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s
M
o del 5383Α
T
heory of O p e ratio n
4-7 .
B
A LA N C ED I NPU T AMPL I F I ER
4-8 .
( R efe r to
F
igure 4-1 and sc h ematic .) T h is ci rcu it provi d es a pproximately 24 dBm of sig n al
gai n fo r
t
h e Sc h mitt t r igge r
i
n pu t . In a dditio n , th e balan ce d in pu t amplifier u ses α feedbac k
cir c u it to ens u re t h at th e
d
o level of the Schmitt T r igge r
i
n pu t
r
emains co n sta n t i n
s
pite of input
ci r c u it o r tem pe rat ure var iations . Dc offsets, th at
r
es u lt f rom th ese va r iatio n s ar e se n sed by
feedb ac k compa rato ι , A1 U 5 a nd com pa r e d wit h th e level set by bala n ce potentiomete r Α 11132 . Α
d
iffere n ce
r
es u lts i n compe nsati ng voltage drive to α
d
iffe rential te r mi nal of A1 U 8 . Th is
com p e n sati n g voltage ultimately dr ives t he o ut put of Α 1IJ6 i n α di rection w h ich nu lls th e o r iginal
offset voltage .
F
o r example; if, due to temperature or ci rcu it va riatio n s, t h e i npu t
d
o level to t h e
Sc h mitt T rigge r becomes mor e
p
ositive ; A1 U5 se n ses t h e c h a n ge at its i npu t. T h e com p ar ato r
r espo nd s
b
y provi d i ng α negative voltage w h ic h is proportional to t h is
p
ositive offset . Th is
negative voltage dr ives α
d
iffe re n tial terminal of A1 U 8 ; fo r ci ng its ou t pu t in α mo r e
p
ositive
d
i rection . T h is positive inc rease ca uses t h e inve rtin g o u tpu t ofA1 U 6togomore negative ; n ulli n g
th e o rigi n al
p
ositive offset . Th is co nsistent
d
o le vel en s ures t h at α si n e wave i n p u t to t h e Sc h mitt
trigge r (A1 U 2) produ ces α symmetrical s qua re wave o u tpu t .
4-9 . ΤΒΟ AN D MAIN GATE CIRCU ITS
4-10 .
( R efe r to
F
ig ure 4-1 and sch ematic .) As α
r
es u lt of the Sc hmitt t rigge r , signal 'If" is now an
EE C L
s
qu a r e wave th at is com p atible to t h e
d
igital co un te r ci r cu its . T h is squ a re wave is a pp lied to
t h e
M
ai n Gate ( p a rt of Α 1
U1) .
Th e
M
ain Gate is en abled by t h e low
M
GE sig n al w h ic h is
d
e rived
f
ro m
t
h e Τ .Β . (Time B ase) ci rc u its . Th e wi dth of
M
GE
,
o r "t", is
d
ete r mi n e d by t h e setti n g of t h e
f ro n t
p
anel GAT E TIME switch . T he ΤΒΟ coun t
d
ow n ci rcu its
r
espo nd to t h e switc h
i
npu t by
co un ti n g
d
ow n
t
h e 10 MHz ΤΒΟ to provi de α 0 .1, 1 .0, or 10 seco n d
M
G ("t") wid th (refe r to
F
ig-
ur e 4-5) . It is
d
u ring t h is "t" i n terval, t h at t h e ena ble d M ain Gate
p
asses sig n al "f" t hroug h to t h e
Deca d e Co u nte r s . Th ese co un ters co un t th e nu mbe r of cycles (dur i n g i n terval "t") and pr ovi d e
th e
r
esu lti n g " η "
d
ata i n
t
he for m of
n
ine (4 bit) B CD ch a r acte rs . Th is acc u m u late d data is
t ransfe rred to 9 sto rage latch es w he n α
T
R (t ra nsfer ) p ulse is
r
eceive d
f
r om t h e Sca n Timing
circu its .
4-11 . SCA N TI M IN G CI RC UITS
4-12 .
( R efe r to
F
ig ure 4-1 or sc hematic .) A1 U 24, t he Sca n Oscillator, is α
n
omi n al 2 kH z timi n g
sig n al ge n e r ato r. T h e 2 kHz outpu t dr ives t h e Scan Timi n g Ci r cu its w h ic h
p
rovi d e upd ate,
sam p le, a nd d isplay timi ng sig n als to t he counte r sto rage latc h es a nd
t
h e
d
is p lay ci r c u its .
F
ig ur e
4-2 sh ows th e wavefo rms associated with
t
h e Sca n Timi ng ci r c uits .
4-13 .
Th e upd ate sig nals a r e
h
el d off until t he measur i n g time i n terval, "t", e nd s . At t h is time
M
G goes
h
ig h enabli n g gen e ration of t he followi ng sig n als: RST B ( R eset Ti m e Base), TR (T ra nsfe r
It
n"
d
ata) a nd R SC (Reset Co un ter s) .
Th ese sig nals are sy n c hro n ous with
t
h e 2 kH z Sca n
Oscillato r. R STB occ urs fi rst and r e m ai ns active dur i ng th e e n ti re up
d
ate sequ en ce . Typically t h is
sequ en ce lasts approximately 0 .4 milliseco nds . During t h is b r ief time (i .e ., b r ief i n proportion to
t h e 0 .1, 1 .0, o r 10 second M G i n te rval):
Ο R ST B d isables t h e ΤΒΟ coun t
d
own ci r cu its ( h old i ng
M
G
h
ig h) .
Th e TR pulse is ge ner ated , t ra nsferr i ng all
n
i n e "η "
d
ata BCD c h a r acte r s to t h e storage
latch es . T he storage latc hes a r e isolate d
f
r om t he Deca d e co un te rs at all times, exce p t
dur i n g
T
R pu lse time .
T he R SC
p
u lse is ge n e r ate d (after
t
h e T R pulse te rmi n ates) to
r
eset all co un ters to zero .
4-14 .
Afte r R SC pu lse time, th e RSTB sig n al c ha nges state,
r
eleasin g theΤ . Β . countdown ci rcu its
so th ey can initiate anothe r frequency meas ureme nt cycle.
F
igure 4-3 (on
p
age 4-6) pr ovi d es
wavefo ι ms a nd α
d
etaile d ci rc u it
d
escriptio n of th e
d
isplay upd ate sequ e n ce.
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