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A clocked, fast electronics trigger for high energy physics
440
Nuclear Instruments and Methods in Physics Research A244 (1986) 440-443 North-Holland, Amsterdam
A CLOCKED,
FAST ELECTRONICS
Richard GRAY
TRIGGER
FOR HIGH ENERGY
PHYSICS
a n d J o h n P. R U T H E R F O O R D
Physics FM-15, University of Washington, Seattle, WA 98]95, USA Received 18 October 1985
For a Fermilab experiment we have designed and built gated-pulse-stretcher modules which allow us to clock all of the fast electronics with the accelerator rf, thus simplifying the trigger design.
1. Introduction Until recently high energy physics triggers were simple enough that timing could be accomplished module by module with delay cables and redone each time a modification was required. Today, however, triggers have grown in complexity, thus encouraging simplification and standardization of their design. At Fermilab a simplification is possible because of the low frequency (53 MHz) of the accelerator rf cavities: particles arrive in narrow ( - 2 ns fwhm) bunches or buckets separated by 18.8 ns, This separation, longer than at other accelerators, enables formation of a trigger with one bucket resolution. Three additional features of our experiment contribution to the suitability of our approach: (1) all particles accepted by our apparatus are ultrarelativistic so there is no point in time-of-flight measurement; (2) all
scintillation counter (hodoscope) banks are designed so that the maximum time variation of phototube pulses is less than 10 ns, (3) the hodoscope hits are fed to a fast (10 ns) random access memory which is programmed with acceptable patterns [1].
2. Design criteria Clocking of the fast electronics is achieved as follows: Analog signals from 2" phototubes on plastic scintillation counters arrive at LeCroy 4416 discriminators [2] on 200 ns long R G 58 cables. The digital output pulses of these discriminators, set at a width of 15 ns, are fed via ribbon cable to the gated-pulse-stretcher (GPS) (fig. 1). Each GPS module is also fed a - 5 ns wide gate in-time with the accelerator RF. The GPS unit forms the logical A N D of the gate and
One Channel of Gated Pulse
Stretcher
coincidence stretcher i section section Le Croy 4416 discriminator
ED_ 1
~
analog phototube pulse
15
1 I I I
I
I
,-I
r-
-,,q
nsec
L
-I ....
5 ~sec I,
output
I-
1 15 nsec
I 5 nsec
common gate phased to accelerator R.F.
Fig. 1. A block diagram of one channel of the gated pulse stretcher module being fed from a discriminator. Digital pulse widths are indicated. The width of the output pulse (indicated as 15 ns) is set by the timing of the one-shot. 0168-9002/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics (o) signols from some
441
(b) signols from neighboring
R E bucket
R.F bucket
kb8 8~4 R
F PULSE RF. bucket
7r "7 F~----
COUNTER I
earliest s,gnol
COUNTER,,
latest siqnal
7 -] F__U-
•
B
-t---Jlatest signal from buCket A
7
F
e a r l i e s t si~nol from bucket B
COINCIDENCEI.I
7
-'I
]_.i rcoincidence
output
7/-
PULSEourPuTSTRETC.E". COUNTERI
• RF
overlap~
PULSE STRETCHER
OUTPUT.,
COUNTERI I .
EL-
7 ,r- F--
stretched
- l r --F- ,
-l',
r-
I--
R~
CO,NC,OENCE (PS I ) (PS IX)
7
I
nO c o i n c i d e n c e
output
Fig. 2. The relative times of signals from the scintillation counter hodoscopes are indicated here. The case of forming a coincidence between any two such hodoscopes is considered without and with the gated pulse stretcher. Variations in timing due to light transit time in the scintillation counters plus a small amount of jitter due to the phototubes and rf bucket width is less than 10 ns. (a) Variations in timing due to pulses in two hodoscope counters from particles associated with a single rf bucket. Without the gated pulse stretcher, the timing of the coincidence pulse depends primarily on the distance of the particle tracks from the phototubes. With the gated pulse stretcher, the timing is clocked by the accelerator rf. (b) Variations in timing due to pulses in two hodoscope counters where one comes from a particle associated with one rf bucket and the other comes from a particle associated with a neighboring rf bucket. Without the gated pulse stretcher a coincidence pulse may or may not be produced depending primarily on the distance of each particle track from the phototube. With the gated pulse stretcher, no coincidence pulse is produced thus ensuring one-bucket time resolution.
signal pulse a n d then stretches this to a s t a n d a r d w i d t h o u t p u t pulse, the leading edge of w h i c h is clocked to the accelerator rf (see fig. 2).
