OPA191_0017 Datasheet, PDF (20/51 Pages) Texas Instruments – 36-V, Low Power, Precision, CMOS, Rail-to-Rail Input/Output, Low Offset Voltage, Low Input Bias Current Op Amp

OPA191, OPA2191, OPA4191
SBOS701A – DECEMEBER 2015 – REVISED APRIL 2016
www.ti.com
7 Parameter Measurement Information
7.1 Input Offset Voltage Drift
The OPAx191 family of operational amplifiers is manufactured using TI’s e-trim technology. The e-trim
technology is a TI proprietary method of trimming internal device parameters during either wafer probing or final
testing. Each amplifier input offset voltage and input offset voltage drift is trimmed in production, thereby
minimizing errors associated with input offset voltage and input offset voltage drift. When trimming input offset
voltage drift, the systematic or linear drift error on each device is trimmed to zero. Figure 48 illustrates this
concept.
V_OS Before e-trim
V_OS After e-trim
Linear component of drift
Linear component of drift
Temperature
Figure 48. Input Offset Before and After Drift Trim
A common method of specifying input offset voltage drift is the box method. The box method estimates a
maximum input offset drift by bounding an offset voltage versus temperature curve with a box and using the
corners of this bounding box to determine the drift. The slope of the line connecting the diagonal corners of the
box corresponds to the input offset voltage drift. Figure 49 illustrates the box method concept. The box method
works particularly well when the input offset drift is dominated by the linear component of drift, but because the
OPA191 family uses TI’s e-trim technology to remove the linear component input offset voltage drift, the box
method is not a particularly useful method of accurately performing an error analysis. Shown in Figure 49 are 30
typical units of OPAx191 with the box method superimposed for illustrative purposes. The boundaries of the box
are determined by the specified temperature range along the x-axis and the maximum specified input offset
voltage across that same temperature range along the y-axis. Using the box method predicts an input offset
voltage drift of 0.9 µV/°C. As shown in Figure 49, the slopes of the actual input offset voltage versus temperature
are much less than that predicted by the box method. The box method predicts a pessimistic value for the
maximum input offset voltage drift and is not recommended when performing an error analysis.
Offset Voltage vs Temperature
100
75
50
25
0
-25
-50
-75
-100
-50 -25 0 25 50 75 100 125 150
Temperature (qC)
Figure 49. The Box Method
20
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