ADC121C021CIMKX NSC [National Semiconductor], ADC121C021CIMKX Datasheet - Page 10

• Manufacturer Part Number: ADC121C021CIMKX
• Description: I2C-Compatible, 12-Bit Analog-to-Digital Converter (ADC) with Alert Function
• Manufacturer: NSC [National Semiconductor]

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Specification Definitions
ACQUISITION TIME is the time required for the ADC to ac-
quire the input voltage. During this time, the hold capacitor is
charged by the input voltage.
APERTURE DELAY is the time between the start of a con-
version and the time when the input signal is internally ac-
quired or held for conversion.
CONVERSION TIME is the time required, after the input volt-
age is acquired, for the ADC to convert the input voltage to a
digital word.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
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
adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the de-
viation of each individual code from a line drawn from negative
full scale (½ LSB below the first code transition) through pos-
itive full scale (½ 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 an individual ADC input at the
same time. It is defined as the ratio of the power in either the
second or the third order intermodulation products to the sum
of the power in both of the original frequencies. Second order
products are f
input frequencies. Third order products are (2f
(f
MISSING CODES are those output codes that will never ap-
pear at the ADC output. The ADC121C021 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).
a
± 2f
b
). IMD is usually expressed in dB.
a
± f
b
, where f
a
and f
b
are the two sine wave
REF
- 1.5 LSB), after
a
± f
b
) and
10
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 sam-
pling 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 com-
ponents 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 amplitude
to the amplitude of the peak spurious spectral component,
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 dBc, of the rms total of the first n harmonic com-
ponents at the output to the rms level of the input signal
frequency as seen at the output. THD is calculated as
where A
put and A
harmonic frequencies.
THROUGHPUT TIME is the minimum time required between
the start of two successive conversions. It is the acquisition
time plus the conversion time.
LEAST SIGNIFICANT BIT (LSB) is the bit that has the small-
est value or weight of all bits in a word. This value is
where V
resolution in bits, which is 12 for the ADC121C021.
MOST SIGNIFICANT BIT (MSB) is the bit that has the largest
value or weight of all bits in a word. Its value is 1/2 of V
f1
A
is the supply voltage for this product, and "n" is the
is the RMS power of the input frequency at the out-
f2
through A
fn
LSB = V
are the RMS power in the first n
A
/ 2
n
A
.