Data Conversion Definition of Terms

DNL  

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. DNL is commonly measured at the rated clock frequency with a ramp input.

INL 

INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from zero scale or negative full scale (1/2 LSB below the first code transition) through positive full scale (1/2 LSB above the last code transition). The deviation of any given code from this straight line is measured from the center of that code value. The end point test method is used. INL is commonly measured at rated clock frequency with a ramp input.

GAIN ERROR 

Gain Error (Full Scale Error) is the difference between the input voltage just causing a transition to positive full scale and VREF - 1.5 LSB.

OFFSET ERROR 

Offset Error is the difference between the ideal LSB transition to the actual transition point.

SNR

(Signal to Noise Ratio) is the ratio, expressed in decibels, of the RMS value of the input signal to the RMS value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or DC.

THD 

(TOTAL HARMONIC DISTORTION ) is the ratio, expressed in dB or dBc, of the rms total of the first six harmonic components to the RMS value of the input signal at the output.

When comparing A/D converters from different manufacturers, check the number of harmonics they use for their THD calculations. An A/D converter that is specified with too small a number of harmonics (usually less than 5 or 6) may list an artificially optimistic value for THD in the datasheet. Excessive THD in communications applications can result in the generation of additional signals that can interfere with other communications channels.

SINAD 

(SIgnal-to-Noise And Distortion) is the ratio, expressed in decibels, of the RMS value of the input signal present at the output to the RMS value of all other spectral components in the output that are below half the sample rate, including harmonics but excluding DC.

SFDR 

SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input signal at the output and the peak spurious signal. where a spurious signal is any signal present in the output spectrum that is not present at the input.

ENOB

(Estimated Number Of Bits) indicates the resolution that an ideal A/D converter would have if that ideal A/D converter had the SINAD of the real A/D converter being considered. That is, an A/D converter that has an ENOB of 7.0 has the same SINAD as a perfect A/D converter with 7.0 bits of resolution.

To access more definitions look at the A/D Converter Definition of Terms document (in PDF format).

To learn more details about choosing the right A/D converter, see the Electronic Products article Selecting high-speed A/D converters (on the Electronic Products web site) written by Nicholas Gray.