Caen 968 Technical document

Technical
Information
Manual
MOD. N968
14 June 2004
Revision n. 4
SPECTROSCOPY
AMPLIFIER
MANUAL REV.4
NPO:
00100/03:N968x.MUTx/04

CAEN will repair or replace any product within the guarantee period if the Guarantor declares that
the product is defective due to workmanship or materials and has not been caused by
mishandling, negligence on behalf of the User, accident or any abnormal conditions or
operations.
CAEN declines all responsibility for damages or injuries
caused by an improper use of the Modules due to
negligence on behalf of the User. It is strongly
recommended to read thoroughly the CAEN User's
Manual before any kind of operation.
CAEN reserves the right to change partially or entirely the contents of this Manual at any time
and without giving any notice.

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TABLE OF CONTENTS
1. GENERAL DESCRIPTION..........................................................................................................................................4
1.1 OVERVIEW...............................................................................................................................................................4
2. TECHNICAL SPECIFICATIONS ...............................................................................................................................5
2.1 PACKAGING.............................................................................................................................................................5
2.2 POWER REQUIREMENTS.......................................................................................................................................5
2.3 FRONT AND BACK PANEL....................................................................................................................................6
2.4 FRONT PANEL CONTROLS....................................................................................................................................7
2.5 INTERNAL JUMPERS..............................................................................................................................................8
2.6 FRONT PANEL DISPLAYS......................................................................................................................................9
2.7 INPUT/OUTPUT CONNECTIONS..........................................................................................................................9
2.8 TECHNICAL SPECIFICATION TABLE.................................................................................................................10
3. FUNCTIONAL DESCRIPTION................................................................................................................................12
3.1 SHAPING DETERMINATION...............................................................................................................................12
3.2 EQUIPMENT FACILITIES.....................................................................................................................................12
3.3 CIRCUIT DESCRIPTION........................................................................................................................................13
LIST OF FIGURES
FIG. 2.1: MOD. N968 FRONT AND BACK PANEL.............................................................................................................6
FIG. 2.2: MOD. N968 SIDE VIEW WITH JUMPERS LOCATION........................................................................................8
FIG. 2.3: UNIPOLAR OUTPUT EQUIVALENT RMS NOISE VS. SHAPING TIME (TS).................................................11
FIG. 2.4: BIPOLAR OUTPUT EQUIVALENT RMS NOISE VS. SHAPING TIME (TS)....................................................11
FIG. 3.1: N968 CIRCUIT BLOCK DIAGRAM......................................................................................................................13
FIG. 3.2: N968 I/O TIMING DIAGRAM..............................................................................................................................14
LIST OF TABLES
TABLE 2.1: POWER REQUIREMENTS................................................................................................................................5
TABLE 2.2: MOD. N968 TECHNICAL FEATURES...........................................................................................................10

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1. General description
1.1 Overview
The Mod. N968 is a spectroscopy amplifier implemented in a single-width NIM module. It
accepts the typical outputs generated from either optical feedback or resistor feedback
preamplifiers connected with nuclear particle detectors.
A front panel switch allows to select between positive and negative input signals.
Gain setting can be performed continuously in the 10 ÷ 1500 range, product of Coarse, Fine
and Superfine Gain. Two internal jumpers allow to set a x0.1 attenuation and a further x2
amplification, thus extending the gain range to 1 ÷ 3000.
Shaping time (Ts) values are 0.5, 1, 2, 3, 6, 10 µs.
The Pole Zero (PZ) cancellation is performed via a front panel screw-trimmer.
The module features also:
-a Bipolar output (to be used for timing purposes)
-An advanced Baseline Restorer (BLR) circuit, with either manual or automatic threshold
setting
-A Pile Up Rejector (PUR) which allows to reject piled up events

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2. Technical specifications
2.1 Packaging
The Model N968 is housed in a single width NIM module.
2.2 Power requirements
Table 2.1: Power requirements
+12 V200mA
-12 V -
+24 V 200 mA
-24 V 200 mA

