FAST ComTec 2128N Bedienungsanleitung

2128N

Constant Fraction Discriminator

User Manual

Grünwalder Weg 28a, -82041 Oberhaching

Germany

Version 1.2, May 11, 2021

Version 1.0, May 11, 2021

2F ComTec GmbH

Grünwalder Weg 28A . 82041 Oberhaching . Germany

phone: +49 (0 89 665180 0 . fax: +49 (0 89 665180 40 . www.fastcomtec.com

Model 2128N

Constant Fraction Discriminator

2128N 11052021

FEATURES

100 Mh Count Rate

1000 : 1 Dynamic range

Three Operating Modes: CFT, CFRR

constant fraction discriminator with

slow risetime reject, and LET leading

edge trigger

Walk < 30 ps typically for 100 : 1 Range

Simultaneous Dual Positive and

Negative Outputs

Multicolor Count Rate Indicator

DC coupling

DESCRIPTION

The Model 2128N replaces the Model 2128. It is a

fully dc-coupled constant fraction discriminator

with a dynamic range of up to 1000:1. Selectable

fraction and three operating modes provide

optimum time resolution for many detector types

and applications. For example:

CFT – Constant fraction mode for fast detectors

CFRR – Slow rise time reject mode for Ge

detectors

LET – Leading edge mode for single photon

counting

The unit accepts negative polarity pulses to the

50Ω terminated dc-coupled inputs. On customer

request the module can be modified to accept

positive input signals. The constant fraction

composite signal is formed by the sum of a direct,

attenuated (fraction f=0.4 standard signal path

and a delayed, unattenuated path. The delay time

is selectable according to the propagation delay of

a (external 50Ω BNC cable. Careful selection of

fraction and delay cable provides full

compensation of timing distortions due to both

amplitude and risetime variations in the input

signal. Output signals are generated whenever the

input signal exceeds the selected threshold set by

a front panel potentiometer.

Four simultaneous, independent output signals

are provided. The two positive outputs are

adjustable in width, the width then determines the

internal deadtime required to suppress spurious

outputs due to input signal anomalies. The two

negative outputs are fixed-width pulses keyed to

the start of the dead time period.

The front panel ADJUST control and INSPECT

output permit the user to trim the walk

characteristics of the experimental setup for

optimum timing resolution. A frontpanel LED

indicates count rate by color change.

The wide dynamic range of the pent CFT permits

Grünwalder Weg 28A . 82041 Oberhaching . Germany

phone: +49 (0 89 665180 0 . fax: +49 (0 89 665180 40 . www.fastcomtec.com

2128N 11052021

SPECIFICATIONS

Inputs

Input: - accepts -5 mV to about -3.0 V linear

pulses: width > 1ns, Zin = 50 Ohms, dc

coupled; front panel BNC connector.

Delay: two front panel BNC connectors

accept 50 Ohm delay cable in order to form

the internal constant fraction signal.

Outputs

Inspect displays signal of zero crossing

discriminator for use in trimming time walk.

Neg output two independent negative

current outputs, each providing -32 mA into

50Ω, risetime < 3 ns, pulsewidth 5 ns nominal,

dc coupled.

Pos output two independent positive voltage

outputs, providing 2 V (minimum into 50Ω,

risetime < 10 ns, width adjustable by front

panel width trimming potentiometer, which

also determines the internal dead time.

Controls

Threshold Front panel 10-turn locking dial

potentiometer to set acceptance threshold for

input pulses (range ≈ -5 mV to -1 V .

Adjust front panel trimming potentiometer

(screwdriver to compensate walk of the

internal zero crossing discriminator

Leading edge width of the leading edge

signal is internally set by the trimming

potentiometer on the printed board to 20 ns.

CFRR-CFT-LET Frontpanel three-position

switch to select constant fraction with slow rise

time reject (CFRR , basic constant fraction

(CFT , or leading edge timing (LET modes of

operation.

OUTPUT WIDTH Front panel 22-turn

screwdriver adjustable potentiometer to set

width of slow positive output pulse, which is

equal to the internal dead time of the

discriminator – max setting: 1.5 micro sec.

PERFORMANCE

Dynamic range 1000 : 1

CF mode Walk < ±50ps (typically +30ps

for -30mV to -3V range with <2ns rise time.

Count rate up to 100 MHz, limited by dead

time (OUTPUT WIDTH setting

Pulse pair resolution <10 ns, or as limited

by dead time.

