37
3.
Service
manual
3.1.
DESCRIPTION OF THE BLOCKOlAGRAM (Fig. 6)
The oscillator
is
formed
by
the
CONSTANT
CURRENT
SOURCE, the
CURRENT
INTEGRATOA
and
the
COMPARATOR.
It
produces
and
determines
depending
of
the
posi ion
of
the
frequency
controI
(F REOUENCY
Hz),
the
frequency
range
selector
(F REO. MUL TIPL.)
and
the
frequency
offset
controI
(FAEO
.
OFFSET).
the
frequency
of
the
output
signal.
Switching over from
time
·symmetrical
(duty
cycle 0.5)
to
time'asymmetrica
l
(duty
cycle 0.1
or
0.9) signals
is
achieved by means
of
the
waveform selector (WAV EFORMj, acting
upon
the
constant
current
source.
Sweeping with an externai voltage is
attained
by applying
this
voltage
to th
e
constant
current
source via BNC·
socket
SWEEP I
N.
The externaI voltage also controIs
the
productiveness
of
the
constan
t
current
source.
The oscillator also
produces
a square-wave signal with fixed a
mplitude
which
is
available
at
output
socket
SOUARE
OUT.
A triangular
and
squar
e-wave signal from
the
oscillator
is
supplied
to
the waveform
selector
(WAVEFORM).
Depending
of
the
position
of
the
latt
er swi
tch
the
du
ty
cycle is 0.1,
0.5
or
0.9.
In
the
position ~
of
the
WAVEFOAM swi
tch
the
time-symmetrical triangular wave
form
is
applied
to
the
SINE SHAPE
R.
The sinewave
formed
by
the
sine
shaper
is
supplied
to
the
ATTENUATOR
via
the
waveform
seleetor.
With
controI
AMPLITUDE a co
nt
i
nuou
s
attenuat
ion of
the
signal is
obta
ined. By
the
OUTPUT AMPLIFlER
the
signal is ampl i
fi
ed
to
th
e required
va
lue. In the ou
tput
amp
l ifier
the
signal can be set
to
a seleetable DC·
le
ve
t
between
O
and
10
V
with
the aid
of
switch +
DC
OF
FSET
/
O/-
DC OF
FSET
and controI
DC
OFFSET.
The
overrange indic
at
or
OVE
AR
ANGE sign
al
izes,
controlled
by
the
control
s AMPLITUDE and
DC
OFFSET
,
tha
t
th
e Iimit
of
the
wo
rkable
contr
oi range
of
the
o
utpu
t amplifier is overstepped.
With switch O dB/-
20
dB
the
outpu
t signal
can
be a
tt
e
nuated
by
20
dB.
The
out
put
signal
of
the
g
ene
r
ato
r
is
available at BNC-sock
et
OUTPUT.
Sw
i
tch
AU
N/HOLD blocks
the
osci
ll
ato
r when placed in position HOLD.
Then
the o
utpu
t vol tage stops on i
ts
last
instantaneou
s value.
The
l
att
er
function
can also be realized by an
externai d.c.·voltage,
app
l
ie
d
to
socket
CONTRO
l INPUT
at
the
rear
of
the
instrument.
In
the
SINGL
E
SHOT
MODE
th
e oscillator is bl
ocked
and triggered respectively using single t riggered pulses.
To
ope
ra
te
this
mode
, con roi switch
OFF
/
SET
PHASE/
START
and
to
adjust
the
starting point
controi
SET
PHASE have to be used.
The
generator
produces
a SINGLE SHOT wh
en
pushing
the
controi
switch
to
position
START
or
by applying
a negative pulse
to
the
CONTROl
INPUT.
The
HOlD
·fu
nction
can also be used in
the
mod
e
SI
NG
LE
SHOT.
Th
e
pow
er supply prov ides
the
circuits,
the
for a good
work
ing requir
ed
stabiliz d
d.c
.·voltages.
3.1.1.
Description
of
the
circuit
diagram
The
f
unction
generator
contains
the following
unit
s
(s
ee figs. 15
and
22)
· Wave·form switch unit
Ul
·
Frequency
-
sw
itch
unit
U2
· Osci
ll
ator
unit U3
· Sine-shaper
unit
U4
·
Contra
l unit U5
· Power ampl ifier
unit
U6
· d.c
.-
supply
unit
U7
3.1.2. Oscillator
unit
U3
The
oscilla~or
,
see figs. 7
and
22, mainly consists of:
- a four·
transistor
switching array 1
to
generate
the
triangular voltage
- a four-transistor switching array 2
to
generate
the
square-wave voltage
- a
comparator
-
three
impedance
transfo
rmers
for
ou
t
put
decoup
i i
ng
and
- an
amplitude
con
troi circuit
to
stabilize
the
tr
iangular voltage at high frequencies.
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