LeCroy 621BL Quad Discriminator

NIM Model 621 BL Quad Discriminator With Burst Guard

The LRS Model 621 BL 100 MHz Quad Discriminator is a refinement of the widely used Model 621AL. Utilizing the same hybrid circuit front end (LD601 Series) as the 621 AL and largely identical circuitry, the 621 BL offers all the features of the 621 AL in addition to a switch-selectable Burst Guard mode. This feature allows the discriminator to respond to DC levels (approximate time-overthreshold) and to input pulses spaced less than the DPR of the device (<9 nsec).

In the Burst Guard mode, the output of the front end is OR-ed with the conventional mode output of the Model 621BL. Thus, for input pulses arriving at a rate which exceeds the double-pulse resolution of the unit, the discriminator output duration will be equal to the time interval between the first leading edge threshold crossing and the last trailing edge threshold recrossing, or the preset output width, whichever is greater. The Burst Guard feature is of particular utility for veto counters under high counting rate conditions. In the Update Only mode, the Burst Guard feature is defeated and the performance of the 621 BL is identical to that of the 621 AL.

The threshold of the 621 BL is variable from -30 mV to - 1 volt via front panel screwdriver adjustment. This low minimum threshold permits experimenters to routinely reverse-terminate photomultiplier anodes and, coupled. with the extremely low input reflections, greatly reduces the possibility of multiple-pulsing due to input reflections in the system.

Each channel of the 621BL provides 6 (five negative and one complementary) fast NIM-level current source outputs. Output durations are adjustable from 5 nsec to 1 usec in the Update Only mode and are independent of input amplitude, duration, and rate.

The Model 621BL is also available with the option to permit remote control of both threshold and output width via DC levels applied to a rear panel 20-pin connector. This option, which makes it feasible to remotely adjust for PM high voltage drifts, is characteristic of the Model 621 BLP and is described in detail in the 621 BLP technical data sheet. An additional factory option of high impedance bridged inputs at the expense of one normal output helps eliminate the necessity to run long cables from both the PM anode and dynode when the PM signals must drive both a discriminator and an ADC.

SPECIFICATIONS

NIM Model 621BL QUAD DISCRIMINATOR
With Burst Guard

INPUT CHARACTERISTICS

Signal Input:

Threshold, -30 mV to -1.0 volt; front-panel screwdriver adjustment (screw- driver included); 50 Ohm protected to +/-5A for 0.5 usec, clamping at +1 and -7 volts; reflections 4% for input pulses of 2 ns risetime; stability 0.20/o/Deg.C over 20Deg.C to 60Deg.C operating range; offset 0 +/-1 mV; threshold monitor has 10:1 ratio of monitor voltage to actual voltage.

Bin Gate:

Slow gate via rear connector and rear-panel ON-OFF switch; risetimes and falltimes, approximately 50 nsec; clamp to ground from +5 V inhibits; direct- coupled.

OUTPUT CHARACTERISTICS

Bridged Negative Outputs:

2 pairs; NIM; quiescently 0 mA, -32 mA during output; risetimes and falltimes (all outputs terminated in 50 Ohm) typically 2.0 nsec (max. 2.5 nsec), 1 0% to 90%. Output falltimes slightly longer on wide output durations. Width stability better than +/-0.20/o/Deg.C maximum.

Fast Negative Timing Output:

One; NIM; quiescently 0 mA, -16 mA during output. Other characteristics same as above, except risetimes are typically 1.5 nsec (max. 2.0 nsec), and minimum width is <=6 nsec.

Complementary Output:

One; quiescently - 1 6 mA, 0 mA during output. Other characteristics same as for Fast Negative Timing Output.

Duration:

Update Only Mode: 5 nsec to 1 usec, continuously variable up to 600 nsec via front-panel screwdriver control (narrower widths possible at slight expense of amplitude).
Burst Guard Mode: Output duration is approximately equal to the time-over- threshold of the input signal or equal to the preset duration, whichever is grea- ter. For input burst rates greater than the DPR of the unit, the output is equal to the duration of the burst or the preset width, whichever is greater.

GENERAL

Maximum Rate:

110 MHz typical, input and output.

Double-Pulse Resolution:

Less than 9 nsec at minimum output width setting.

Time Slewing:

1 nsec for input amplitudes 1 10% of threshold and above.

Input-Output Delay:

9.5 nsec typical.

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 450 mA;
+6 V at 150 mA;
-12 V at 165 mA;
+12 V at 20 mA;
-24 V at 85 mA.

High Impedance Option:

The Model 621 BL is also available with a bridged high impedance input (at the expense of one negative output) at additional cost.

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INPUT CHARACTERISTICS
Signal Input:	Threshold, -30 mV to -1.0 volt; front-panel screwdriver adjustment (screw- driver included); 50 Ohm protected to +/-5A for 0.5 usec, clamping at +1 and -7 volts; reflections 4% for input pulses of 2 ns risetime; stability 0.20/o/Deg.C over 20Deg.C to 60Deg.C operating range; offset 0 +/-1 mV; threshold monitor has 10:1 ratio of monitor voltage to actual voltage.
Bin Gate:	Slow gate via rear connector and rear-panel ON-OFF switch; risetimes and falltimes, approximately 50 nsec; clamp to ground from +5 V inhibits; direct- coupled.
OUTPUT CHARACTERISTICS
Bridged Negative Outputs:	2 pairs; NIM; quiescently 0 mA, -32 mA during output; risetimes and falltimes (all outputs terminated in 50 Ohm) typically 2.0 nsec (max. 2.5 nsec), 1 0% to 90%. Output falltimes slightly longer on wide output durations. Width stability better than +/-0.20/o/Deg.C maximum.
Fast Negative Timing Output:	One; NIM; quiescently 0 mA, -16 mA during output. Other characteristics same as above, except risetimes are typically 1.5 nsec (max. 2.0 nsec), and minimum width is <=6 nsec.
Complementary Output:	One; quiescently - 1 6 mA, 0 mA during output. Other characteristics same as for Fast Negative Timing Output.
Duration:	Update Only Mode: 5 nsec to 1 usec, continuously variable up to 600 nsec via front-panel screwdriver control (narrower widths possible at slight expense of amplitude). Burst Guard Mode: Output duration is approximately equal to the time-over- threshold of the input signal or equal to the preset duration, whichever is grea- ter. For input burst rates greater than the DPR of the unit, the output is equal to the duration of the burst or the preset width, whichever is greater.
GENERAL
Maximum Rate:	110 MHz typical, input and output.
Double-Pulse Resolution:	Less than 9 nsec at minimum output width setting.
Time Slewing:	1 nsec for input amplitudes 1 10% of threshold and above.
Input-Output Delay:	9.5 nsec typical.
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 450 mA; +6 V at 150 mA; -12 V at 165 mA; +12 V at 20 mA; -24 V at 85 mA.
High Impedance Option:	The Model 621 BL is also available with a bridged high impedance input (at the expense of one negative output) at additional cost.