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2.3 Front and back panel
Fig. 2.1: Mod. N968 Front and back panel
Mod.
N968
FINE GAIN 0.5 - 1.5
COARSEGAIN
SFG
SHAPING TIME
POS
NEG
INPUT
DELAY ON
OFF
DC
UNI BI
PREAMP OUT
INPUT
UNI BI
CRM
BUSY INH
RTP LTC
SPECTROSCOPY
AMPLIFIER
20 1K
50 500
100 200
0.5µs 10µs
1µs 6µs
2µs 3µs
AUTO
THR
PZ ADJ
UN-
COMP
OV-
COMP
B
L
R1
2
3
4
5
6
7
8
9
CL_GND
A_GND
-24V
+12V
+24V
-12V
NC
NC
PRS

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2.4 Front panel controls
FINE GAIN: 10-turn precision potentiometer with graduated dial for continuously
variable direct-reading gain factor of x0.5 to x1.5.
COARSE GAIN: 6-position switch, selects feedback resistors for gain factors of 20, 50,
100, 200, 500, and 1k. Two Jumpers on the printed circuit board select
x0.1 attenuation and x2 Amplification (see § 2.5).
S.F. GAIN: SUPERFINE GAIN, screwdriver adjustable potentiometer to adjust fine
gain; adjustment range: ±2.5 % of the FINE GAIN RANGE.
INPUT: Locking toggle switch, selects either Pos (positive) or Neg (negative)
input pulse polarity.
SHAPING TIME: 6-position switch, selects time constants for active pulse-shaping filter
network from 0.5, 1, 2, 3, 6, and 10 µs.
PZ ADJ1:Screwdriver adjustable potentiometer to set the pole-zero cancellation
to compensate input decay times from 40 µs to infinity.
DELAY: Locking toggle switch, allows to set UNIpolar output either to prompt or
delayed 2 µs.
BLR: 3-position locking toggle switch, selects the source of control for the
gated baseline restorer discriminator threshold from:
−Auto The BLR threshold is automatically set to an optimum level,
as a function of the signal noise, by an internal circuit.
−PZ Adj Enables the PZ adjustment; the BLR threshold is
determined by the Auto function. The BLR time constant is also
greatly increased to facilitate the PZ adjustment.
−Threshold The BLR threshold is manually set by the threshold
potentiometer in the 0 ÷ 300 mV range.
DC: Screwdriver adjustable potentiometer to set the Unipolar Output DC
level; range ±100 mV.
1The adjustment must be performed with a low rate input

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2.5 Internal Jumpers
Some settings can be performed via internal jumpers (location is shown in Fig. 2.2).
Preamp Gain (sw4):allows to set the input preamplifier stage gain either at x1 or
x0.1
PRS Polarity (sw3):allows to configure the module in order to accept on the PRS
input either positive or negative pulses. If the preamplifier
connected to the N968 does not feature the PRS, set the
jumper to positive
G.A. Gain (sw1):allows to introduce either a x2 or x1 gain factor at the Gated
Amplifier stage
Th. Symmetry (sw5):allows to set the BLR negative threshold either symmetric
(equal to the BLR threshold) or asymmetric (BLT threshold +
300mV)
Fig. 2.2: Mod. N968 side view with jumpers location
x1 x0.1
sw4
x2 x1
sw1
ASYMM SYMM
sw5
NEG POS
sw3
PRS POLARITY

