Datasheet

2
f1
2
f10
2
f2
10
‡
A
A++A
logTHD = 20
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ADC128S102
SNAS298F –AUGUST 2005–REVISED MAY 2013 www.ti.com
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
specification 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.
FULL SCALE ERROR (FSE) is a measure of how far the last code transition is from the ideal 1½ LSB below
V
REF
+
and is defined as:
V
FSE
= V
max
+ 1.5 LSB – V
REF
+
(1)
where V
max
is the voltage at which the transition to the maximum code occurs. FSE can be expressed in Volts,
LSB or percent of full scale range.
GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (V
REF
- 1.5
LSB), 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 (½ LSB below the first code transition) through positive 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 both the second or the third order intermodulation products to the power in one of the original
frequencies. Second order products are f
a
± f
b
, where f
a
and f
b
are the two sine wave input frequencies. Third
order products are (2f
a
± f
b
) and (f
a
± 2f
b
). IMD is usually expressed in dB.
MISSING CODES are those output codes that will never appear at the ADC outputs. These codes cannot be
reached with any input value. The ADC128S102 is ensured 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).
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 d.c. or
the harmonics included in THD.
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 components below half the clock frequency, including
harmonics but excluding d.c.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, 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, expressed in 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 calculated
as:
(2)
where A
f1
is the RMS power of the input frequency at the output and A
f2
through A
f10
are the RMS power in the
first 9 harmonic frequencies.
THROUGHPUT TIME is the minimum time required between the start of two successive conversions. It is the
acquisition time plus the conversion and read out times. In the case of the ADC128S102, this is 16 SCLK
periods.
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