Document type:
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Revision date:
Revision:
User's Manual (MUT)
Mod. N968 Spectroscopy Amplifier
14/06/2004
4
NPO:
Filename:
Number of pages:
Page:
00100/03:N968x.MUTx/04
N968_REV4.DOC
14
13
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a Busy Output, which provides a pulse whose width is equal to the time the input pulse
exceeds the BLR discriminator level and is automatically extended by the generation
of an Inhibit signal.
−
a CRM (Count Rate Meter) Output, which generates a TTL signal every time a valid
input pulse arrives.
3.3 Circuit description
The input signal provided by the preamplifier is processed in the way described in the
Fig. 3.1 block diagram:
Fig. 3.1: N968 circuit block diagram
The amplifying chain is composed by a preamplifier (input stage) and the gain stages. The
coarse, fine and super-fine gain controls operate over these stages, allowing to set the gain
level. The polarity setting is performed through a stage which is configured either inverting
or non-inverting.
The subsequent shaping stage consists of a double 4-pole integrator which forms the pulse
semi-gaussian profile.
The chain composed by both the amplifying and the shaping stages is configured as
“gated-amplifier”, in order to compensate the amplifiers’ thermical drift and offsets, which
would lead to high gain levels saturation and output dynamics reduction.
The fast differentiator stage allows to acquire the pulse’s arrival time through a comparator
(fast discriminator), whose output is used also to form the Count Rate Meter (CRM) output.
Another comparator (slow discriminator) provides the BUSY output, operating directly over
the UNIpolar output.
The baseline restorer (BLR) also operates over the UNIpolar output, and its purpose is to
keep the baseline constantly at the level set through the DC control, in order to decouple
the pulse acquisition from the input rate.
COUNT RATE METER
BASELINE
INHIBIT
BUSY
UNIPOLAR
OUTPUT
BIPOLAR
OUTPUT
POLARITY
INPUT
ATTENUATOR
INPUT
GATED
LOGIC
SLOW
DISC
FAST
DISC
PILE UP
DETECTION
LOGIC
BASE LINE
RESTORER
INPUT
STAGE
GAIN
STAGES
FAST
DIFFERENTIATOR
AUTO
THRESHOLD
SHAPING
STAGE
BIPOLAR
FILTER &
OUTPUT
STAGE
UNIPOLAR
OUTPUT
STAGE &
DELAY
POLE ZERO
VISUAL
INDICATOR
POLE ZERO
ADJUSTMENT
MANUAL
THRESHOLD
LIVE TIME CORRECTION
RISE TIME
PROTECTION