Threshold stability better than ±0.02% / 0C

(± 200 ppm / 0C

Threshold linearity ± 0.25 % integral

Temperature range 0 0C to + 50 0C

Delay cable typical lengths (RG-58)

for Plastic, NaI and Si (S.B. detectors 0.5m

to 1m,

for Planar Germanium detectors 1m to 2m

for Coaxial Ge 2.0 to 4m

Typical Power requirements

Standard version

+6.0V 150mA

-6.0V 450 mA

Physical

Si e single width 1/12 NIM module

(3.43 x 22.13 cm; 1.35 x 8.71 inches as per

TID – 20893 (rev.

Net weight 0.7 kg (2.0 lbs

Options

- can be modified to accept positive pulses

- 12V Version available on request

- on request 220 V (ac / 110V (ac

independent from a NIM bin

- Output width for negative output can be

modified

- threshold setting supplied externally via rear

panel connector

- signal shaping using small fractions and RC

shaping by modifying f and capacitors.

This manual contains proprietary information; no part of it may be reproduced by any means without prior

written permission of FAST ComTec, Grünwalder Weg 28a, -82041 Oberhaching, Germany.

Tel: +49 89 665180-0, FAX: +49 89 66518040

mail: [email protected]

The information in this manual describes the hardware and the software as accurately as possible, but is

subject to change without notice.

F ComTec GmbH 3

Table o Contents

1 Introduction.................................................................................................................................................... 6

1.1 General description................................................................................................................................ 6

1.2 Setup information................................................................................................................................... 6

1.2.1 Selection of modes........................................................................................................................ 6

1.2.2 Fraction.......................................................................................................................................... 6

2 Specifications................................................................................................................................................. 7

2.1 Inputs..................................................................................................................................................... 7

2.2 Outputs.................................................................................................................................................. 7

2.3 Controls................................................................................................................................................. 7

2.4 Indicators............................................................................................................................................... 7

2.5 Performance.......................................................................................................................................... 8

2.6 elay cable............................................................................................................................................ 8

2.7 Power requirements............................................................................................................................... 8

2.8 Physical................................................................................................................................................. 8

3 Controls, connectors and indicators............................................................................................................... 9

3.1 Front panel............................................................................................................................................. 9

4 Operation..................................................................................................................................................... 10

4.1 General................................................................................................................................................ 10

4.2 Laboratory bench tests........................................................................................................................ 10

4.2.1 Input............................................................................................................................................. 10

4.2.2 Operating mode........................................................................................................................... 10

4.2.3 elay cable.................................................................................................................................. 11

4.2.4 Walk trim...................................................................................................................................... 11

4.2.5 Outputs........................................................................................................................................ 11

5 Circuit description........................................................................................................................................ 12

5.1 General................................................................................................................................................ 12

5.2 LET mode ........................................................................................................................................... 12

5.3 CFT and CFRR mode.......................................................................................................................... 12

6 Special features and options........................................................................................................................ 13

6.1 Power supply....................................................................................................................................... 13

6.2 Input polarity........................................................................................................................................ 13

6.3 Output width......................................................................................................................................... 13

6.4 Threshold............................................................................................................................................. 13

6.5 Signal shaping..................................................................................................................................... 13

7 iagrams..................................................................................................................................................... 14

7.1 Circuit diagram..................................................................................................................................... 14

7.2 Board................................................................................................................................................... 15

4F ComTec GmbH

Table o Figures

Fig. 3.1: The Front Panel.................................................................................................................................. 9

Fig. 7.1: The Circuit diagram........................................................................................................................... 14

Fig. 7.2: The Board......................................................................................................................................... 15

F ComTec GmbH 5

Introduction

1 Introduction

1.1 General description

The model 2128N is a fully dc-coupled constant fraction discriminator with a dynamic range of up to 1000:1.

Selectable fraction and three operating modes provide optimum time resolution for many detector types and

applications, for example

CFT constant fraction mode for fast detectors

CFRR slow rise time reject mode (e.g. germanium detectors)

LET leading edge mode for single photon counting

(more features are given in section 6)

The model 2128N accepts negative polarity pulses to its 50Ω terminated dc-coupled input. For positive

polarity input pulses see section 6.

