Datron 1061 Calibration And Servicing Handbook page 32

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24
3.2.3.4 Hish
Speed Buffer
C22 slows
the switching
edges
from the multiplexer
M35 so
that the buffer cannot slew-limit
and
thus lose
the
charge. The signals are fed
to
036,
M34 which comprise a
high
speed
buffer
with
high
common mode rejection
ratio (See
Fig. 3.16). The
common mode rejection
is
dependent
on the power
supplies
of 036
(from
R66 and
R11-R15)
being
bootstrapped
to
the
output of the buffer,
via D2 and D4. Thus the difference
between
input
signal
and power supply around
the input
stage
is
maintained
constani whatever
the input
signal.
3.2.3.5 lntegrator
The
basic
lntegrator
comprises
R6,
R7 and C9,
with
hybrid amplifier O35
and
M25. (See Fig.
3.17).
Low-noise
FÊT-pair
O35 also has
low
gate
leakage,
which
maintains
the
effectiveness
of
'sample-and-hold'
components R34
and C12.
An
inverted and attenuated version
of the integrator
output
voltage
is
developed across
R5'
This is
applied via
R4 and C10
to
compensate
for
the
small
amount of
dielectric absorption
in
C9. The value
of
R5 is factory'
selected
to
equalize readings
of
the
same
input, taken
at
differing read-rates
(including'one'shot'
measurements)'
Cl1
and R27 provide shorter
term
compensation,
R23 being set
to
correct
linearity at
10%
of
full
range'
R12l
R11
M34
+
R35
R66
036
R36
Fig.
3.16
HIGH SPEED
BUFFER CIRCUITRY
D4
c18
o3
R15/R14
c22
R8
o1
o4
+
c19
+
D2
R10
TP5
-15V
To
lntegrator
From
Multiplexer
M35
rl/¡22
+
R25
M25
o35
R31 R33
R26
R23
cl2
R32
R6/R7
R59
R28
c9
+
R34
From
-1
R4
c10
c11
R27
Fig.
3.17
INTEGRATOR
ClRCUlr
To
znd Null
Detector
R5
FSV
.. ..1.
'
Hi,-,1i,'
ti,-,,,,,
:
i,'**;r"-i''1
'.,'..
-
.
,,
"
,'t ,-tlri :.-.
:'
.i'.i
.'-,