OVERVIEW

The LeCroy Model 4413 is a 16-input discriminator in a single- width CAMAC module. Three modes of operation are pro- vided; Updating, Burst Guard and Retiming Mode. The module accepts NIM level inputs and operates to 150 MHz. The out- puts of the 4413 are differential ECL levels which are compat- ible with LeCroy's ECLine series of programmable logic mod- ules. Output widths are adjusted from 3.5 nsec to 100 nsec in the Update mode.

Each of the 16 channels share a common threshold which is set by a front-panel potentiometer or via CAMAC commands. The threshold range extends from -15 mV to -1 V. The unit also has a common front-panel VETO input as well as a TEST in- put. However, the TEST mode can also be initiated by CAMAC commands and only desired channels may be tested using a CAMAC write mask command. In addition, the unit has two bridge outputs which generate a current proportional to the input multiplicity.

The high density is made possible through the use of eight HVL201 hybrids. These hybrids enhance the reliability of the Model 4413 as well as provide for the 150 MHz counting rate operation.

Input Characteristics Signal Inputs: sixteen inputs via Lemo front-panel connectors, 50 Ohm +/-2%, protected to +/-5 A for 0.5 usec, clamping at +/-5 V. Reflections <4% for input pulses of 2 nsec risetime. Stability better than 0.25%/'C to 60'C operating range. Offset +/-3 mV. Threshold: -15 mV to -1 V +/-5% or 5 mV, whichever is greater; front-panel screwdriver adjust in local or threshold 10-bit DAC in remote mode. Threshold Monitor: front-panel test point has 10:1 ratio of monitor voltage to actual voltage +/-5%. Hysteresis: typical 3.5 mV. Test Input: one input via a Lemo connector on the front panel, 50 Ohm +/-2%. Requires NIM level direct coupled signal (<-600 mV) to trigger all channels. Minimum width: 3 nsec. Maximum rate: 150 MHz. Veto Input: one input via a Lemo front-panel connector, 50 Ohm +/-2%, permits simultaneous fast inhibiting of all channels; requires NIM level signal (<-600 mV). Direct coupled. Must precede input signal by approximately 1 nsec and overlap its leading edge in Updating mode or overlap complete input signal in Burst Guard mode. Minimum duration: 3 nsec. Sync-Strobe Input: One Lemo front-panel connector, 50 Ohm +/-2%. Requires complementary NIM level signals. When using this input the Sync-Strobe pulse leading edge will deter- mine the output timing, while the output width will be deter- mined by the overlap of the unstrobed outputs and the Sync- Strobe pulse. Inputs to be retimed must precede Sync-Strobe pulse by 10 nsec minimum. Also, ensure that the width of the unstrobed discriminator output completely overlaps this pulse.

Output Characteristics Discriminator OutPuts: Two separate outputs per channel. ECL level (-0.8, -1.7 V) into 100 Ohm twisted pair. Duration, approximately 3.5 nsec to 100 nsec, continuously variable via screwdriver control, common to all channels. Risetimes and falltimes <2 nsec. Width stability better than 0.3%/'C maxi- mum. Current Sum Outputs: Two bridged, rear-panel, Lemo connec- tors; high impedance current source; generates a current propor- tional to the input multiplicity at the rate of -2 mA +/-10% per hit; 100 MHz maximum rate. The two connectors can be used for daisy chaining within a group of similar units.

 Output Operation Modes: Updating or Burst Guard operation
 selectable by rear-panel switch. Retiming mode active when
 using the Sync-Strobe input.



