Tektronix 455 User Manual

Circuit Description—455/A2/B2
TRIGGER INPUT ^
This circuit determines triggering source and coupling and,
through source follower stages, presents trigger signals to the
Trigger Generator circuit.
SOURCE switches, S2100 (B Trigger), and S2150 (A Trig
ger), select trigger signals from the following sources:
NORM—Signals displayed on the crt.
CH 1—Signals entering Channel 1 vertical input via
emitter follower Q2104.
CH 2—Signals entering Channel 2 vertical input via
emitter follower Q2108.
EXT—Signals entering external trigger input connectors.
EXT -f 10 (A trigger only)—Signals entering A external
trigger input connector attenuated by 10 times
through divider network R2154-C2154 and R2155-
C2155.
LINE (A trigger only)—A sample of the line voltage is
obtained from the power transformer.
STARTS AFTER DELAY (B trigger only)-AI1ows
the B sweep to be gated on by the Delayed Gate pulse
only.
Trigger Coupling
The Trigger COUPLING switches provide a means of accept
ing or rejecting certain components of the trigger signal.
Coupling capacitors C2113 and C2115 (A trigger circuit)
or C2163 and C2165 (B trigger circuit) block the dc com
ponent of the trigger signal, in the AC, LF REJ, and HF
REJ positions. In these positions, frequency components
below about 60 Hz are attenuated.
In the LF REJ position, frequency components of the trig
ger signal below about 50 kHz are attenuated, while in the
HF REJ position, frequency components above about 50
kHz are attenuated. The DC position passes signals from
dc to 50 MHz.
Input Source Follower
Field effect transistors Q2120A and Q2170A are source
followers. They provide high input impedance for the
trigger signals and also provide isolation between the trigger
generator circuit and the trigger signal source. Diodes
CR2123 and CR2173 protect Q2120A and Q2170A
Transistors Q2120B and Q2170B are high-impedance, rela
tively constant, current sources for Q2120A and Q2170A.
They also provide temperature compensation for Q2120A
and Q2170A.
TRIGGER, SWEEP AND
HORIZONTAL PREAMPLIFIER <§> ^
This circuitry contains the Trigger generators. Sweep Gen
erators, Sweep Control, and Horizontal Preamplifier circuits.
Trigger signals, selected by the Trigger Input circuit, start
the sweep. Control of the sweep, in the various modes, is
provided by the Sweep Control 1C (integrated circuit) and
logic circuits contained within the Sweep Generator IC's.
A and B Trigger Generators
The A and B Trigger Generators are contained within two
identical IC's U2600 and U2700. Fig. 4-5 shows a block
diagram of the circuitry in these IC's.
The following is a brief description of the function asso
ciated with each pin of the 1C used for U2600 and U2700.
Pin 1. Ground pin.
Pin 2. Trigger signal in. Input for the trigger signal se
lected by the Trigger Input circuit.
Pin 3. Trigger level in. Connects to the LEVEL control
to determine the level at which the trigger signal at pin 2
produces a sweep-gate output.
Pin 4, 5, 6 and 7. Pins 4 and 7 provide a negative-going
and positive-going sample of the trigger input signal
when power is applied to pins 4, 5, 6 and 7 through the
TRIG VIEW switch in the Vertical Module.
Pin 8. —5 volt supply.
4-12
REV. A, OCT 1975

Tektronix 455 Specifications

General

Brand	Tektronix
Model	455
Category	Test Equipment
Language	English