Designers often ask about a typical specification of an amplifier when trying to design a more robust circuit. Due to natural variation in process technology and manufacturing procedures, every specification of an amplifier exhibits some amount of deviation from the ideal value, like the input offset voltage of an amplifier. 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 Electrical Characteristics.

Figure 6-10 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 in Electrical Characteristics are represented in different ways. As a general rule, 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) to more accurately represent the typical value.

Use this chart to calculate approximate probability of a specification in a unit; for example, the typical input voltage offset for the TLV930x- Q1 is 500μV, so 68.2% of all TLV930x-Q1 devices are expected to have an offset from –500μV to +500μV. At 4σ (±2000µV), 99.9937% of the distribution has an offset voltage less than ±2000µV, which means 0.0063% of the population is outside of these limits, which corresponds to about 1 in 15,873 units.

If specifications have a value listed in the minimum or maximum columns, make sure your design specifications are not outside of these ranges.

For specifications with no value listed in the minimum or maximum column, consider selecting a sigma value of sufficient guardband for your application, and design worst-case conditions using this value. For example, the 6σ value corresponds to about 1 in 500 million units, which is an extremely unlikely chance, and can be an option as a wide guardband to design a system around. The TLV930x-Q1 family does not have a maximum or minimum for offset voltage drift in this case, but based on Figure 5-2 and the typical value of 2µV/°C in Electrical Characteristics, calculations show that the 6σ value for offset voltage drift is about 12µV/°C. When designing for worst-case system conditions, this value can be used to estimate the worst possible offset across temperature without having an actual minimum or maximum value.

However, process variation and adjustments over time can shift typical means and standard deviations, therefore only use this information to estimate the performance of a device if no minimum or maximum values are listed.