Datasheet AD9224 (Analog Devices) - 5

AD9224
DEFINITIONS OF SPECIFICATION
INTEGRAL NONLINEARITY (INL) APERTURE JITTER Aperture jitter is the variation in aperture delay for successive
samples and is manifested as noise on the input to the A/D. INL refers to the deviation of each individual code from a line
drawn from “negative full scale” through “positive full scale.”
The point used as “negative full scale” occurs 1/2 LSB before
the first code transition. “Positive full scale” is defined as a level
1 1/2 LSB beyond the last code transition. The deviation is
measured from the middle of each particular code to the true
straight line. APERTURE DELAY Aperture delay is a measure of the sample-and-hold amplifier
(SHA) performance and is measured from the rising edge of the
clock input to when the input signal is held for conversion.
SIGNAL-TO-NOISE AND DISTORTION (S/N+D, SINAD)
RATIO DIFFERENTIAL NONLINEARITY (DNL, NO MISSING
CODES) S/N+D is the ratio of the rms value of the measured input signal
to the rms sum of all other spectral components below the
Nyquist frequency, including harmonics but excluding dc. The
value for S/N+D is expressed in decibels. An ideal ADC exhibits code transitions that are exactly 1 LSB
apart. DNL is the deviation from this ideal value. Guaranteed
no missing codes to 12-bit resolution indicates that all 4096
codes, respectively, must be present over all operating ranges. EFFECTIVE NUMBER OF BITS (ENOB) For a sine wave, SINAD can be expressed in terms of the number of bits. Using the following formula, ZERO ERROR The major carry transition should occur for an analog value
1/2 LSB below VINA = VINB. Zero error is defined as the
deviation of the actual transition from that point. N = (SINAD – 1.76)/6.02
it is possible to get a measure of performance expressed as N,
the effective number of bits. GAIN ERROR The first code transition should occur at an analog value
1/2 LSB above negative full scale. The last transition should
occur at an analog value 1 1/2 LSB below the nominal full scale.
Gain error is the deviation of the actual difference between first
and last code transitions and the ideal difference between first
and last code transitions. Thus, effective number of bits for a device for sine wave inputs
at a given input frequency can be calculated directly from its
measured SINAD.
TOTAL HARMONIC DISTORTION (THD) THD is the ratio of the rms sum of the first six harmonic components to the rms value of the measured input signal and is
expressed as a percentage or in decibels. TEMPERATURE DRIFT The temperature drift for zero error and gain error specifies the
maximum change from the initial (+25°C) value to the value at
TMIN or TMAX. SIGNAL-TO-NOISE RATIO (SNR) SNR is the ratio of the rms value of the measured input signal to
the rms sum of all other spectral components below the Nyquist
frequency, excluding the first six harmonics and dc. The value
for SNR is expressed in decibels. POWER SUPPLY REJECTION The specification shows the maximum change in full scale from
the value with the supply at the minimum limit to the value with
the supply at its maximum limit. SPURIOUS FREE DYNAMIC RANGE (SFDR) SFDR is the difference in dB between the rms amplitude of the
input signal and the peak spurious signal. REV. A –5–