
Part Name  Description  Manufacturer 
ADC081S021CISDX  Single Channel, 50 to 200 ksps, 8Bit A/D Converter  National >Texas Instruments 
ADC081S021CISDX Datasheet PDF : 17 Pages

Specification Definitions
ACQUISITION TIME is the time required to acquire the input
voltage. That is, it is time required for the hold capacitor to
charge up to the input voltage.
APERTURE DELAY is the time between the fourth falling
SCLK edge of a conversion and the time 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.
CONVERSION TIME is the time required, after the input
voltage is acquired, for the ADC to convert the input voltage
to a digital word.
DIFFERENTIAL NONLINEARITY (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 SignaltoNoise and
Distortion or SINAD. ENOB is defined as
(SINAD − 1.76) / 6.02 and says that the converter is equiva
lent 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 (VREF − 1 LSB), after
adjusting for offset error.
INTEGRAL NONLINEARITY (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 second and third
order intermodulation products to the sum of the power in
both of the original frequencies. IMD is usually expressed in
dB.
MISSING CODES are those output codes that will never
appear at the ADC outputs. The ADC081S021 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 + 1 LSB).
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 onehalf the
sampling frequency, not including harmonics or d.c.
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 d.c.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ
ence, expressed in dB, between the desired signal ampli
tude to the amplitude of the peak spurious spectral compo
nent, where a spurious spectral component is any signal
present in the output spectrum that is not present at the input
and may or may not be a harmonic.
TOTAL HARMONIC DISTORTION (THD) is the ratio, ex
pressed in dB or dBc, of the rms total of the first five
harmonic components at the output to the rms level of the
input signal frequency as seen at the output. THD is calcu
lated as
where Af1 is the RMS power of the input frequency at the
output and Af2 through Af6 are the RMS power in the first 5
harmonic frequencies.
THROUGHPUT TIME is the minimum time required between
the start of two successive conversion. It is the acquisition
time plus the conversion time.
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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