Datasheet
OUTPUT VOLTAGE DYNAMIC RANGE OFFSET ADJUSTMENT
BANDWIDTH
+V
IN
R
G+
R
G-
-V
IN
FB
R
G
50W
10kW
1kW
50W
V
IN
VCA824
R
F
0.1 Fm
0.1 Fm
10kW
4kW
+5V
-5V
V
OUT
+5V
-5V
InputStageandMultiplexerCore
OffsetCompensationCircuit
OutputStageOffset
CompensationCircuit
VCA824
SBOS394C – NOVEMBER 2007 – REVISED DECEMBER 2008 .......................................................................................................................................
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With its large output current capability and its wide As a result of the internal architecture used on the
output voltage swing of ± 3.9V typical on 100 Ω load, it VCA824, the output offset voltage originates from the
is easy to forget other types of limitations that the output stage and from the input stage and multiplier
VCA824 can encounter. For these limitations, careful core. Figure 88 shows how to compensate both
analysis must be done to avoid input stage limitation: sources of the output offset voltage. Use this
either voltage or I
RG
current. Note that if control pin procedure to compensate the output offset voltage:
V
G
varies, the gain limitation may affect other aspects starting with the output stage compensation, set
of the circuit. V
G
= – 1V to eliminate all offset contribution of the
input stage and multiplier core. Adjust the output
stage offset compensation potentiometer. Finally, set
V
G
= +1V to the maximum gain and adjust the input
The output stage of the VCA824 is a wideband
stage and multiplier core potentiometer. This
current-feedback amplifier. As such, the feedback
procedure effectively eliminates all offset contribution
resistance is the compensation of the last stage.
at the maximum gain. Because adjusting the gain
Reducing the feedback element and maintaining the
modifies the contribution of the input stage and the
gain constant limits the useful range of I
RG
, and
multiplier core, some residual output offset voltage
therefore, reduces the gain adjust range. For a given
remains.
gain, reducing the gain element limits the maximum
achievable output voltage swing.
Figure 88. Adjusting the Input and Output Voltage Sources
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