Tektronix PG 508 User Manual

12
goes h ig h duri n g t h e p ulse d uration time an d if pin 13 is
low,
p
i n 15 goes h ig h an d p in 14 low . P in 13 controls
U 4000 i n th e square wave
a
n
d exter
n
al d uration mo des .
Duration an d Delay Co n trol
Error
L ig h t Circuitry
Th is circ u itry illu m i n ates t he CO N TRO L ERR
O
R lig h t
w
he
n
t he d uration or delay times a r e greater t han t h e
p erio d
s of t
h
eir respective triggers . T he p ositive pulse
from t he duratio n generator
is fed
i
n to t
h
e D i np ut, p i n 10,
of U 480A . Th e cloc k enable line is
low .
If t he d uration time
is set so t h at α trigger p u lse (connected to t he cloc k i n) for
t h e next duration p ulse occurs before t he output of t h e
d uratio n ge n
erator goes low, t he h ig h on t he D i n put, pi n
10 of U 480A, is transferre
d to t
he
output, p i n 1 .
T h
is
h
ig h is
co nnected to t h e set i n p u t, p i n 5,
of U
480 B wh
ic
h
causes
t h
e outp ut, pi n 2, of U 480 B to go h ig h illuminating the
error lig
h t
.
Wh e
n
t h e out p ut, p in 2, of U 480 B goes h ig h , t he
inputs to U 480A an
d
Β
are disable d t h roug h t h e cloc k
enable li ne p reve n ti ng furt h er trigger in p
uts
until
both fli p
flops are reset . Wh en th e output, pin 2, of U 480 B goes a nd
stays h ig h ,
C487 starts to ch arge to t he voltage on pi n 2,
t hroug h R 490 . T
h is ta k es a pp roximately 100 ms . Wh e n t he
reset i n p u
ts to U 480A an d
Β , p
i ns 13 and 4, reac h th e h ig h
level (about 4 .0 V) U 480A an d Β are
reset a
n
d C487
d isc h arges t hroug h R 490 . Wh en t h ese reset i npu ts retur n
to t he
low
level
both fli p flo ps are rea d y to accept triggers
and t h e error
cycle is rea d
y
to re p eat . If t he d elay time is
set for α time greater t han t h
e period of t he d elay triggers,
t h e h ig h on pi n 7 of U 480 B transfers to p in 2 d irectly, an d
th e lig h t
is illuminate d . R eset ta kes p lace in t he same
m anner as described
above . Also conn ected to t h is
circuitry is α line from t h
e tra n sitio n time board wh ic h also
lig h ts t he CO N TRO L
ERROR lig h t .
"T he CO N TRO L ERR
O
R
lig h t is also illuminate d for
certai n i m pro p er control
setti ngs
.
F ig
.
2-1 sh ows α
simplifie d sc hematic for t h e CO N T R O L ERR
O
R
i n d icator
logic an d co n trol settings causi ng illumi n ation .
V ariable Transition Time Circuitry
T h is circuitry controls t he output tra n sitio n times .
R
esistors
R
534 an d R 536 provide equivale n t 50 Ω termi n a-
tio n im ped a nce for t he
normal (positive-going) i np utfrom
t he duratio n generator . Also, R
520 an dR 522 p rovi d e an
ide n tical termi n ation impe dan
ce for t he com
p
leme n t
i np ut (negative-going) fro m th e du r ation ge n
erator
.
T h
ese i np uts d rive t h e bases of Q525 a n d Q530 . Wh en t he
in p ut from t he du ratio n
generator is h ig h an d t he com p le-
ment is
low,
t he collector
of Q530 d rops from groun d to
abo u t --1/2 V . T h is turns Q565
on an d Q560 off
.
T h e
ad j usta b le co n sta n t current t h ro ugh Q545, to 1-15 V,
is
now passed t h
roug h R 578, from t he -- 15 V supply .
Transistor Q560 is tu rn ed off as its b ase
is connecte d to
groun d . Ze n er d iodes V R620 an dV R630 lowerth evoltage
from t h e b ases of Q565 an d Q560 to t he bases of Q625 an d
Q630 by about 7
.5 V . Tran sisto r Q625 is t h erefore off an d