3. Implementation Sixteen i n d e p e n d e n t G P S c h a n n e l s are c o n t a i n e d in a single w i d t h C A M A C m o d u l e , o b t a i n i n g only p o w e r f r o m the C A M A C d a t a w a y . Fig. 3 is a p h o t o of o n e
Fig. 3. Photograph of the single width CAMAC module containing the 16-channel gated pulse stretcher unit. Table 1 Specifications of the electronics
1) Inputs: Signal: 16, one per channel, in a 2 × 17 connector. Complementary (ECL) levels ( - 0 . 8 V and - 1 . 7 V.) Terminated in 110 ft. Termination resistor packs can be removed to allow bridging of inputs. Gate: One letup front panel connector terminated in 50 12 enables all channels. Latch reset: One lerno front panel connector terminated in 50 $2 resets all channels. 2) Outputs: Signal: Two bridged outputs per channel ECL levels into 110 ~2. Pulse length continuously variable from 12 to 50 ns via screwdriver control common to all channels. Each channel also individually adjustable via internal trimpots. (If only one output used, the other should be terminated.) Outputs are latchable by selecting latch mode via rear panel switch. Latch mode indicated by front panel LED. 3) General specifications: Maximum frequency > 50 MHz Minimum trigger pulse width < 4 ns Transit times - 14 ns Output rise time - 1.5 ns Power requirements (quiescent) - 6 V, 2.25 A Cross talk between channels < 5 mV
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics
442 -SV
-IN +IN
J ~]
12 13
- 5v(
- 5Vq
15
/5 9
/3 4
5 Jr 6
6
_o-r-
- 5V
7
24 GATE.
•
R~T 'I-'-~
-
5V
24
I N4141B
IN4148
47pF
-5V-5V
-5V
-
-
-5V
-SV
-5V- z MR502
4A
-6V
0 pin 38R
Fig. 4. Schematic diagram of the 16-channel gated pulse stretcher unit. One channel is detailed and the neighboring three channels are indicated since they share some chips. The other 12 channels are not shown.
module with the side cover removed. All active components are M E C L 10K. The signal inputs and outputs are c o m p l e m e n t a r y ECL to conform to the LeCroy ECLine S t a n d a r d [3]. The input signals are terminated internally with 110 $2 socketed resistor packs which can be removed to allow cascading of additional units. The comm o n gate input is a N I M signal on a L E M O connector terminated into 50 ~. O u t p u t pulse widths can be changed for all channels simultaneously by a variable resistor, screwdriver-adjustable from the front panel. Each channel also has a trimpotentiometer which can be
accessed with the side removed. O u t p u t pulse widths are adjustable from 12 to 50 ns. W h e n switched to latch mode, each o u t p u t remains set until a reset pulse is received. This mode is not used in the current experiment. A complete schematic is shown in fig. 4 with specifications in table 1. Since 1982 sixteen such G P S units have constituted an integral part of the E605 experiment, a high-rate pair spectrometer where one-bucket time resolution is important.
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics
443
Acknowledgment
References
Help in the specification, design, and construction of this module from D. Forbush, G. Gray, and F. Toevs is gratefully acknowledged.
[1] H.D. Glass, PhD. Thesis, SUNY at Stony Brook (August 1985). [2] LeCroy Research Systems Corporation, 700 South Main St., Spring Valley, NY 10977, USA. [3] ECLine is a trademark of LeCroy Research Systems Corporation.
