Tektronix PG 508 User Manual

I n tro d uction
R efer to t he block d iagra m an d t he
sc
h ematics i n t h e
fol d o u t p ages at t he rear of t h is manual as well as t h e
followi n g discussio n to understan d t h e operation of t h e
P
G 508 .
Input Ci r cuitry
T h is circuit r y p r
ocesses
t h
e external
trigger
or gati ng
sig n al p rovi d i ng trigge r i n g waveforms for t he p eriod
circ u it . T h e 50 Ω input impedance for t h is circuitry
is
p rovi de d by R 12, switc h ed in orout by i n ter n al switch S12 .
Wh en R 12 is ou t of t he circuit, t he i n put impeda n ce is
1 Μ Ω , obtained b y R14 a nd R 16 . Dio des C R 16 a nd C R 17
are p rotective
d io des .
T h
e proper voltage at t he d rai n of
020 is set by VR 20 . The source voltage
of
Q20 is set by
VR 22 . Im p edan ce transformation, wit h no voltage sh ift, is
obtai n e d b y sou r ce follower Q20 . Co n sta n t cu rrent for
Q20 is s upp lie d b y Q22 . Α d ifferential comparator is
forme d b y 025 an d
Q26 .
T h
is co
m
parator compa
r
es t he
trigger or gate inpu t level wit h t he level set by t he fro n t
p an el TRIG/GATE control . Consta n t curren t for t h is
comparator is provided by Q30 . L evel co n t r ol voltage fo r
t h e d iffere n tial com p arator is p rovi ded by o p eratio n al
a m p lifier U 40 . T he out p ut, p i n 6, swi ngs over α ra n ge of
±3 V . T hevoltage at ΤΡ
36 is
t h
e triggeri n g level voltage, as
set b y t he TRIG/GATE LE V E L co n trol . If t h e triggering
or
gati n g voltage at t he b ase of Q25 is more p ositive t h at
ΤΡ 36, t hen Q26 is cond u cti n ga nd Q25
is
off . T h
is
places
t h e collector of Q26 more positive t han t h e collector of
Q25 . Wh en t h e gating or triggeri ng waveform level drops
below - ΤΡ 36, Q25 con d ucts an
d Q26
turns off .
T h is switc h i n g waveform
is
applie
d to t he b ases of
U 60A a n d U60 B , op erating as α differential p air . T he
collector of U 60A d rives U 60C i n α casco de mo d e of
o p eratio n . T he collector of U 60C drives t h e base of U 60D
w h
ic h , as an emitter followe r , drives the i np ut of U70 B .
This
gate
operates as αdual i np ut Sc h mitt trigger sha p er .
Wh en t h e emitter of U
60D goes to about 4 .2 V above
g r o und, p i n 7 of U70 B goes h ig h . Wh en t he emitter
of
U 60D d ro ps to about 3 .8 V, p in 7 of U 70 B drops to its low
level . T he i n verti n g out p ut termi n al, p in 6, is always in t he
op p osite state from p
i n 7 . P ositive fee dback for t h is
p ortio n of t he Sc h mitt
is p rovided by
R
72 . If t he unit is
ma n ually triggere d , p i n 10 of U 70 B is momentarily
co
n
necte d to +-5 V . P i n 10 of U 70 B , along wit h R 75 a nd
R
76 now acts as α Sc h mitt s h ape r for t h e ma n ual t r igger .
T h is actio n h ol d s t h e
outp
u
t, p
i
n 7, h ig h and t he i n verti ng
outp ut, p in 6, low as long
as
t h e
MAN button is de p resse d .
REV
.
Α
, ΜΑΥ , 1976
Wh en t he p lus slo
p
e is selected for triggeri ng or gati n g,
f-5 V is a pp lie d to p i n 4 of U 70A . T h is gate is now i nh ibited
an d t he sig n al p asses t hroug h U 70C . As t he outp uts of
U 70A and C are co n nected toget h er, α h ig h on eit h er
outp ut overri des t he low . P in 13 of U 70C is low as lo n g as
t he a n
o
d es
of
C R
82
an d CR 84 are
low,
w h
ic
h occurs w hen
t he logic circuitry h as e n abled t he i n p ut circuitry . Wh en
t he co n trol logic is set to d isable t he i np ut circuitry, t he
anodes of t hese d iodes are raised to +5 V
w h
ic
h
disables
gates U
70Aand
U 70C .
P
in
12
of U 70C now s
h ifts b etween t he h ig h and
low
state corres p o nd i ng wit h t h e input gate or trigger . T h e
ouput from U 70C, p in 14, is p assed to t he perio d circuitry .
Α h ig h at t h e ou tput of U 70C turns t he p eriod circuitry off
and α low starts t he period generator .
T R
IG'D/GAT
E D Lig h t Circuitry
Trigge r ed M ode
Section
2--PG 508
Tra n sistors 0100, Q102, Q110 and t h eir associated
compone n ts com p ose t he circuitry t h at o p erates t he f r ont
p
anel TRIG'D/GAT
E lig h t emitting d io de . T he p air Q100
a
n
d Q102 form α modified
astable
multivibrator, w h ile
Q110 o p erates as α voltage source . Wh en t h e output of
U 70A or U 70C is h ig h (perio d generator off) or t he logic
circ u itry h as in h ibite d t h e i nput circuitry, t h e baseofQ100
is
h ig h .
This causes t he base of Q102 to be low t hr oug h
R 106 . T he collector of 0102 is
now
h ig h a n d t he lig h t
emitti ng d io de is off . Wh en t he b ase of Q100 goes Ιοω , t h e
base of Q102 goes h ig h , t h e collector goes low a n d t h e
lig h t emitting
diode illuminates . T h e lig h t emitting d iode
circuitry follows t he triggeri n g
gate up to
about α5 H z r
ate,
i .e ., about 100 ms on a nd 100 ms off . At faster gati ng
frequen cies, C106 i nh ibits t he c h angi ng states of t h is
circuitry at about t h e 5 Hz rate .
In t he triggere d mo d e of o p eratio n S200-2 is closed .
T h is p laces α h ig h on p i n 10 of U 140 B loc k i ng p i n 7 h ig h
a nd p i n 6 low ir r espective of t he level on p i n 11 . T h is
disa b les t
h
e p eriod ge n erato r . P i n 15 of U 140C now
follows p in 4
of
U 140A in
coi n cide
n
ce wit h
t h
e
in p
ut
triggering signal . P in 14 of U 140C drives Q244 and p i n 15
d rives Q240 . T h e outp ut from t he collector of 0240 is i n
p h ase wit h t h e trigger or gate i nput sig n al p rovidi n g t he
trigger outp u t, an d t he ph
ase of
t he waveform
at
t he
collector of Q244 is i n verted .

Tektronix PG 508 Specifications

General

Brand	Tektronix
Model	PG 508
Category	Pulse Generator
Language	English