdriver control (narrower minimum width possible at slight
   expense of amplitude), risetimes and falltimes typically 2.0 nsec (max.
   2.5 nsec) 10% to 90%. Width stability better than +/-0.2%/'C maximum.
   At least 2 outputs should be terminated in 50 Ohm for optimum pulse
   shape.
 Summing Output:  A front-panel summing output supplies a 2.5 nsec risetime current pulse
   of -2 mA amplitude for each output which is in the logical 1 state.
   Although this output is a current source, it cannot be cascaded (wire
   ORed with other summing outputs) since it is internally back-terminated
   in a complex impedance. For optimum waveshape in fast decision logic
   applications all normal outputs must be terminated in 50 Ohm. Output
   widths should be set to >=10 nsec for multiplicity detection > 3. Input-
   to-"OR" output delay, 8 +/- 1 nsec.


 GENERAL

 Maximum Rate:  >100 MHz, input and output.
 Double-Pulse Resolution:  Less than 9 nsec at minimum width setting.
 Time Slewing:  1 nsec for input amplitudes 100% of threshold and above.
 Input-Output Delay:  7.5 nsec nominal
 Multiple-Pulsing:  None; one and only one output pulse of preset duration is produced for
   each input pulse, regardless of input pulse amplitude or duration.

 Packaging:   In RF-shielded AEC/NIM #1 module (AEC Report #TID-20893); Lemo-
   type connectors.
 Current Requirements:  +6 V at 220 mA -6 V at 575 mA
   + 12 V at 50 mA - 12 V at 160 mA
   +24 V at 0 mA -24 V at 45 mA