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2.6 Front panel displays
PZ VISUAL INDICATOR: PZ Visual Indicator leading to high precision adjustment of the
pole-zero cancellation, for exact compensation of the decay
time of the preamplifier signal. Left LED signals
overcompensation, right LED under compensation. Setting the
BLR switch to the adjust position activates the PZ Visual
Indicator. Under compensation can be corrected by turning the
potentiometer clockwise, while over compensation requires the
potentiometer to be turned anti-clockwise. A correct Pole Zero
setting is signalled by the two LEDs off (or, at least, blinking
low).
2.7 Input/Output connections
INPUTS: INPUT BNC front-and rear-panel connectors, accept either positive or
negative pulses with rise times of 10 to 500 ns and decay times of 40
µs to infinity;
if Preamp Gain = 1, Zin ≅1000 ΩDC-coupled / ≅ 500 Ω AC-coupled;
if Preamp Gain = 0.1, Zin ≅1000 ΩDC-coupled / AC-coupled
linear maximum: 1V (Preamp gain = 1, Amplifier gain = 10), 10 V (x01
attenuation selected); absolute maximum: 10 V.
Front-panel INPUT is provided with a test point.
RTP (Rise Time Protection) Rear-panel BNC connector (TTL signal,
50 Ωimpedance), it is provided by the Multichannel Analyzer (MCA) to
communicate to the amplifier that the ADC lower level threshold is
exceeded and the signal has been accepted. It is used only in the Live
Time Corrector (LTC) circuit.
PRS Reset signal on the Rear-panel D-type 9 pin female connector.
OUTPUTS: UNI Front-panel BNC connector with Z < 0.5 Ω and rear-panel
connector with Z = 93 Ω; short-circuit maximum duration: 10 s (Front-
panel), ?8 (Rear-panel); full-scale linear range of 0 to +10 V; active
filter shaped; DC-restored; DC-level adjustable to ±100 mV.
Front-panel UNI output is provided with a test point.
BI Front-panel BNC connector with Z <1 Ωand rear-panel connector
with Z = 93 Ω; short-circuit maximum duration: 10 s (Front-panel), ?8
(Rear-panel); prompt output with positive lobe leading and linear range
of ±10 V; active filter shaped.
Front-panel BI output is provided with a test point.
CRM Rear-panel BNC connector with Z <10 Ωprovides a nominally +5
V, 100 ns logic pulse every time the input signal exceeds the baseline
restorer fast discriminator threshold.
INH Rear-panel BNC connector with Z <10 Ωprovides a nominally
+5 V logic pulse (suitable for the MCA anticoincidence input) when the
internal pile-up rejection logic detects a distortion of the input signal due

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to pile-up. Signals whose peak occurs when the INH signal is active
must be thus rejected.
BUSY Rear-panel BNC connector with Z <10 Ωprovides a +5 V logic
pulse for the duration that the input pulse exceeds the baseline restorer
discriminator.
LTC Rear-panel BNC connector, provides a positive true TTL logic
signal that is used to stop the MCA time counter; this allows a precise
evaluation of the source actual rate.
PREAMP POWER Rear-panel D-type 9 pin female power connector; it
mates with captive and noncaptive power cords on almost all
preamplifiers. Contact assignment is shown in Fig. 2.1.
2.8 Technical specification table
Table 2.2: Mod. N968 Technical Features
Packaging One unit wide NIM unit
Gain range 1 ÷ 3000
Pulse shape UNIpolar shape: quasi Gaussian, peaking time 2.4 Ts, pulse width at 0.1% level equal to 2.9 times the peaking time
Bipolar shape: approximate derivative, time to crossover 3 Ts
Integral non linearity <± 0.025% @ 2 µs shaping time
Temperature instability
(0 to 50°C)
Gain: < ±50 ppm/°C.
DC level: UNIpolar output: < ±10 µV/°C
BIpolar output: < ±30 µV/°C
Bipolar crossover walk ≤ ±3 ns at 2 µs Ts for 50:1 dynamic range
Overload recovery Recovers to within 2% of rated output from X300 overload in 2.5 nonoverloaded pulse widths using a gain of 1000 for UNIpolar
Output. Same recovery from X1000 overload for BIpolar
Spectrum broadening Typical: <16% FWHM for a 60Co 1.33 MeV gamma line at 85% of full scale for an incoming count rate of 103to 105 counts/s
(Unipolar Output, 2-µs shaping)
Spectrum shift Peak position typical shift: <0.024% for a 60Co 1.33 MeV gamma line at 85% of full scale measured from 103to 105counts/s
(Unipolar Output, 2-µs shaping) (T.B.C.)
Equivalent noise
4 µV / 6 µV (RMS) for UNIpolar/Bipolar output for 3 µs shaping time
and coarse gain = 100
3.5 µV / 5 µV (RMS) for UNIpolar/Bipolar output for 3 µs shaping
time and coarse gain = 1000
[Fig. 2.3: Equivalent RMS Noise Vs. Shaping Time (Ts)]