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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
the
constant
current source
via
BNC·
socket
SWE
EP I N. The
externaI
voltage
also
controIs the productiveness of the
constant
current
source.
The oscillator also produces a square-wave signa
l
with fixed amplitude which
is
available at
output
socket
SOUARE OUT.
A
triangu
lar
and
square-wave
signal
f
rom the
oscillator
is supplied to
t
he waveform selector
(WAVEFORM).
Depending
of
the
posi
t io
n of the latter
switch
the
du
ty
cycle is
0.
1,
0.5
or
0.9.
In the pos
it
ion
~
of the WAVEFOAM
swi
tch the time-symmetrical triangular wav
eform is
applied to the
SIN
E
SHAP
ER.
The
sinewave formed by the
sine
shaper
is
supplied to the
ATTENUATOR
via
the
waveform
seleetor.
With
controI
AMPLITUD
E
a
co
nt inuous
attenuation
of
the
signal
is
obta
ined.
By
the OUTPUT AMPLIFlER
the signal
is ampl
ifi
ed
to
th
e
required value. In
t
he
o utput
ampl
if ier
the signal can be
set
to
a
seleetable DC·
leve
t
between
O and
10
V with
the
aid
of
switch +
DC
OF
FSET/
O/- DC
OF
FSET and controI DC
OFFSET.
The overrange indicator
OVE
AR ANGE signal
izes,
controlled
by
the
control
s
AMPLITUD
E
and
DC
OFFSET,
tha
t
the
I
imit
of the wo rkabl
e
controi range
of the
o
utpu
t
ampl
ifier
is
overstepped.
With switch O
dB/
-
20
dB
the
output
signa
l
can be
atte
nuated
by 20 dB.
The
ou
t
put
signal
of the generato
r is
ava ilable
at
BNC-soc
ket
OUTPUT.
Switch AU N/HOLD blocks the osci
ll
ato
r
when placed in pos
ition
HOLD.
Then t he
output
vol
tage
stops
o
n
its
last
instantaneous
value.
The
latt
er
function
can
also be
realized by
an
ex
t
ernai d.c.
·volt
age,
applied
to
socket
CONTRO
l
INPUT at
the
rear of
the instrument.
In the SINGL
E
SHOT MOD
E
the
oscill
ato
r is blocked and trigge
red respectivel
y
using single t
riggered
pul ses.
To
o
pe
ra
te this
mode,
con
roi
switch
OFF/
SET
PHASE
/START and
t
o
adjust
the starting
po
int
controi
S
ET
PHASE
have
t
o
be
used
.
The
generator produces a
SINGLE
SHOT
when
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.
The
powe
r
supply
prov
ides
the circu
its,
the
for a
good work ing requi
red stabiliz
d
d.c.·voltages.
3.1.1.
Description
of
the circuit diagram
The function generator
contains the following
units
(see
figs
.
15
and 22)
·
Wave·form
switch
unit
Ul
·
Frequency
-
switch
unit
U2
·
Osci
ll
ator
un
it
U3
· Sine-shape
r
unit U4
·
Contra
l
un it 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-t
ransistor
switching array
2
to generate the
square-wave
voltage
-
a comparator
-
three impedance
transfo
rmers
for
ou
t
put
decoup
i
ing and
-
an amplitude
cont
roi c
ircuit to stabil
ize
the
tr
iangular voltage
at high frequencies.
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