The constant fraction composite signal is formed by the sum of a direct, attenuated (fraction f) signal path

and a delayed, unattenuated path. The delay time is selectable according to the propagation delay of a

(external) 50Ω BNC cable. Careful selection of fraction and delay cable provides full compensation of timing

distortions due to both amplitude and rise time variations in the input signal. Output signals are generated

whenever the the input signal exceeds the selected threshold set by a front panel 10 – turn dial

potentiometer.

Four simultaneous, independent output signals are provided. The two positive NIM voltage outputs are

adjustable in width; the width duration sets the internal dead time as required to suppress spurious outputs

due to input signal anomalies. The two independent negative NIM current outputs are derived as fixed width

pulses (see also section 3 and 4).

The wide dynamic range of the model 2128N permits its use in many timing applications without the need of

fast pulse amplifiers.

1.2 Setup in ormation

1.2.1 Selection o modes

Front panel mode switch

CFT constant fraction discriminator

CFRR constant fraction discriminator with slow rise time reject

LET leading edge trigger

1.2.2 Fraction

The factory set fraction is f = 0.4. If a different fraction is required, the resistors R1 and R2

( printed board ) have to be modified as follows:

Z0 = 50

R1 = Z0 · f

R2 = Z0 / f

6F ComTec GmbH

2 Speci ications

2.1 Inputs

Input proceeds -5mV to about -3.0V linear pulses (ref. to the common

mode range of ultra fast comparators),

rise time ≥ 700ps typically,

Zin = 50Ω; dc-coupled front panel BNC connector;

minimum input width ≥ 1 ns,

in the LET mode the CF 2128N accepts shorter input pulses

Delay two BNC connectors for an external delay cable in order to form the

internal constant fraction signal. For specific length see section

4.2.3.

2.2 Outputs

Inspect displays output signal of zero crossing discriminator for use in

trimming the time walk.

Neg. outputs two independent negative current outputs, each providing -32mA

into 50Ω, rise time ≈ 2 ns, pulse width ≤ 5 ns nominal (for longer

pulse width capacitor C4 has to be changed).

Pos. outputs two independent positive voltage outputs, providing 2V into 50Ω,

rise time ≈ 4 ns, width adjustable by front panel trimming

potentiometer, the width then determines the internal dead time.

The maximum width should not exceed 300 ns.

2.3 Controls

Threshold front panel 10-turn locking dial potentiometer to set acceptance

level for input pulses (range ≈ -5 mV to -1V)

Walk adjust front panel trimming potentiometer (screwdriver) to compensate

walk of the internal zero crossing discriminator

CFT-CFRR-LET front panel three position switch to select basic constant fraction

timing (CFT), constant fraction with slow rise time reject (CFRR) or

leading edge timing (LET)

Width front panel trimming potentiometer (screwdriver) to set the width of

the positive output pulse. The width determines the internal dead

time.

2.4 Indicators

Rate LE indicates activity of the discriminator, colour of LE changes by

count rate; yellow-green up to ≈ 5 kHz, orange 5 to about 10 kHz,

red above 10 kHz

F ComTec GmbH 7

Speci ications

2.5 Per ormance

Dynamic range 1000:1 (regarding the linearity of the input pulses)

Walk (CFT mode) in CFT mode for a 1 ns rise time input pulse over a 100:1 dynamic

range (reference – 2.5 V) ≈ 60 ps: typically ± 30 ps

Count rate up to 100 MHz, limited by dead time (width setting)

Pulse pair less than 10 ns, or as limited by dead time

Resolution

Threshold better than ± 0.02% / 0C (± 200 ppm / 0C)

Stability

Threshold ± 25 % integral

Linearity

Temperature 0 0C to + 50 0C

Range

2.6 Delay cable

Typical lengths - for fast pulses ≈ 0,25 m to 1 m

- for pulses from slow detectors (e.g. germanium detectors) 1.5 m

to 4 m

For a better determination of the cable length see also section 4.2.3

for very fast rise times the internal cable lengths have to be taken

into account, see also section 4.2.3.

2.7 Power requirements

+6 V / 150 mA

-6 V / 450 mA (standard version), this power exceeds the normal

BIN power allotment of 167 mA for a single 1/12 width NIM module.

2.8 Physical

Size single width NIM module (3.43 x 22.13 cm;

1.35 x 8.71 inches) per TI – 20893 (rev.)

Net weight 0.7 kg (1.6 lbs)

8F ComTec GmbH

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