Definitions

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values

on an actual transfer function from a straight line. This

straight line can be either a best-straight-line fit or a line

drawn between the end points of the transfer function,

once offset and gain errors have been nullified. The

static linearity parameters for the MAX1177 are mea-

sured using the end-point method.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between

an actual step width and the ideal value of 1 LSB. A

DNL error specification of 1 LSB guarantees no missing

codes and a monotonic transfer function.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital

samples, signal-to-noise ratio (SNR) is the ratio of the

full-scale analog input (RMS value) to the RMS quanti-

zation error (residual error). The ideal, theoretical mini-

mum analog-to-digital noise is caused by quantization

noise error only and results directly from the ADC’s res-

olution (N bits):

where N = 16 bits.

In reality, there are other noise sources besides quanti-

zation noise: thermal noise, reference noise, clock jitter,

etc. The SNR is computed by taking the ratio of the

RMS signal to the RMS noise, which includes all spec-

tral components minus the fundamental, the first five

harmonics, and the DC offset.

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the

fundamental input frequency’s RMS amplitude to the

RMS equivalent of all the other ADC output signals:

Effective Number of Bits

Effective number of bits (ENOB) indicates the global

accuracy of an ADC at a specific input frequency and

sampling rate. An ideal ADC error consists of quantiza-

tion noise only. With an input range equal to the full-

scale range of the ADC, calculate the ENOB as follows:

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the RMS

sum of the first five harmonics of the input signal to the

fundamental itself. This is expressed as:

Spurious-Free Dynamic Range

Spurious-free dynamic range (SFDR) is the ratio of the

RMS amplitude of the fundamental (maximum signal

component) to the RMS value of the next-largest fre-

quency component.

THD

VVV

V

V

=×

++

+





















20

2

2

3

2

4

2

5

2

1

log

ENOB

SINAD

=

−176

602

.

.

SINAD dB

Signal

Noise Distortion

RMS

RMS

(

)

log

()

=×

+













20

SNR

N

dB

=× +

(.

.

)

602

1 76

16-Bit, 135ksps, Single-Supply ADC

with 0 to 10V Input Range

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