LMH3401 Datasheet, PDF (35/48 Pages) Texas Instruments – LMH3401 7-GHz, Ultra-Wideband, Fixed-Gain, Fully-Differential Amplifier

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LMH3401
SBOS695A – AUGUST 2014 – REVISED DECEMBER 2014
10.2.2.5 Common-Mode Voltage Correction
The LMH3401 can set the output common-mode voltage to within a typical value of ±30 mV. If greater accuracy
is desired, a simple circuit can improve this accuracy by an order of magnitude. A precision, low-power
operational amplifier is used to sense the error in the output common-mode of the LMH3401 and corrects the
error by adjusting the voltage at the CM pin. In Figure 66, the precision of the op amp replaces the less accurate
precision of the LMH3401 common-mode control circuit while still using the LMH3401 common-mode control
circuit speed. The op amp in this circuit must have better than a 1-mV input-referred offset voltage and low noise.
Otherwise the specifications are not very critical because the LMH3401 is responsible for the entire differential
signal path.
IN±
CM
IN+
±
+
LMH3401
±
+
5 k
5 k
OUT+
OUT-
10 nF
±
LMV771
+
Desired
Vocm
Figure 66. Common-Mode Correction Circuit
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