Datasheet

ADC108S022
www.ti.com SNAS338F –SEPTEMBER 2005–REVISED MARCH 2013
Specification Definitions
ACQUISITION TIME is the time required for the ADC to acquire the input voltage. During this time, the hold
capacitor is charged by the input voltage.
APERTURE DELAY is the time between the fourth falling edge of SCLK and the time when the input signal is
internally acquired or held for conversion.
CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input
voltage to a digital word.
CHANNEL-TO-CHANNEL ISOLATION is resistance to coupling of energy from one channel into another
channel.
CROSSTALK is the coupling of energy from one channel into another channel. This is similar to Channel-to-
Channel Isolation, except for the sign of the data.
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
+
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 (1)
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 ADC108S022 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
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 components below half the clock frequency,
including harmonics but excluding d.c.
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