4

Terminology

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the

ADC.

Integral Nonlinearity (INL)

INL is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function.

Offset error

Offset error is the deviation of the center scale code from the ideal scale code corresponding to 0 V differential

input voltage.

Gain error

The gain is the derivative of the digital output code vs. the input signal. Graphically, for the output code vs. input

signal transfer function (an ideal straight line), the gain is the slope of such function. The gain error is the %

difference between the measured slope and the expected one.

Signal-to-Noise-and-Distortion Ratio (SINAD or SNDR)

SINAD is the measured ratio of signal to noise and distortion at the output of the ADC. The signal is the RMS

value of the sine wave, and noise is the RMS sum of all non-fundamental AC signals up to half the sampling

frequency (fS / 2), including harmonics.

Signal-to-Noise Ratio (SNR)

SNR is the measured ratio of signal to noise at the output of the ADC. The signal is the RMS amplitude of the

fundamental. Noise is the RSM sum of all non-fundamental AC signals up to half the sampling frequency (fS/2).

The ratio is dependent on the number of quantization levels in the conversion: the greater the number of levels,

the smaller the quantization noise. The theoretical signal-to-noise ratio for an ideal N-bit converter with a sine

wave input is given by

Signal-to-Noise Ratio = (6.02N + 1.76) [dB]

Therefore, for a 12-bit converter, the SNR is 74 dB.

Isolation transient immunity

The isolation transient immunity specifies the rise and fall speed of a transient pulse applied across the isolation

barrier, beyond which clock or data is corrupted.

Total Harmonic Distortion (THD)

THD is the ratio of the RMS sum of harmonics to the fundamental. The THD stated in this datasheet is defined as:

THD=20log V22+V32+V42+V52+V62

V1

where: V1 is the RMS amplitude of the fundamental. V2, V3, V4, V5, and V6 are the RMS amplitudes of the second

through the sixth harmonics. The result is in dB.

Spurious Free Dynamic Range (SFDR)

SFDR is defined as the ratio of the RMS value of the AC Noise Peak (up to fS / 2) to the RMS value of the

fundamental.

Effective Number of Bits (ENOB)

ENOB is defined by:

ENOB = (SINAD - 1.76) / 6.02 [bits]

Noise free code resolution

Noise free code resolution represents the resolution in bits for which there is no code flicker. The noise free code

resolution for an N-bit converter is defined as

Noisefreecoderesolution= log2 2 N 

Peak−to−Peak Noise bits

The peak-to-peak noise in LSBs is measured with VIN+ = VIN− = 0 V.

Common-Mode Rejection Ratio (CMRR)

CMRR is defined as the ratio of the power in the ADC output with an input differential sine wave, PD, to the power

of an input peak-to-peak sine wave applied to the common-mode voltage of VIN+ and VIN−, PCM, as:

ISOSD61

Terminology

DS13605 - Rev 11

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