Tektronix T921 User Manual

Circuit Description-T921/T922/T922R
BLOCK DIAGRAM DESCRIPTION
Most of the circuitry described in this section is common
to
the T921,
T922, and T922R . References to channel 2, dual trace,
chop mode, and vertical switching do not pertain to T921 . The T922R circuitry that differs from the bench version T922 is
described with the three diagrams at the end of this section .
VERTICAL INPUT
Signals to be displayed on the crt are
applied to either the
channel 1 (Y) or channel 2 input connector
. The
input
signals are
amplified by the preamplifier circuits . Each preamplifier circuit
includes separate input coupling, attenuators, gain switching,
variable attenuators, balance, and gain adjustments .
A Trigger Pickoff circuit in each channel
supplies a sample of
the vertical input signal to the Trigger Input Amplifier via the
Trigger Switching circuit and the SOURCE switch .
VERTICAL SWITCHING
The
Vertical Mode switch selects which channel supplies the
trigger signal
.
The vertical signal passes through the Input Buffer
Amplfiier circuit which
isolates the preamplifier circuits from the
Delay Line Driver . In the T922, the output
of each
Input Buffer
Amplifier is connected to the Delay Line Driver through
a Diode
Gate circuit . The Diode Gate circuits are controlled by the
Vertical Switching circuit to select the channel(s) to be displayed .
An output from the Vertical Switching circuit (through the Chop
Blanking Pulse Generator)
is connected to the ZAxis Amplifierto
blank switching transients
in
the chop mode
(SEC/DIV at
1
ms or
slower) . A sync pulse from the sweep (via the Alternate
Sync
Pulse Amplifier) switches the display between channels at the
end of each sweep in the alternate mode (SEC/DIV at
.5
ms or
faster) .
VERTICAL AMPLIFIER
The vertical input signal goes from the Delay Line Driver
through the Delay Line to the Vertical Output Amplifier . The
Delay Line provides approximately 200 ns delay in the vertical
signal
. This
allows the sweep generator circuit time to initiate a
sweep
before the vertical signal reaches the crt vertical deflection
plates . The Vertical Output Amplifier
provides final amplification
of the signal
to drive the crt vertical deflection plates . One section
of the BEAM FINDER
switch,when pressed, causes the display to
compress vertically to aid in locating
off-screen displays . Another
section affects the horizontal circuitry
.
REV . A JUN 1976
TRIGGER
The Trigger
circuit produces a logic triggering signal to trigger
the sweep . Trigger signals are
selected by the SOURCE switch
from three sources : external trigger (via
the External Trigger
Input
Buffer circuit), vertical amplifier input signal (internal), or
the line voltage at
the secondary of T700 . (No trigger signal is
produced during X-Y
operation .)
The selected trigger signal
is amplified and inverted by the
Trigger Input Amplifier . The trigger signal passes
through
coupling capacitor C2132 to the Trigger Level
Comparator, which
determines the voltage level (on the trigger waveform)
at
which
triggering occurs . The SLOPE switch selects the slope or sync
(TV) polarity . The Trigger Level comparatoralso supplies
asignal
to
the TV
Sync Separator circuit .
Two Schmitt Trigger circuits
produce the logic trigger signal ;
one is for conventional trigger signals and the
other is for
TV
signals . The MODE switch selects which Schmitt Trigger circuit
is
operating .
SWEEP AND
HORIZONTAL AMPLIFIER
The
Sweep circuit, when triggered by the Trigger circuit,
produces a linear
sawtooth output signal to the Horizontal
Amplifier . The slope of the sawtooth
is controlled by the SEC/DIV
switch . When the sawtooth output reaches a predetermined level,
the Holdoff circuit resets the Sweep circuit, blanks the
crt
(through the
Z
Axis Amplifier) and prevents subsequent triggers
from initiating another
sweep until the sweep reset is completed .
The sawtooth output from the Sweep circuit is amplified
by the
Horizontal Output Amplifier circuit to produce horizontal
deflec-
tion on
the crt . When the SOURCE switch is in the X-Y position,
the
X
signal, from the External Trigger Input Buffer, is applied
to
the
Horizontal Amplifier . One section of the BEAM FINDER
switch, when
pressed, causes the display to compress horizontal-
ly
to aid in locating off-screen displays .
CRT CIRCUIT
The Z Axis Amplfier determines the crt intensity and blanking
.
TheZ Axis
Amplifier sums the current inputs from several
sources : INTENSITY
control, X-Y intensity limit, unblanking
signal from sweep
circuit, chop blanking signal from the Vertical
Switching circuit and EXTZ AXIS
INPUT connector, J419 .
Output of the Z axis circuit controls the trace intensity
through
the
HV circuit . The HV circuit provides the voltages (greater than
100 V)
necessary for operation of the crt .
The Probe Adjust Generator
provides a square-wave voltage
output for checking voltage probes .
POWER SUPPLY
The Power Supply circuits provide
the low-voltage power
necessary for operation of the instrument .

Tektronix T921 Specifications

General

Brand	Tektronix
Model	T921
Category	Test Equipment
Language	English