THS1007

SLAS286B − AUGUST 2000− REVISED DECEMBER 2010

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DEFINITIONS OF SPECIFICATIONS AND TERMINOLOGY

Integral Nonlinearity

Integral nonlinearity refers to the deviation of each individual code from a line drawn from zero through full scale.

The point used as zero occurs 1/2 LSB before the first code transition. The full-scale point is defined as level

1/2 LSB beyond the last code transition. The deviation is measured from the center of each particular code to

the true straight line between these two points.

Differential Nonlinearity

An ideal ADC exhibits code transitions that are exactly 1 LSB apart. DNL is the deviation from this ideal value.

A differential nonlinearity error of less than ±1 LSB ensures no missing codes.

Zero Offset

The major carry transition should occur when the analog input is at zero volts. Zero error is defined as the

deviation of the actual transition from that point.

Gain Error

The first code transition should occur at an analog value 1/2 LSB above negative full scale. The last transition

should occur at an analog value 1 1/2 LSB below the nominal full scale. Gain error is the deviation of the actual

difference between first and last code transitions and the ideal difference between first and last code transitions.

Signal-to-noise Ratio + Distortion (SINAD)

SINAD is the ratio of the rms value of the measured input signal to the rms sum of all other spectral components

below the Nyquist frequency, including harmonics but excluding dc. The value for SINAD is expressed in

decibels.

Effective Number of Bits (ENOB)

For a sine wave, SINAD can be expressed in terms of the number of bits. Using the following formula,

N +

(SINAD * 1.76)

6.02

it is possible to get a measure of performance expressed as N, the effective number of bits. Thus, the effective

number of bits for a device for sine wave inputs at a given input frequency can be calculated directly from its

measured SINAD.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of the first six harmonic components to the rms value of the measured input

signal and is expressed as a percentage or in decibels.

Spurious Free Dynamic Range (SFDR)

SFDR is the difference in dB between the rms amplitude of the input signal and the peak spurious signal.