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BRUEL & KJAER 2209 - Attenuator I and Input Amplifier

BRUEL & KJAER 2209
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Q)
(/)
c:
0
10
0
~-10
Q)
a:
~
-20
·.;;
ro
Qj
-30
a:
-40
-50
-60
-70
~
-
/ h
v
/
~
~
r
/{
fs
I
L
I
I
10
1
2 5
~
v
-
,..
L
A
~
'"
/
,-
5 10
3
2
~~
"
5
Frequency
(Hz)
171~73
Fig.4.10.
A,
8,
C
and
D weighting networks
4.6. ATTENUATOR I
AND
INPUT AMPLIFIER
The
input
attenuator
follows
the
input
stage
and
is
designed
to
step
down
the
input
signal
in
accurate 10 dB steps.
The
range of
the
attenuator
is
0
to
70
dB. A graph of
the
attenuator
frequency
characteristics
is
shown in
Fig.4. 11.
After
the
attenuator
comes
the
input
amplifier. A high
input
impedance
(""'
10
Mil) and a low
output
impedance
(""'
3 Q) ensures negligible loading
of
the
amplifier and
that
loading
by
weighting
networks
or
external
filters
does
not
affect
the
output
signal level.
The
limited
current
handling
capacity
of
the
amplifier requires
that
the
output
is
not
loaded
by
less
than
500
n.
Heavy feedback ensures low
distortion
(<0.1%).
For
calibration
purposes
the
amplification can be varied
from
+ 3
to
-10
dB
by means
of
the
screwdriver
potentiometer
placed
in
the
feedback loop. Fig.5.10 shows
the
frequency
characteristics
of
the
amplifier for various
temperatures.
34

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