Nuclear Instruments and Methods in Physics Research A244 (1986) 440-443 North-Holland, Amsterdam
A CLOCKED,
FAST ELECTRONICS
Richard GRAY
TRIGGER
FOR HIGH ENERGY
PHYSICS
a n d J o h n P. R U T H E R F O O R D
Physics FM-15, University of Washington, Seattle, WA 98]95, USA Received 18 October 1985
For a Fermilab experiment we have designed and built gated-pulse-stretcher modules which allow us to clock all of the fast electronics with the accelerator rf, thus simplifying the trigger design.
1. Introduction Until recently high energy physics triggers were simple enough that timing could be accomplished module by module with delay cables and redone each time a modification was required. Today, however, triggers have grown in complexity, thus encouraging simplification and standardization of their design. At Fermilab a simplification is possible because of the low frequency (53 MHz) of the accelerator rf cavities: particles arrive in narrow ( - 2 ns fwhm) bunches or buckets separated by 18.8 ns, This separation, longer than at other accelerators, enables formation of a trigger with one bucket resolution. Three additional features of our experiment contribution to the suitability of our approach: (1) all particles accepted by our apparatus are ultrarelativistic so there is no point in time-of-flight measurement; (2) all
scintillation counter (hodoscope) banks are designed so that the maximum time variation of phototube pulses is less than 10 ns, (3) the hodoscope hits are fed to a fast (10 ns) random access memory which is programmed with acceptable patterns [1].
2. Design criteria Clocking of the fast electronics is achieved as follows: Analog signals from 2" phototubes on plastic scintillation counters arrive at LeCroy 4416 discriminators [2] on 200 ns long R G 58 cables. The digital output pulses of these discriminators, set at a width of 15 ns, are fed via ribbon cable to the gated-pulse-stretcher (GPS) (fig. 1). Each GPS module is also fed a - 5 ns wide gate in-time with the accelerator RF. The GPS unit forms the logical A N D of the gate and
One Channel of Gated Pulse
Stretcher
coincidence stretcher i section section Le Croy 4416 discriminator
ED_ 1
~
analog phototube pulse
15
1 I I I
I
I
,-I
r-
-,,q
nsec
L
-I ....
5 ~sec I,
output
I-
1 15 nsec
I 5 nsec
common gate phased to accelerator R.F.
Fig. 1. A block diagram of one channel of the gated pulse stretcher module being fed from a discriminator. Digital pulse widths are indicated. The width of the output pulse (indicated as 15 ns) is set by the timing of the one-shot. 0168-9002/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics (o) signols from some
441
(b) signols from neighboring
R E bucket
R.F bucket
kb8 8~4 R
F PULSE RF. bucket
7r "7 F~----
COUNTER I
earliest s,gnol
COUNTER,,
latest siqnal
7 -] F__U-
•
B
-t---Jlatest signal from buCket A
7
F
e a r l i e s t si~nol from bucket B
COINCIDENCEI.I
7
-'I
]_.i rcoincidence
output
7/-
PULSEourPuTSTRETC.E". COUNTERI
• RF
overlap~
PULSE STRETCHER
OUTPUT.,
COUNTERI I .
EL-
7 ,r- F--
stretched
- l r --F- ,
-l',
r-
I--
R~
CO,NC,OENCE (PS I ) (PS IX)
7
I
nO c o i n c i d e n c e
output
Fig. 2. The relative times of signals from the scintillation counter hodoscopes are indicated here. The case of forming a coincidence between any two such hodoscopes is considered without and with the gated pulse stretcher. Variations in timing due to light transit time in the scintillation counters plus a small amount of jitter due to the phototubes and rf bucket width is less than 10 ns. (a) Variations in timing due to pulses in two hodoscope counters from particles associated with a single rf bucket. Without the gated pulse stretcher, the timing of the coincidence pulse depends primarily on the distance of the particle tracks from the phototubes. With the gated pulse stretcher, the timing is clocked by the accelerator rf. (b) Variations in timing due to pulses in two hodoscope counters where one comes from a particle associated with one rf bucket and the other comes from a particle associated with a neighboring rf bucket. Without the gated pulse stretcher a coincidence pulse may or may not be produced depending primarily on the distance of each particle track from the phototube. With the gated pulse stretcher, no coincidence pulse is produced thus ensuring one-bucket time resolution.
signal pulse a n d then stretches this to a s t a n d a r d w i d t h o u t p u t pulse, the leading edge of w h i c h is clocked to the accelerator rf (see fig. 2).
