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Philips PM 5167 - Page 45

Philips PM 5167
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44
3.1.5.1
. --he
emitter-follower
stage
U6/301,
302
acts
as an
impedance
converter.
3.1.5.2
..
'he
cascode
part
U6/303,
305;
304,
306
inverts
and
amplifies
the
voltage.
The
amplification
is
adjusted
with
potentiometer
U6/626,
wh
ile
the
symmetry
is
adjusted
by
means
of
U6/624
.
. -he
total
gain
(no
load
operation)
amounts
to
4.4.
The
bandwidth
then
is
ca.
56
MHz
which
corresponds
to
, rise
time
of
ca.
20
ns (see fig.
9).
- 'he
amplitude
response
and
the
step
function
response
is
optimal
ly
compensated
by
U6/751
and
507
(iee
fig.
9).
3.1.5.3. ' he
driver
stage
consists
of
emitter-followers
U6/307,
308.
3.1 .5.4. i '
he
power
output
stage
operates
in AB
mode
.
The
output
impedance
is
very
low
and
is
terminated
by ca.
~
On
by
means
of
both
series resistors
U6/636,
637.
A
symmetrical
adapted
attenuator
607,
608,
609
is
c
:tive
when
setting
knob
O
dB/-20
dB
to
-20
dB.
3.1.5.5.
l
he
d.c.
offset
voltage
to
be
superimposed
to
the
output
signal
is
fed
to
the
input
of
the
cascode
part
via
r
~sistor
U6/608.
Switch
DC
OFFSET
serves
to
reverse
polarity,
while relevant
potentiometer
DC
OFFSET
€ nables
the
offset
voltage
to
be
adjusted
conti
nuously.
3.1.5.6
.
Ildicator
OVERRANGE
U6/351
and
lamp
821
indicates
overrange
of
the
output
amplifier.
landem
potentiometers
604b,
604a
and
603b,
603a
produce
d.c.
voltages
proportional
to
the
momentary
v
,lues
of
signal ampl
itude
and
DC
OFFSET.
These
d.c. voltages are
added
via
U6/641,
642,
640.
Operational
allplifier
U6/351
compares
the
resulting
voltage
with
the
fixed
reference
voltage
at
U6/643,
644.
As
soon
as
t
le
threshold
value
of
signal
and
DC
OFFSET
30
V,
set
by
potentiometers
AMPLITUDE
and
DC
OFFSET,
is
e<ceeded,
the
comparator
amplifies
the
signal
and
lamp
821
lights.
At
lower
frequencies,
indicator
(iV
E R RANG E I ights
beforehand
and
warns
for
the
expected
overrange
by
operating
potentiometers
,L.MPLlTUDE
or
DC
OFFSET.
3.1.6.
[le
Supply
unit
U7
1 he
DC
supply
unit
fig.
15
contains
two
independent
and
complementary
power
supplies
for a
positive
and
a negative d.c.
voltage
of
30
Veach.
The
output
voltage
of
each
power
supply
is
kept
constant
by
means
of
a voltage
regulation
circuit.
-
3.1.6
.1. 1 he
voltage
regulation
circuit
for
the
positive
supply
voltage
consists
of
:
- an
adjustable
voltage
divider,
U7/608/61
011609
- a
set
point
section,
consisting
of
U7/412,
607
- a
voltage
regulator,
consisting
of
an
amplifier
U7/351
used
as
integrator
- a
regulating
element
consisting
of
a
driver
transistor
U7/301
and
a series
transistor
351
at
the
rear
of
the
i
nstru
ment
.
- a low-pass filter
3.1.6.2.
f!
current
regulating-circuit
takes
over
the
function
of
the
voltage
regulating-circuit. It limits
the
charging
c
ment
to
a
maximum
value
in
case
of
inadmissible
low
load resistances (e.g.
short-circuit).
The
current
fl
gulating
-
circuit
for
the
positive
supply
voltage
consists
of:
- a resistor
U7/603,
which
measu res
the
actual
cu
rrent
- a
stage
U7/302,
which
determines
the
max. load
current
and
at
the
same
time
serves as a
reference
(base-
emitter
voltage)
- a
regulating
element
and
a low-pass filter, identical
to
those
of
the
voltage regulating-circuit.
-
The
regulating
circuits
for
the
negative
supply
voltage are
arranged
accordingly
.
The
supply
voltages are
adjusted
by
means
of
resistors
U7/610
and
U7/630
.

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