AD1672
REV. 0
–6–
DEFINITIONS OF SPECIFICATIONS
INTEGRAL NONLINEARITY ERROR (INL)
Integral nonlinearity error 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 (all zeros to only
the LSB on). “Positive full scale” is defined as a level 1 1/2 LSB
beyond the last code transition (to all ones). The deviation is
measured from the middle of each particular code to the true
straight line.
DIFFERENTIAL LINEARITY ERROR (DNL, NO MISSING
CODES)
An ideal ADC exhibits code transitions that are exactly 1 LSB
apart. DNL is the deviation from this ideal value. Thus every
code must have a finite width. Guaranteed no missing codes to
12-bit resolution indicates that all 4096 codes must be present
over all operating ranges.
UNIPOLAR OFFSET ERROR
In the unipolar mode, the first transition should occur at a level
1/2 LSB above analog common. Unipolar offset is defines as
the deviation of the actual from that point.
BIPOLAR ZERO ERROR
In the bipolar mode, the major carry transition should occur for
an analog value 1/2 LSB below analog common. Zero error is
defined as the deviation of the actual transition from that point.
GAIN ERROR
The first transition should occur for an analog value 1/2 LSB
above nominal negative full scale. The last transition should
occur for 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.
POWER SUPPLY REJECTION
One of the effects of power supply error on the performance of
the device will be a small change in gain. The specifications
show the maximum change in the converter’s full scale as the
supplies are varied from minimum to maximum values.
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.
CODE TRANSITION NOISE
The effects of noise are to introduce an uncertainty in the precise determination of the analog input values at which the output code transitions take place, and, in effect, to increase or
reduce the quantization band. Code transition noise describes
the quantization band variation resulting from noise in terms of
rms LSBs.
APERTURE DELAY
Aperture delay is a measure of the Sample-and-Hold (SHA)
performance and is measured from the rising edge of the clock
input to when the input signal is held for conversion.
OVERVOLTAGE RECOVERY TIME
Overvoltage recovery time is defined as that amount of time
required for the ADC to achieve a specified accuracy after an
overvoltage (50% greater than full-scale range), measured from
the time the overvoltage signal reenters the converter’s range.
DYNAMIC SPECIFICATIONS
SIGNAL-TO-NOISE AND DISTORTION (S/N+D) RATIO
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.
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.
INTERMODULATION DISTORTION (IMD)
With inputs consisting of sine waves at two frequencies, fa and
fb, any device with nonlinearities will create distortion products,
of order (m + n), at sum and difference frequencies of
mfa ± nfb, where m, n = 0, 1, 2, 3. . . . Intermodulation terms
are those for which m or n is not equal to zero. For example,
the second order terms are (fa + fb) and (fa – fb) and the third
order terms are (2 fa + fb), (2 fa – fb), (fa + 2fb) and (2 fb – fa).
The IMD products are expressed as the decibel ratio of the rms
sum of the measured input signals to the rms sum of the distortion terms. The two signals are of equal amplitude and the peak
value of their sums is –0.5 dB from full-scale. The IMD products are normalized to a 0 dB input signal.
FULL-POWER BANDWIDTH
The full-power bandwidth is that input frequency at which the
amplitude of the reconstructed fundamental is reduced by 3 dB
for a full-scale input.
SPURIOUS FREE DYNAMIC RANGE
The difference, in dB, between the rms amplitude of the input
signal and the peak spurious signal.