Input/Output Tables; Non-Digital Services; Cable Distribution; Mode Switch And Calibrator - Tektronix 7140 Instruction Manual

Theory of Operation-7104
INPUT/OUTPUT TABLES
which causes the base and emitter of 0382 to rise
Input/Output (truth) tables show the input combinations
Positive . The positive going voltage is coupled by C376 to
important to a particular function, along with the
the emitter of 0376, turning it off.
resultant output conditions . This table may be given
either for an individual device or for a complete logic
At this time, 0382 is conducting and 0376 is not
stage. Examples of input/output tables for individual
conducting . The voltage at the emitter of 0376 goes
devices can be seen in Table 3-1 .
negative as C376 charges through R376 . When the
emitter-base junction of 0376 becomes forward biased
NON-DIGITAL DEVICES
the oscillator will again change states to complete the
cycle.
Not all of the integrated circuit devices in this instrument
are digital logic devices . The function of non-digital
devices is described
individually, using operating
waveforms
or other techniques to illustrate their
function .
The square-wave signal produced at the collector of
0382 switches 0384 on and off. When 0384 is on, the
current from R383 and R384 flows to ground . When
0384 is off, this current flows through CR386 and R386
into the voltage divider network of R387, R392, R393,
R394, R395, R396, and R397 to produce the 4 volt, 0.4
volt and 40 millivolt Calibrator output voltages . The
accuracy of the Calibrator is set by the 0.4 Volts DC
adjustment, R385 . Both the 4V and 0.4V calibrator
switches must be engaged when adjusting R385 . The
Calibrator frequency is set by the 1 kHz adjustment,
R375 .
Diagram 1, shows the cable inter-connections between
circuit boards within the 7104 .
MODE SWITCHING
0
CABLE DISTRIBUTION
4
MODE SWITCH AND CALIBRATOR
A schematic diagram of the Mode Switch and Calibrator
circuits is given on diagram 2, in section 8 of this manual
(Diagrams and Circuit Board Illustrations) . The schematic
is divided by gray shaded lines separating the circuitry
into major stages . These stages
aid in locating
components mentioned here . Sub-headings use the
stage names to further identify portions of the circuitry
on diagram 2 .
CALIBRATOR
Diagram 3 shows the plug-in interface and the inter-
The Calibrator circuit provides voltage outputs of 40
connections between the plug-in compartments, circuit
millivolts, 0 .4 volt and 4 volts at the CALIBRATOR output
boards, etc. of this instrument . The signal and voltage
connector. A current output of 40 milliamperes is
connections of each interface connector are also
available from the Calibrator circuit with an optional
identified in diagram 3 .
current loop adapter. When using the current loop
adapter the Calibrator must be operated only in the 4 V
switch position, for stated output .
Transistors 0376 and 0382 form a 1 kilohertz, square-
LOGIC
wave oscillator . Oscillation occurs as follows : Initially
assume that 0376 is conducting and 0382 is not
conducting . The voltage at the emitter of 0382 becomes
A schematic diagram of the Logic circuit is given on
more negative as C376 discharges through R381 .
diagram 4, in section 8 of this manual (Diagrams and
Capacitor
C376 discharges until the emitter-base
Circuit Board Illustrations) . The schematic is divided by
junction of 0382 becomes forward biased . As 0382
gray shaded lines separating the circuitry into major
begins conducting the oscillator changes states .
stages . These
stages aid in locating components
Regeneration starts when 0382 conducts and C376
mentioned here . Sub-headings in the following
stops discharging ; this reduces the collector current of
discussion use these stage names to further identify
0376 . Thus, the collector voltage of 0376 rises positive
portions of the circuitry on diagram 4.
The
Mode Switching
circuit includes front-panel
switching and provides the logic for selection of the
vertical and
horizontal compartments to provide
deflection for the crt. The Mode Switching circuit
operates in conjunction with the Logic circuit (diagram 4)
to develop control signals for use in other circuits within
this instrument and plug-in units installed in the plug-in
compartments . Table 3-2 shows the outputs produced
with all combinations of the front-panel switch positions.
4
MAIN INTERFACE