Timing
Characteristics

 Double Pulse Resolution: 5 nsec typical.
 The speed of a discriminator is practically defined by its double
 pulse resolution or the time between the leading edges of the
 most closely spaced pulse pairs for which the discriminator pro-
 duces two distinct output pulses. Although simple in concept,
 this specification can be misleading unless the input conditions
 are precisely defined and ambiguities in performance are dis-
 closed. One should indeed investigate the double pulse resolu-
 tion as a function of the input amplitude over threshold and of
 the input width.
 Tracking Error: Tests on the 4413 show a tracking error typi-
 cally not in excess of 200 psec.
 The ability of a discriminator to be used for precise timing (co-
 incidence or TOF) in an environment which encounters narrow
 pulse pair separations is demonstrated by considering the time
 shift (or tracking error) introduced as the time interval between
 successive inputs is reduced. In an experiment, tracking error is
 equivalent to time dispersion as a function of input rate. For
 many experiments, this can be critical, since it is often in high
 rate situations that the best timing resolution is required.
 Time Slewing: <500 psec for input amplitudes from 2 times to
 20 times over threshold. See Figure 2.
 Slewing is the variation in propagation delay from the beginning
 of the pulse input to the output pulse as a function of input
 pulse amplitude. The intrinsic slewing is measured as a function
 of input crossing threshold to output pulse. In addition, pulses
 of varying risetimes give different delays from the beginning of
 the pulse since the threshold crossing time relative to the pulse's
 leading edge depends upon the amplitude of the pulse. Only
 the intrinsic slewing is specified for the Model 4413 since
 risetime slewing is application dependent.
 Slewing is typically measured as the difference between propaga-
 tion delay for input pulse amplitudes twice that of threshold and
 input pulses whose amplitudes are 20 times threshold. Thresh-
 old is defined as the input pulse level which results in discrimi-
 nator firing for 50% of the pulses.


 General

Maximum Rate: 150 MHz.
Input-Output Delay: <18 nsec.
Test-Output Delay: <18 nsec.
Multiple Pulsing: None: one and only one output pulse is pro-
duced for each input pulse regardless of input pulse amplitude
and duration.
Sync-Strobe to Output Delay: 9 nsec +/-0.5 nsec
LED Indicators: Two front-panel LED's respectively indicate,
when lit, that programmable mode and Updating operation have
been selected.
Burst Guard-: A front-panel switch enables the Burst Guard
or Updating operation for all channels.
Power Requirements: +24 V at 0.03 A; +6 V at 1.3 A;
    -6 V at 4.1 A; -24 V at 0.03 A.


CONTROL AND
CONNECTORS

Signal Input

 Signal input to each of the 16 channels is made via a front-
 panel Lemo connector. The inputs of 4413 discriminator are
 protected to 5 A for 0.5 usec, clamping at +/-5 V.
 The DC protection is limited by the 0.25 W dissipation limit of
 the input resistor, which can be assumed to offer protection
 against DC signals less than 5 V.
 Input reflections for the 4413 are less than 4% with 2 nsec in-
 put pulses.



Threshold

 The threshold range of the 4413 Octal Discriminator is from
 -15 mV to -1 V and is adjustable by a front-panel, 15 turn
 potentiometer. Threshold is increased by turning this control
 clockwise. Alternatively, threshold can be programmed by
 CAMAC F(17) command. In either case, threshold is common
 to all channels and the adjustment is uniform and does not pre-
 sent any discontinuity or changes in sensitivity.
 A front-panel test point is a 10:1 monitor of the actual thresh-
 old value within +/-5%. The output impedance of the test point
 is 1 kOhm, so a high impedance digital voltmeter should be used.



 Test Input

 A rear-panel Test input allows all channels to be triggered once
 a negative NIM pulse is received. This useful feature allows
 complete testing of the module without removing any input cable
 and also permits the use of the 4413 as a 32-fold fan-out. The
 Test pulse will have the same effect as a similar pulse on the
 normal inputs. In particular, the output width in Burst Guard
 mode will be proportional to the input width.



 VETO Input

 A common front-panel Lemo input connector allows vetoing of
 all channels simultaneously, when a negative NIM pulse is ap-
 plied. A complementary NIM signal applied to the VETO input
 permits the 4413 to be used as an 16-channel strobed coinci-
 dence unit. In other words, the discriminators will only gener-
 ate an output when the input level exceeds the set threshold
 and while these signals occur during a logical 0 (>=-100 mV)
 state of the complementary input to the VETO.
 However, the action of the VETO input can be different de-
 pending on the operation mode of the unit (Updating or Burst
 Guard) and on the static level of the VETO input (see Figure
 3).
 Updating mode: In the Updating mode, the leading edge of
 the input pulse triggers the discriminator timing stage. A VETO




 Sync-Strobe Input

 A front-panel LEMO connector allows retiming of the output
 pulses which are not coincident in time, within a window de-
 fined by VETO and a common synchronization pulse. The
 Sync-Strobe input allows realignment of all output leading edges
 with the leading edge of the sychronization pulse to within
 +/-0.5 nsec. The Sync-Strobe Input requires complementary
 NIM signal levels.
 Inputs to the 4413 which exceed threshold and which are to be
 retimed must precede the Sync-Strobe pulse by 10 nsec mini-
 mum and should completely overlap this pulse to avoid variable
 width outputs. For more details see Chapter 4, Operating In-
 structions.



