Service manual

2
2. SPECIFICATIONS
2.1. PERFORMANCE
INPUT
Accepts negative input signals from 0 V to
-5 V without saturation; dc-coupled; Z
=
50 ;
in
reflections +5% for t 2 ns.
r
THRESHOLD RANGE
-5 mV to -1 V.
THRESHOLD INTEGRAL NONLINEARITY
±0.25% of full scale.
THRESHOLD INSTABILITY
±100 µV/ C to
50 C.
PROPAGATION DELAY
Nominally 25 ns, with
external CF Delay 2 ns.
MINIMUM PULSE-PAIR RESOLUTION
20 ns.
DEADTIME
Nominally 20 ns or blocking output
width, whichever is greater.
BLOCKING OUTPUT WIDTH
Adjustable from
10 ns to 1000 ns.
TIME WALK
±100 ps for the 100:1 input range
from -20 mV to -2 V; ±150 ps for the 200:1 input
range from -10 mV to -2 V. Conditions: external CF
Delay 2 ns; input rise time 1 ns; input pulse
width 10 ns.
2.2. CONTROLS
THRESHOLD
Front panel 10-turn precision
locking potentiometer determines the discriminator
threshold setting in the range from -5 mV to -1 V.
TIMING MODE SWITCH
Front panel 3-position
locking toggle switch selects one of the three timing
modes:
CF (Constant Fraction)
Attenuation factor is
internally set at f = 0.2 (can be changed upon
request). An external 50 coaxial cable must be
provided for the constant- fraction shaping delay
(CF Delay).
SRT(Slow Rise Time Reject)
Provides constant -
fraction timing and inhibits output signals that would
be produced by leading-edge timing from the
leading-edge arming discriminator. An input signal
that does not cross the discriminator threshold
before the constant-fraction zero-crossing time does
not produce an output pulse.
LE (Leading Edge)
Inhibits timing from the
constant- fraction circuitry. The timing is derived as
the leading edge of the input signal crosses the
discriminator threshold level.
CF DELAY
Two front panel BNC connectors
accept 50 coaxial cable to set the required
constant-fraction shaping delay for the CF and SRT
Modes: total delay is 0.8 ns plus the delay of the
external cable. In the LE Mode, the user may either
connect a piece of 50 coaxial cable between
these two connectors or connect a 50 termination
to each of the two connectors.
WALK
Front panel 20-turn screwdriver adjustment
sets the walk compensation for each application.
CF MON
Front panel BNC connector permits
observation of the constant-fraction bipolar timing
signal; Z = 50 . 50 coaxial cable required; 50
o
termination suggested.
WIDTH
Front panel 20-turn screwdriver adjustment
sets the width of the blocking output pulse. Variable
from 10ns to 1000ns. Sets the instrument
deadtime for widths nominally >20 ns.
GATING MODE SWITCH
Rear panel 2-position
locking toggle switch controls the use of the Gate
Inputs. (One of three Gate Input signal paths is
selected by a printed wiring board, PWB, jumper.)
Gated
A "true" logic level from the selected Gate
Input permits output signals to be generated by the
discriminator. A "false" logic level from the
selected Gate Input inhibits output signals from
being generated by the discriminator. A set of
output signals already in progress is not terminated
prematurely by a logic "false" signal from the
selected Gate Input.
Ungated
The signal level of the selected Gate
input does not inhibit normal generation of output
signals from the discriminator (i.e., the discriminator
is always enabled).
LOGIC CURRENT SWITCH
Rear panel 2-position
locking toggle switch selects either the -6 V or the
-12 V NIM supply line for providing current for the
high-speed ECL logic used in the discriminator.