ADC101S101EVAL datasheet(10/23 Pages) NSC

10 / 23 page

Specification Definitions

APERTURE DELAY is the time after the falling edge of CS

to when the input signal is acquired or held for conversion.

APERTURE JITTER (APERTURE UNCERTAINTY) is the

variation in aperture delay from sample to sample. Aperture

jitter manifests itself as noise in the output.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of

the maximum deviation from the ideal step size of 1 LSB.

DUTY CYCLE is the ratio of the time that a repetitive digital

waveform is high to the total time of one period. The speci-

fication here refers to the SCLK.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE

BITS) is another method of specifying Signal-to-Noise and

Distortion or SINAD. ENOB is defined as (SINAD - 1.76) /

6.02 and says that the converter is equivalent to a perfect

ADC of this (ENOB) number of bits.

FULL POWER BANDWIDTH is a measure of the frequency

at which the reconstructed output fundamental drops 3 dB

below its low frequency value for a full scale input.

GAIN ERROR is the deviation of the last code transition

(111...110) to (111...111) from the ideal (V

REF - 1.5 LSB for

ADC121S101 and ADC101S101, V

REF

- 1 LSB for

ADC081S101), after adjusting for offset error.

INTEGRAL NON-LINEARITY (INL) is a measure of the

deviation of each individual code from a line drawn from

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.

INTERMODULATION DISTORTION (IMD) is the creation of

additional spectral components as a result of two sinusoidal

frequencies being applied to the ADC input at the same time.

It is defined as the ratio of the power in the either the two

second order or all four third order intermodulation products

to the sum of the power in both of the original frequencies.

IMD is usually expressed in dBFS.

MISSING CODES are those output codes that will never

appear at the ADC outputs. The ADC121S101/101S101/

081S101 is guaranteed not to have any missing codes.

OFFSET ERROR is the deviation of the first code transition

(000...000) to (000...001) from the ideal (i.e. GND + 0.5 LSB

for the ADC121S101 and ADC101S101, and GND+1LSB

for the ADC081S101).

SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in

dB, 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.

SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD)

Is the ratio, expressed in dB, of the rms value of the input

signal to the rms value of all of the other spectral compo-

nents below half the clock frequency, including harmonics

but excluding dc.

SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-

ence, expressed in dB, between the rms values of the input

signal and the peak spurious signal, where a spurious signal

is any signal present in the output spectrum that is not

present at the input.

TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-

pressed in dBc, of the rms total of the first five harmonic

levels at the output to the level of the fundamental at the

output. THD is calculated as

where Af

1 is the RMS power of the fundamental (output)

frequency and Af

2 through Af6 are the RMS power in the first

5 harmonic frequencies.

TOTAL UNADJUSTED ERROR is the worst deviation found

from the ideal transfer function. As such, it is a comprehen-

sive specification which includes full scale error, linearity

error, and offset error.

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