 Output

 The output of 4413 is differential ECL pulse pairs suitable for
 driving twisted-pair cables. Two outputs per channel are pro-
 vided from two 34-pin front-panel connectors.
 The output of selected channels in the TEST mode can be dis-
 abled or masked by loading a 16-bit word via CAMAC F(16)
 command into a storage register.



 Width Adjustment

The output width is common for each channel and is continu-
ously adjustable via front-panel potentiometer from 3.5 nsec to
>100 nsec in the Updating mode. Minimum width is set by
turning the potentiometer fully counter clockwise.
The main contributors to output width uncertainty are a function
of the external conditions. Variations in both temperature and
supply voltage can cause significant changes in output width.
Width temperature coefficient has been measured to be
<0.3%/'C while the voltage coefficient is negligible because of
the onboard stabilization of the current at -5.0 V.



Current Sum Output

 An analog signal which is proportional to the number of chan-
 nels which exceed the threshold is available via bridged rear-
 panel Lemo connectors. This analog majority information con-
 sists of 2 mA +/-10% per enabled channel for the duration of
 that channel (minimum of 10 nsec). When using only one con-
 nector with a 50 Ohm load, the voltage step is 100 mV/hit. When
 both outputs are used with 50 Ohm loads, the output is 50 mV/hit.
 The output amplitude is limited to a maximum of 1.6 V. The
 two connectors allow cascading of several units if needed. In
 this case, care should be taken to terminate the unused output
 to avoid reflectors. Figure 4 shows an example of the current
 sum output with only one load.


 Updating/Burst
 Guard Switch

 The module has a rear-panel switch which allows the selection
 of the operational mode. See Figure 5 for a comparison.
 Updating: In Updating mode, the output is extended if a sec-
 ond pulse arrives before the first output returns to zero, as long
 as the second pulse arrives at a time later than the double pulse
 resolution of the unit. Thus, the second pulse will be seen by
 the front end of the unit even though an output pulse is still
 present from the first signal. The second pulse will cause a new
 output to be generated and added (in time) to the portion of
 the original output already occurring.
 Burst Guard: In Burst Guard mode, the output of the front
 end is OR'd with the conventional mode output. For input
 pulses arriving at a rate which exceeds the double pulse resolu-
 tion 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. This feature is espe-
 cially important in veto applications when the discriminator
 output must be enabled as the detector is hit by unwanted and
 unmeasurable high rates.  A discriminator without Burst Guard
 would see the first pulse and generate the preset output width,
 but would be paralyzed at quiescent level or would trigger only
 randomly for subsequent pulses separated by less time than the
 DPR of the unit.  Burst Guard assures a logical 1 output level
 during these high rate bursts.

 Burst Guard mode is also useful in any application where the
 output width has to be proportional to the input width.



 CAMAC Commands


 Z: Clears mask register at S2 time, sets module into Local
 mode.
 N-F(O)-A(O):  Reads mask register.  Q response in Remote
 mode only.
 N-F(l)-A(O): Reads threshold setting when in Local or Remote
 mode.
 N-F(16)-A(O):  Writes mask register pattern (Wl-W16).  Exe-
 cutable and Q response generated in Remote mode only.
 N-F(17)-A(O): Writes threshold setting register; 11 bits, 10 bits
 of data (W1-W10) providing 1 mV resolution are used to pro-
 gram common threshold and 1 bit (Wll) to set the manual
 threshold value (front-panel screwdriver control) to the thresh-
 old register.
 In this case, the data presented on Wl-W10 is ignored.  Exe-
 cutable and Q response generated in Remote mode only.
 N-F(25)-A(O): Test function.  Only channels not masked off by
 F(16) are triggered by internally generated 3 nsec wide pulse.
 Executable and Q response generated in Remote mode only.
 N-F(24)-A(O):  Set Local mode.
 N-F(26)-A(O): Set Remote mode.



 CAMAC Responses



  X: An X=1 response is generated for every valid F,N,A.
  Q: A Q=l response is generated if the valid command can be
  executed.