Tektronix 5441 Instruction Manual page 38

Theory of Operation-5441lR5441
is pressed, -30 V is connected to contact B18 of J620,
turning Q680 on. This increases the voltage level on pin 4 of
U620, allowing the signal from the right-hand vertical plug-in
to pass. If the left-hand vertical plug-in is to be displayed,
the voltage on pin 4 of U620 is decreased by applying
-30 V through contact B18 of J610 to R688. The signal
from the left-hand plug-in now passes through U620. If,
however, both plug-ins have an "on" logic level, the two
logic levels applied to Q680 cancel each other and the signal
from the divider circuit controls the plug-in signal passed. In
the chopped switching mode, the switching between pairs
of amplifiers occurs at a 50 kHz rate (switching occurs on
both the negative- and positive-going transition), and in the
alternate mode, switching occurs at the end of every second
sweep. If neither plug-in has an 'on" logic level, the level at
pin 4 of U620 is such that the left plug-in signal passes to
the vertical amplifier.
The gain of the vertical amplifier portion of U620 is set by
resistors R620 (left plug-in amplifier) and R626 (center plug-
in amplifier). The vertical output signal at pins 12 and 13 of
U620 goes to a grounded-base stage consisting of Q640
and Q660. Q640 and Q660 change the dc level of the verti-
cal signal so that it is compatible with the vertical amplifier in
the display module. Q630 and Q650 act as both a current
source for the grounded base stage and an insertion point
for the vertical readout and trace separation information.
Trace separation information from contact B16 of J630 is
supplied to the emitter of Q650 via (2674. Trace separation
information is only available when a dual time base plug-in is
used.
The vertical Ch switch Off signal is supplied to Q670
where it causes Q674 to be reverse biased during readout
time, thus blocking the trace separation information. The
signal also goes to pin 6 of U620 where it is used to prevent
any vertical signal output from U620 during readout time.
During the time of the vertical Ch switch Off signal, vertical
readout signal information is supplied to the emitter of
Q630.
Horizontal Amplifier
The horizontal amplifier consists of an emitter follower
stage (Q740, (2744) and a gain stage (Q748, Q752). The
gain setting resistor is R750. Thermistor RT754 and resistor
R756 provide a temperature compensation network for the
amplifier.
Trigger Amplifiers
Left Vertical Plug-in. A nominal 250 mvldiv, single-
ended, input signal is applied to the input stage of a two
stage amplifier from contact A4 of J610. The first state, a
paraphase amplifier consisting of Q700-Q708, amplifies the
signal by 114. The second gain stage consists of Q710 and
(2715; R713 sets the stage gain. The output signal ampli-
tude of the trigger amplifier depends upon the input imped-
ance of the time-base trigger circuit at contacts A3 and 84
of J630. Time-base plug-ins designed for 5100-series oscil-
loscopes have a high input impedance, which results in a
signal amplitude of 240 mvldiv. Time-base plug-ins de-
signed for 5400-series oscilloscopes have a low impedance,
which results in a signal amplitude of 50 mvldiv.
Right Vertical Plug-in. The right vertical plug-in trigger
amplifier operates the same as described above.
2-Axis Signal
The gate signal from the A and B sweeps is added on the
interface circuit board. The combined A and B gate signal is
also summed with the trace intensification and chopped
blanking signals before being supplied, via contact 4 of
P755, to the display module as the Z-Axis signal. Diode
CR761 limits the combined signals on the Z-Axis signal line.
C766 and R766, which are in parallel with the input to the Z-
Axis amplifier, serve to increase the rise time of the Z-Axis
signal.
REV MAY 1982