7.3 Feature Description

7.3.1 Phase Reversal Protection

The OPAx992 family has internal phase-reversal protection. Many op amps exhibit a phase reversal when the

input is driven beyond its linear common-mode range. This condition is most often encountered in non-inverting

circuits when the input is driven beyond the specified common-mode voltage range, causing the output to

reverse into the opposite rail. The OPAx992 is a rail-to-rail input op amp; therefore, the common-mode range

can extend up to the rails. Input signals beyond the rails do not cause phase reversal; instead, the output limits

into the appropriate rail. For more information on phase reversal, see Op Amps With Complementary-Pair Input

Stages application note.

7.3.2 Typical Specifications and Distributions

Designers often have questions about a typical specification of an amplifier in order to design a more robust

circuit. Due to natural variation in process technology and manufacturing procedures, every specification of an

amplifier will exhibit some amount of deviation from the ideal value, like an amplifier's input offset voltage. These

deviations often follow Gaussian ("bell curve"), or normal distributions, and circuit designers can leverage this

information to guardband their system, even when there is not a minimum or maximum specification in the

Electrical Characteristics table.

1

1

1

1

1

1

1

1

1

0.00002%

1

1

1

0.00002%

-1

-21

-31

-41

-51

-61

+1

+21

+31

+41

+51

+61

34.13% 13.59%

34.13%

13.59%

2.145%

0.13185%

0.00312%

0.00312%

Figure 7-1. Ideal Gaussian Distribution

Figure 7-1 shows an example distribution, where µ, or mu, is the mean of the distribution, and where σ,

or sigma, is the standard deviation of a system. For a specification that exhibits this kind of distribution,

approximately two-thirds (68.26%) of all units can be expected to have a value within one standard deviation, or

one sigma, of the mean (from µ–σ to µ+σ).

Depending on the specification, values listed in the typical column of the Electrical Characteristics table are

represented in different ways. As a general rule of thumb, if a specification naturally has a nonzero mean

(for example, like gain bandwidth), then the typical value is equal to the mean (µ). However, if a specification

naturally has a mean near zero (like input offset voltage), then the typical value is equal to the mean plus one

standard deviation (µ + σ) in order to most accurately represent the typical value.

You can use this chart to calculate approximate probability of a specification in a unit; for example, for OPAx992,

the typical input voltage offset is 200 µV. So 68.2% of all OPAx992 devices are expected to have an offset from

www.ti.com

OPA992, OPA2992, OPA4992

SBOSA10 – JUNE 2021

Copyright © 2021 Texas Instruments Incorporated

Submit Document Feedback

11

Product Folder Links: OPA992 OPA2992 OPA4992