3. Implementation Sixteen i n d e p e n d e n t G P S c h a n n e l s are c o n t a i n e d in a single w i d t h C A M A C m o d u l e , o b t a i n i n g only p o w e r f r o m the C A M A C d a t a w a y . Fig. 3 is a p h o t o of o n e
Fig. 3. Photograph of the single width CAMAC module containing the 16-channel gated pulse stretcher unit. Table 1 Specifications of the electronics
1) Inputs: Signal: 16, one per channel, in a 2 × 17 connector. Complementary (ECL) levels ( - 0 . 8 V and - 1 . 7 V.) Terminated in 110 ft. Termination resistor packs can be removed to allow bridging of inputs. Gate: One letup front panel connector terminated in 50 12 enables all channels. Latch reset: One lerno front panel connector terminated in 50 $2 resets all channels. 2) Outputs: Signal: Two bridged outputs per channel ECL levels into 110 ~2. Pulse length continuously variable from 12 to 50 ns via screwdriver control common to all channels. Each channel also individually adjustable via internal trimpots. (If only one output used, the other should be terminated.) Outputs are latchable by selecting latch mode via rear panel switch. Latch mode indicated by front panel LED. 3) General specifications: Maximum frequency > 50 MHz Minimum trigger pulse width < 4 ns Transit times - 14 ns Output rise time - 1.5 ns Power requirements (quiescent) - 6 V, 2.25 A Cross talk between channels < 5 mV
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics
442 -SV
-IN +IN
J ~]
12 13
- 5v(
- 5Vq
15
/5 9
/3 4
5 Jr 6
6
_o-r-
- 5V
7
24 GATE.
•
R~T 'I-'-~
-
5V
24
I N4141B
IN4148
47pF
-5V-5V
-5V
-
-
-5V
-SV
-5V- z MR502
4A
-6V
0 pin 38R
Fig. 4. Schematic diagram of the 16-channel gated pulse stretcher unit. One channel is detailed and the neighboring three channels are indicated since they share some chips. The other 12 channels are not shown.
module with the side cover removed. All active components are M E C L 10K. The signal inputs and outputs are c o m p l e m e n t a r y ECL to conform to the LeCroy ECLine S t a n d a r d [3]. The input signals are terminated internally with 110 $2 socketed resistor packs which can be removed to allow cascading of additional units. The comm o n gate input is a N I M signal on a L E M O connector terminated into 50 ~. O u t p u t pulse widths can be changed for all channels simultaneously by a variable resistor, screwdriver-adjustable from the front panel. Each channel also has a trimpotentiometer which can be
accessed with the side removed. O u t p u t pulse widths are adjustable from 12 to 50 ns. W h e n switched to latch mode, each o u t p u t remains set until a reset pulse is received. This mode is not used in the current experiment. A complete schematic is shown in fig. 4 with specifications in table 1. Since 1982 sixteen such G P S units have constituted an integral part of the E605 experiment, a high-rate pair spectrometer where one-bucket time resolution is important.
R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics
443
Acknowledgment
References
Help in the specification, design, and construction of this module from D. Forbush, G. Gray, and F. Toevs is gratefully acknowledged.
[1] H.D. Glass, PhD. Thesis, SUNY at Stony Brook (August 1985). [2] LeCroy Research Systems Corporation, 700 South Main St., Spring Valley, NY 10977, USA. [3] ECLine is a trademark of LeCroy Research Systems Corporation.