ORTEC 473 - Leading Edge Operation G; S Output Pulse Generation G; External Selections

5.8. LEADING EDGE OPERATION
Conventional leading edge discrimination can be selected by turning the mode selector switch to L.E. This enables IC8C and
completes the signal path from ULLE to gate G2 in Fig. 5.2 through the delay, DL9. The signal path starts at ULLE, where
the input amplitude triggers a response when it exceeds the adjusted Disc level setting. It is delayed while FF is triggered to
eriab'e G2, and then passes through G2, G3, and G4 to generate a set of three output signals and the deadtime feedback
C "'^•'Ol,
The CF response is not effective because the G1-to-G2 path is not enabled. SRT is set to enable G3 each time a FF response
reaches its input in the L.E. mode, and it is reset from the trailing edge of LLLE. The FF continues to toggle between reset
and set at LLLE and ULLE times, but it enables G2 each time there is a ULLE pulse coming through the delay line.
5.9. OUTPUT PULSE GENERATION
When a decision has been made to generate a set of output pulses, the signal is furnished to pin 5 of IC9B(2). The signal
passes through IC9C(15) to trigger both NIM-standard fast negative output pulse circuits and through 1090(14) to start
Schmitt trigger I010A and IC10B. The Schmitt trigger is the input to the NIM-standard slow positive output generator.
One fast negative output generator uses 012 and 013 as a current switch. The current, at —16 mA, normally flows through
012. When the signal is furnished from 1090(15), 012 is turned off and 013 is turned on to furnish the current through
CN2, assuming the output circuit is terminated properly in 50S2. The other fast negative output generator uses 014 and 015
as an identical current switch that is triggered by the same input signal from 1090(15) to switch the —16 mA from 014 to
015 and through 0N3 to the external circuit.
The Schmitt output at 101 OB(14) is furnished to the positive NIM one-shot circuit that includes 016, 017, and 018. When
the signal is furnished through 063 to 016, the output at CN4 rises from 0 to -1-5 V for a period of about 500 ns.
The Schmitt output at IC10B(14) is also coupled back to pin 4 of IC9B to hold this input high and prevent response to
another signal, if it should come through the circuit, before a controlled dead time has elapsed. 055 is a stretch circuit that
blocks the Schmitt from recovering for a period that is determined by the selection of S1E. When switch SI selects Ge(Li),
Scin, or Ext, the recovery time of the Schmitt circuit is about 50 ns but, for the Nal selection, the recovery time is extended
to about 1 us.
5.10. EXTERNAL SELECTIONS
If the detector selector switch is turned to Ext, three portions of the internal circuits shown in Fig. 5.2 are affected. The
selection of is dependent on the addition of a 50ST delay cable between the Ext Delay connectors on the rear panel, and
the cable length and type determines the amount of external delay.
The selection of the dc fraction is a jumper connection at one of three alternate locations on the printed circuit board. They
a> ' located h tv -en the front corner of the printed circuit board nearest SI and transistor Q2, and are numbered "1", "2",
and "3"
Unless otherwise specified, the wire lead from the 4th position, 2nd wafer, of the detector selector switch is connected to
point "3" for a 30% dc fraction. The wire lead can be moved to point "2" for 20% dc fraction, or to point "1" for a 10% dc
fraction if desired. The value of the dc fraction is always larger than the effective fraction, f, because of the inherent circuit
delays.
an alternate fraction is selected, readjust the constant fraction baseline as follows:
1. Connect a 50f2 terminator on the Input connector.
2. Connect a digital voltmeter from test point TP5 to ground.
3. Adjust the Walk Adj control for —1.25 V at TP5.
Since the basic fraction for 473 operation in Ge(Li), Scint, and Nal modes is 32% (dc), the Walk Adj setting must be changed
again if the detector selector switch is to be used at any of these settings after the Ext adjustment has been made.