OPA2191 datasheet(20/59 Pages) TI

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7 Parameter Measurement Information

7.1 Input Offset Voltage Drift

The OPAx191 family of operational amplifiers is manufactured using TI’s e-trim operation amplifier technology.

This e-trim operational amplifier 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 7-1 illustrates this concept.

VOS before trim

VOS after trim

Linear component of drift

Temperature

Figure 7-1. 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 7-2 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 operational amplifier 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 7-2 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 7-2, 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.

Temperature (qC)

Offset Voltage vs Temperature

-50

-25

100

125

150

-100

-75

-50

-25

100

Figure 7-2. The Box Method

OPA191, OPA2191, OPA4191

SBOS701D – DECEMBER 2015 – REVISED AUGUST 2021

www.ti.com

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