photomultiplier amplifier-discriminator
AD8 data sheet
1 description
The AD8 amplifier-discriminator is a compact, low noise, highgain electronics module designed to be used in photomultiplier
photon counting systems to generate TTL output pulses. An
output pulse of fixed width and amplitude is produced for eachphotomultiplier output pulse that exceeds the input discriminator
threshold level. The threshold level is fixed to -2mV, which is
sufficiently sensitive to enable most photomultipliers with 10 ormore dynodes to operate in single photon counting mode.
Two outputs are provided; one with a pulse-pair resolution of25ns for input count rates up to 150Mcps, and the other with apulse-pair resolution of 10µs for rates up to 100kcps. The slower
output is intended to be used where it is required to eliminate
photomultiplier afterpulses.
The AD8 is housed in a metal box and is compatible with theET Enterprises MCS-CT3 multi-channel scaler/counter-timer.
When used together, the AD8 can be powered from theMCS-CT3. These units are also compatible with theET Enterprises range of ambient temperature and cooled
photomultiplier housings, enabling high performance and costeffective photon detection systems to be set up with minimaleffort.

2 applications
counting photomultiplier pulses exceeding a fixed threshold.
single photon counting or applications involving multiple
photodetection pulses.

3 featureshigh input sensitivity and low noise
count rates up to 150Mcps with dead time correction.
signal and power compatible with the MCS-CT3
multi-channel scaler/counter-timer.
input overload protection.
can be used with negative or positive HV photomultiplier
operation.

4 characteristics

unit

min

typ

mV -1000
input pulse amplitude
mV
discriminator level-2Ω
input impedance
50
input protection:
limiting diodes
4.5
V
supply voltage
5
supply current
mA(@ 5V, no signal)
40
supply current
mA(@ 5V, signal = 150Mcps)110Ω
output impedance
50
output pulse
3.3
V
TTL high level (terminated)
pulse-pair resolution:ns
17ns output
25µs
10µs output
10
dead-timens
17ns output
25µs
10µs output
10
output pulse rise and fall time:ns
17ns output
1.2ns
10µs output
1.2
signal rate count(without deadtime correction):cps
17ns output
cps
10µs output
signal count rate(with deadtime correction)cps
17ns outputswarm-up time
1o5C
temperature (operating)oC-40
temperature (storage)%
humidity (non-condensing)gweight
160

max

0

5.5

30M
100k
150M
55
6093

AD8 data sheet
page 2

5 dynamic range

7 external dimensions mm

When using the fast (17ns) output, maximum dynamic range
can be achieved by applying count rate correction tocompensate for the departure from linearity due to pulse pile-up
at high count rates. Dead time may be corrected for, as follows:87

N = n/(1-nT)

TTL OUT
17 ns

Using this correction, deviation from linearity is typically within+/-5% at 120Mcps.

64

INPUT

TTL OUT
10 µs

where: N is the true count rate (cps),
n is the measured count rate (cps),
T is the count rate correction factor (25 x 10-9s),

AD8Amplifier Discriminatoroutput counts (x 106 cps)

100

2610correctedsignal input

uncorrected

1110100

input counts (x 106 cps)

TTL OUT TTL OUT
10 µs
17 ns

6 connections
The TTL output pulses from either the fast (17ns) or slow (10µs)
BNC connectors may be connected to pulse counting equipment
such as the ET Enterprises MCS-CT3 multi-channel
scaler/counter-timer, or other compatible instrumentation. TheAD8 can also be powered from the MCS-CT3, or from theauxiliary low voltage output of the ET Enterprises photomultiplier
power supply HVLAB3000.
Although the AD8 is insensitive to most external sources ofinterference, it is recommended that the connection to thephotomultiplier be made with a 50Ω terminated BNC screened
cable of maximum length 50cm.

signal input
power input
signal output (17ns)
signal output (10µs)

ET Enterprises Limited
45 Riverside Way
Uxbridge UB8 2YF
United Kingdom
tel: +44 (0) 1895 200880
fax: +44 (0) 1895 270873
e-mail: sales@et-enterprises.com
web site: www.et-enterprises.com

50Ω BNC socket
2.1mm dc jack50Ω BNC socket
50Ω BNC socket

ADIT Electron Tubes
300 Crane Street
Sweetwater TX 79556 USA
tel: (325) 235 1418
toll free: (800) 399 4557
fax: (325) 235 2872
e-mail: sales@electrontubes.com
web site: www.electrontubes.com+5V inpower input

8ordering information

AD8boxed electronic module

LEADAD8MCS-CT3

50 cm long power cablewhen used with MCS-CT3

AD8PSU

universal ac power adaptor

LEADBNC - 50cm

50 cm long 50Ω signal cable

LEADBNC - 100cm

100 cm long 50Ω signal cablean ISO 9001 and ISO 14001 registered company
ET Enterprises Ltd 2015
DS_AD8 Issue 2 (30/03/15)