440 Nuclear Instruments and Methods in Physics Research A244 (1986) 440-443 North-Holland, Amsterdam

A C L O C K E D , F A S T E L E C T R O N I C S T R I G G E R F O R H I G H E N E R G Y P H Y S I C S

R i c h a r d G R A Y and 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 sim- ple 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 cavi- ties: 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 resolu- tion. Three additional features of our experiment contri- bution to the suitability of our approach: (1) all par- ticles 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 fol- lows: Analog signals from 2" phototubes on plastic scintillation counters arrive at LeCroy 4416 discrimina- tors [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

Le Croy 4416 discriminator

ED_ 1 r - ~ -,,q

analog 15 nsec phototube

pulse

One Channel of Gated Pulse Stretcher

coincidence stretcher i section section

L -I . . . . 5 ~sec I,

I 5 nsec

common gate phased to accelerator R.F.

1 I I I I o u t p u t

I ,-I I -

1 15 nsec

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 441

R F PULSE

COUNTER I

(o) signols from some (b) signols from neighboring RE bucket R.F bucket

kb8 8~4

RF. • B bucket

7 "7 F~---- - t - - - J - r earliest latest latest signal s,gnol siqnal from buCket A

COUNTER,, 7 -] F__U- 7 F ear l i es t si~nol from bucket B

COINCIDENCEI.II 7 - ' I ] _ . i r -

co inc idence output

P ULSEourPuTSTRETC.E". 7 / - EL- 7 ,r- F-- COUNTER I • RF overlap ~ stretched

PULSE STRETCHER r -

OUTPUT., - l r - F - - , -l' , I-- COUNTER I I . R~

CO, NC,OENCE 7 I (PS I ) (PS IX)

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) Varia- tions 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 and then stretches this to a s t andard width

ou tpu t pulse, the leading edge of which is clocked to the

accelerator rf (see fig. 2).

3. Implementation

Sixteen independen t G P S channels are conta ined in

a single width C A M A C module , ob ta in ing only power

f rom the C A M A C dataway. Fig. 3 is a pho to of one

Fig. 3. Photograph of the single width CAMAC module con- taining 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

442

- IN

+IN

-SV

R. Gray, J.P. Rutherfoord / Fast electronics trigger for high energy physics

J - 5v( 12

~ ] 13 15

6

_o- r- 2 4

GATE. •

2 4 R~T 'I-'-~ - 5 V

- 5 V - 5 V

- 5Vq

/ 5

/3 9

4 5 Jr

7 6

- 5 V

I N4141B I N 4 1 4 8

4 7 p F

- 5 V - - - 5 V - 5 V - z -

- S V 0

M R 5 0 2 4 A - 6 V

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 compo- nents are MECL 10K. The signal inputs and outputs are complementary ECL to conform to the LeCroy ECLine S tandard [3]. The input signals are terminated internally with 110 $2 socketed resistor packs which can be re- moved to allow cascading of addit ional units. The com- mon gate input is a N I M signal on a LEMO connector terminated into 50 ~. Output pulse widths can be changed for all channels s imultaneously by a variable resistor, screwdriver-adjustable from the front panel. Each channel also has a t r impotent iometer which can be

accessed with the side removed. Output pulse widths are adjustable from 12 to 50 ns. When switched to latch mode, each output remains set until a reset pulse is received. This mode is not used in the current experi- ment. A complete schematic is shown in fig. 4 with specifications in table 1.

Since 1982 sixteen such GPS units have const i tuted an integral par t of the E605 experiment, a high-rate pair spectrometer where one-bucket t ime resolution is im- por tant .

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 Corpo- ration.