Q630 is co n ducti ng . Curre n
t flows from --15 V th roug h αη
T h eory
of O p eration---
P
G 508
adj ustable curre n t source Q635 an d t hen
th roug
h
Q630to
c harge t he particular cap acitor d etermine d b y t h e tra n si-
tio n time selected . As t h e cap acitor charges t hrough
α
co n
sta
n
t curren t so u rce, t h e j unction of CR 584 an d
C R 600 goes n egative at
α
li
near rate u n til t he d io de C R 600
turns on . T h is diode serves as t h e n egative clamp . T
h e
voltage at t he anode of C R 600 is set by R 615 t hroug h Q608
and 0600 . T h e voltage at t he ju nction
of C
R
584 a
n
d
C R 600 remains low for t he pulse d uration .
At t he e nd of t he pulse d uration
time, t h e collector of
Q530 goes p ositive . Th is actio n tur ns Q565 off
a nd Q560
on . C ur re
n
t from t h e --i-15 V supply flows t h ro ughconstant
current source 0545,
t
h
e
n
th roug h 0560 raisi n g t he
j un ction of C R 584 a nd CR 600 at α li near rate d etermine d
by
t
h e capacitor val ue an d t he curren t available . T he
j un
ctio
n
of C R 584 and CR 600 goes p ositive u ntil C R 584
turns
on .
T h e voltage at t h
e cat h ode of C
R
584 is set by
R 570 t hroug h Q575 and Q580 . Tran
sisto
r
0625 is tur
n
ed
on , an d Q630 off, p assi ng cu rrent from co n sta n t current
source Q635 t hroug h Q625, C R 604, and R 604 to groun d .
T h
e lea d ing a nd traili ng transitio n times are varie d
indepen d ently
by varying t h e a m ou n t of curre n t passing
t h ro ugh co n sta n t current
source tra n sistors 0635 and
Q545 .
T he
o
u t pu t
waveform at t he j un ction of CR 584 and
CR 600 passes to t he gate
of
fet
Q680 . This fet serves as α
source follower for drivi n g Q685 a nd Q690 . T hese tran-
sistors com
p
ose α linear differe n tial a mp lifier . T he clamp
levels for
d iodes C R 584 an d C R 600 are set so t h at Q685
an d 0690 are slig h tly
overdrive n . T h is serves to r emove
any ri n gi n g or ot h er sig n al irregularities at t h e
to p an d
botto m of t h e waveform . Operatio n al amplifier U 665
p rovi
d es, alo
ng
wit h Q660, consta n t curren t for Q685 and
Q690 .
Transition "rime Control Error L ig h t Circuit r y
Th is circuitry ill u minates
t he co n trol er r or lig h t
w
h e
n
th e lea d ing tra n sition ti m e is greater t han t h
e p ulse
du ration time, or w h en t he traili ng tra n sitio n ti m e is
greater t h
an t h e pulse off time . The i n verted sig n al from
t he leading an
d traili ng ge n erator a pp ears at t he base of
Q704 t h
ro u g
h
fet follower Q700 . Α d iffere n tial amplifier is
formed by Q704 an
d Q706 .
T
he outpu t is ta k en from t he
collector of Q706 . Tran sistors Q704 a n d 0706 are over-
d riven
to reduce t he wi nd ow of comparisio n . Duri n g t he
p ulse on time, t h e base of Q704
is negativewith res p ect v o
grou nd . T h is action causes
t
h
e collector of 0706 to also
go negative, d riving t he base of Q715, an emitter follower
n
egative . T h e emitter of Q715 is co nn ecte d to p i n s 7 an d
10, t he D in p ut
of
fli p flo
p s U 720A and Β .
T he
waveforms drivi n g t he transitio n time circuitry are
also ap plie d
to gates U 740A and Β . P in 6 of U 740 B is h ig h
during pu lse time w h
ile p i n 4 of U 740A is low . Th ep urpose
of t he fo u r gates i n U 740 is
to
d elay t h
e
signal
αρ -
2- 3

Tektronix PG 508 Specifications

General

Brand	Tektronix
Model	PG 508
Category	Pulse Generator
Language	English