LMH6503MAX Datasheet, PDF (19/33 Pages) Texas Instruments – LMH6503 Wideband, Low Power, Linear Variable Gain Amplifier

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LMH6503
SNOSA78E – OCTOBER 2003 – REVISED APRIL 2013
Figure 61. Nulling the Output Offset Voltage
Once this is accomplished, the offset errors introduced by the input stage and multiplier core can then be treated.
The second step requires the absence of an input signal and matched source impedances on the two input pins
in order to cancel the bias current errors. This done, then +1.1V should be applied to V_G and the trim pot located
at R₁₀ adjusted in order to null the offset voltage seen at the LMH6503's output. If a more limited gain range is
anticipated, the above adjustments should be made at these operating points. These steps will minimize the
output offset voltage. However, since the offset term itself varies with the gain setting, the correction is not
perfect and some residual output offset will remain.
GAIN ACCURACY
Defined as the ratio of measured gain (V/V), at a certain V_G, to the best fit line drawn through the typical gain
(V/V) distribution for −1V < V_G < 1V (results expressed in dB) (See Figure 62). The best fit gain (A_V) is given by:
A_V (V/V) = 4.87V_G + 4.61
(7)
For: −1V ≤ V_G ≤ + 1V, R_F = 1kΩ, R_G = 174Ω
(8)
For a V_G range, the value specified in the tables represents the worst case accuracy over the entire range. The
"Typical" value would be the worst case ratio between the "Typical Gain" and the best fit line. The "Max" value
would be the worst case between the max/min gain limit and the best fit line.
GAIN MATCHING
Defined as the limit on gain variation at a certain V_G (expressed in dB) (See Figure 62). Specified as "Max" only
(no "Typical"). For a V_G range, the value specified represents the worst case matching over the entire range. The
"Max" value would be the worst case ratio between the max/min gain limit and the typical gain.
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