HP 5383A

s
M od el
5383 Α
T h eo ry of O pe r atio
n
4-7 . B A L A N C E D I NPU T A MPL I F I ER
4-8 .

( R efe r to F ig ure 4-1 and sc h ematic
.) T h is ci r cu it pr ovi d es a ppr oximately 24 dB m of sig n al
gai n fo r t he Sc h mitt t
r
igge
r i npu t . In a d ditio n , t he bala n ced in pu t amplifie r u ses α fee db ac k
ci r c u it to ensu re t
h
at
t he do level of t he Sc hm itt T r igge r i n p u t r emains co
n
sta
n t i n s p ite
of
i npu t
ci
r
c
u it
o
r tem pe r at ur e va r iatio n s . Dc offsets, t h at r es u lt
f
r om
t h ese va r iatio n s a r e se n se d by
fee db ac k co mp a r ato ι , A1 U 5 a nd co m pa
r
ed
wit h t h e level set by bala nce pote ntiomete r Α 11132 . Α
d iffe r e n ce r es u lts i n compe n sati ng
voltage dr ive to α d iffe r ential te r min al of A1 U 8 . T h is
com pe n sati n g voltage
ultimately dr ives t he o u t pu t of Α 1IJ6 i n α di r ection w h ic h nu
lls
t he o
r
iginal
offset voltage . Fo r example ; if, du e to tempe r at ur e o r ci r cu it va
r iatio n s, t h
e
i npu t d o level to t h e
Sc h mitt T r igge r becomes mo r e p ositive ; A1 U 5 se
n ses t he c h a n ge at its i npu t . The com p a r ato r
r espo nd s b y pr ovi d i ng α negative voltage
w h
ic
h is proportional to t h is p ositive offset . T h is
negative voltage dr
ives
α
d iffe r en tial terminal of A1 U 8 ; fo r ci n g its o u t pu t in α mo
r
e p ositive
d
i r ection . T h is positive inc r ease ca u ses t h e inve r ti ngou t pu t ofA1 U 6togomore negative ;
nu lli ng
t he o r igi n al p ositive offset . T h is co n siste n t d o le v el en s ur es t h at α
si n e wave i n p u t to t he
Sc
h mitt
t r igge r (A1 U 2) pr o du ces α symmet r ical s qu a r e wave ou t pu t .
4-9 . ΤΒΟ ANDMAIN GAT E CI R C U
ITS
4-10 .

( R efe
r
to F
ig
ure
4-1 and sc hematic .) As α r es u lt of t he Sc h mitt t r igge r , signal 'If" is now an
EE C L s qu a
r
e wave t h at is
com p atible to t h e d igital co un te r ci r cu its . Th is s qu a r e wave is a pp lie d to
t h e M ai n
Gate ( p
a r t of Α 1 U1) . Th e M ai n Gate is e n able d by t he low
M
G E
sig n
al
w h
ic
h
is
d
e
r ive d
f r o m t he Τ . Β . (Time B ase) ci r c u its . Thewid t h of M G E , o r "t", is d ete
r
mi
n
ed by t
h
e setti
n g
of t he
f r o n t p anel GAT E TIME switc h . T h e ΤΒΟ coun t d ow n ci r cu its
r
es po
nd
to t
h
e
switc h i npu
t by
co un ti n g d ow n t he 10 MHz ΤΒΟ to pr ovi de α 0 .1, 1 .0, or 10
seco nd M
G
("t") wi d t h ( r efe r to F ig-
ur e 4-5) . It is du ring t h is "t" i n terval, t
h
at t
h
e ena
b le d M ai n Gate p asses sig n al "f" t hr oug h to t he
Deca
d
e Co unte
r
s .
T hese co un te r s co un t t he nu mbe r of cycles (dur i ng i n terval "t") a nd pr ovi de
t he r es u lti n g "η" d ata i n t he fo r m of n ine (4 bit) B CD ch a r acte r s . Th is acc u m u late
d
d ata is
t r ansfe rr ed to
9
sto r age latc h es w he n α T R (t r a n sfe r ) pu lse is r eceive
d
f r om t he Sca n Timing
ci r cu its .
4-11 . SCA N TI M I N G CI R C U ITS
4-12 .

(
R efe
r
to F
ig
ur e
4-1 o r
sc
hematic .) A1 U 24, t h e Sca n Oscillator, is α n omi n al 2 kH z timi n g
sig n al gene r
ato
r . The 2 kH z o u tp u t dr ives t h e Scan Timi ng Ci
r
cu its w h ic h p r ovi de upd ate,
sam p le, a nd d isplay timi ng sig n als to t h e coun te r sto r age latc h es a
nd
t
h
e
d
is p lay
ci r
c
u its . F ig
ur
e
4-2 s h ows t he wavefo r ms associate d wit h t he Sca n Timi ng ci
r
c
u its .
4-13 .

T he upd ate sig n als a r e h el d off un til t h e meas ur 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 ge n e r ation of t h e
followi ng
sig
n
als : R ST
B ( R eset Ti m e
Base),
TR (T r a n sfe r
It
n"
d ata) a nd R SC ( R eset Co un te r s) .

Th ese sig n als a r e sy
n
c
hron
ous
wit h
t
h
e 2 kH
z
Sca
n
Oscillato r . R ST B occur s fi r st a nd r e m ai n s active dur i
ng
t hee
n
ti
r e
up
d ate se qu ence . Typically t h is
se qu e nce lasts a ppr oximately 0 .4
milliseco n ds . 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 seco nd
M
G
i n
te
r val) :
Ο

R
ST
B d isables t h e ΤΒΟ coun t d ow n ci r c u its ( h ol d i ng M G h ig h ) .
T he TR pu lse is ge ne r ate d , t r a n sfe rr i ng all n i ne "η " d ata B CD c
h
a
r
acte
r
s to t
he storage
latc h es . The storage latc h es a
r
e isolate d f
r
om t h e Deca
d
e co
un
te
r s
at
all times, excep t
dur i ng T R pu lse time .
T h e R SC pu lse is ge
n
e
r
ate
d (afte r t h e TR p ulse te r mi n ates) to r eset all coun te r s to ze r o .
4-14 .

Afte r R
SC pu
lse time, t heR ST B sig n al c h a nges state, r eleasi ngthe Τ . Β . countdown ci r cu its
so t hey can initiate anothe r
frequency
meas ur eme n t cycle . F ig ur e 4-3 (on p age 4-6) pr
ovi d
es
wavefo ι ms a nd α d etaile d ci r c u it d esc riptio n of t he d isplay upd ate se qu e
n
ce .