Differential nonlinearity

Differential nonlinearity (acronym DNL) is a term describing the deviation between two analog values corresponding to adjacent input digital values. It is an important specification for measuring error in a digital-to-analog converter (DAC); the accuracy of a DAC is mainly determined by this specification. Ideally, any two adjacent digital codes correspond to output analog voltages that are exactly one LSB apart. Differential non-linearity is a measure of the worst case deviation from the ideal 1 LSB step. For example, a DAC with a 1.5 LSB output change for a 1 LSB digital code change exhibits 1⁄2 LSB differential non-linearity. Differential non-linearity may be expressed in fractional bits or as a percentage of full scale. A differential non-linearity greater than 1 LSB may lead to a non-monotonic transfer function in a DAC. ^[1] It is also known as a missing code.

Formula

DNL = Max( | (V_out(i+1) - V_out(i)) - V_{ideal LSB step} | )

See also

• Integral nonlinearity

References

1. ^ INL and DNL definitions "A DNL error specification of less than or equal to 1LSB guarantees a monotonic transfer function with no missing codes. " http://www.maxim-ic.com/app-notes/index.mvp/id/283

External links

• INL/DNL Measurements for High-Speed Analog-to-Digital Converters (ADCs) Application Note 283 by Maxim
• Understanding Data Converters