6.3 Feature Description

6.3.1 Offset Correction

The input offset voltage of an op amp is a major source of error in many applications. Input offset is caused by

small mismatches in the input transistors and can vary significantly across operating temperature. The mismatch

can be corrected for at the wafer level by measuring the offset voltage and simultaneously adjusting, or trimming,

the current through the input transistors until the offset is near zero.

Each unit of OPAx591 is laser trimmed at production to correct for input offset voltage and input offset voltage

variation across temperature known as offset voltage drift. Offset voltage drift describes the slope of the

input offset versus temperature curve. In devices that exhibit non-linear and non-monotonic input offset over

temperature characteristics, as is common with trimmed field-effect transistor (FET) input amplifiers, special care

must be taken to calculate drift. The the box method, described by Equation 1, is the most common way to

calculate drift.

dVOSdT= VOSMax−VOSMin

TMax−TMin

(1)

Unfortunately, the box method yields a one sided distribution that makes the use statistical analysis

inappropriate. The OPAx591 uses a different method to properly represent drift performance. The OPAx591

is specified by computing the slopes of the input offset voltage versus temperature curve at various points

along the temperature axis. The generated slopes yield normal distributions which are then used to perform

statistical analysis. This method is consistent with other high precision, FET input amplifiers like the OPAx192,

and provides a sufficiently conservative representation of the input offset voltage drift.

A useful curve can be generated to demonstrate how the OPAx591 drift performance varies across different

temperature ranges. Designers can use Figure 6-1 in error analysis for the temperature most applicable to the

application. When performing an error analysis over the full specified temperature range, use the typical and

maximum values for input offset voltage drift as described in Electrical Characteristics.

Temperature ( C)

-40

-25

-10

5

20

35

50

65

80

95

110 125

-1.5

-1.25

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

1.25

1.5

+

−

−4

+4

Figure 6-1. Input Offset Voltage Drift Versus

Temperature

Figure 6-2. Input Offset Voltage Versus

Temperature

The OPAx591 is carefully trimmed to achieve a maximum input offset voltage drift of 1µV/°C. This number

is specified with robust statistical methods on device population bench system measurements. The low drift

enables the amplifiers to be used in very high precision, high voltage applications. The input offset voltage

versus temperature is for the OPA591 is illustrated in Figure 6-2.

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OPA591, OPA2591

SBOSA47A – FEBRUARY 2026 – REVISED SEPTEMBER 2026

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