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2-14
2.3.
CIRCUIT DESCRIPTION
2.3.1.
Main Time-base Triggering (see Fig.
Trigger selection circuit and trigger input stage (A, B, COMP)
a)
The trigger signal from the vertical channel A
symmetrical current signal. The output is a symmetrical voltage signal that is routed to the series feedback stage
Channel A is selected as MTB trigger source if R918 in the emitter circuit of V873, V876 is connected to earth
via the MTB trigger source selector switch
The trigger signal from vertical channel B is applied to shunt feedback amplifier V914, V916, which i s followed
by a series feedback stage V878, V879, for MTB triggering and a series feedback stage V877, V881 for DTB
triggering. These amplifier stages are identical to those described above for channel A.
The composite trigger signal obtained from V833 and V834 in the delay line driver is applied to shunt feedback
amplifier V917, V918.
This amplifier i s followed by a series feedback stage, V882, V883 for MTB triggering. If R892 in the emitter
circuit of V882, V883 is connected to earth via the MTB trigger source switch S23 via switching transistor
If in composite trigger mode TRIG VIEW is selected, a logic H level from D634-10 makes V880 conductive via
conductive and an earth potential i s applied to R918 via V860 to select channel A as MTB trigger source.
As a result, it i s not possible to switch on the trigger view and composite trigger modes together.
External and line trigger input
The external trigger signal can be applied to input socket X5. The signal i s routed via a network that gives the
correct external input impedance and sensitivity, and via C1109 (a.c.-component), R1122, R1123 (d.c.compo-
nent) to the gate of FET V1104. In the LF and HF trigger coupling modes the d.c. component of the signal is
interrupted because the junction of R1122, R1123 is connected to earth via LF and HF switches S20.
FET V1104 i s part of the balanced source-follower stage. One FET receives the external trigger signal and the
other, the LINE trigger signal. The trigger source signal not desired i s short-circuited to earth.
The LINE trigger signal, originated in the power supply, i s routed via the potentiometer R891 (LINE) to the
TRIGGER SELECTION UNIT.
The amplifier stage V1104 is followed
input voltage signal into a symmetrical output current signal.
Transistor V1101 provides a common current-source in the emitter circuit, which i s only switched in if EXT or
LINE triggering is selected (an earth potential from trigger source selector switch S23).
For instruments with TTL trigger facilities (optional), the gain of the amplifier stage V1102, V1103 can be
increased by a factor of 2.5 (relay contact K1101 closes in the TTL trigger mode).
Trigger amplifier input stage
This amplifier has two balanced inputs that apply an input signal to the common-base circuit V852, V853.
The input current is routed via socket X859 and socket X863 for MTB triggering via channel A, B or composite.
The input current signal isrouted via sockets X861 and X862 for MTB triggering via the EXT input or LINE.
The common-base circuit V852, V853 i s followed by a shunt feedback stage V851, V854 that converts the
input current signal into an output voltage signal. This output signal is taken off asymmetrically and applied to
the DC, LF, HF filter.
OF
THE HORIZONTAL SECTION
8.5.)
is
applied to shunt feedback amplifier V912, V913, as a
S23, to switch on these transistors.
by
a series feedback stage
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