AD1671
DEFINITIONS OF SPECIFICATIONS
INTEGRAL NONLINEARITY (INL)
DYNAMIC SPECIFICATIONS
SIGNAL-TO-NOISE PLUS 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, including har-
monics but excluding dc. The value for S/N+D is expressed in
decibels.
Integral nonlinearity refers to the deviation of each individual
code from a line drawn from “zero” through “full scale.” The
point used as “zero” occurs 1/2 LSB (1.22 mV for a 10 V span)
before the first code transition (all zeros to only the LSB on).
“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 low
side transition of each particular code to the true straight line.
EFFECTIVE NUMBER OF BITS (ENOB)
ENOB is calculated from the expression (S/N+D) = 6.02N +
1.76 dB, where N is equal to the effective number of bits.
DIFFERENTIAL LINEARITY ERROR (NO MISSING
CODES)
TOTAL HARMONIC DISTORTION (THD)
An ideal ADC exhibits code transitions that are exactly 1 LSB
apart. DNL is the deviation from the ideal value. Thus every
code has a finite width. Guaranteed no missing codes to 11- or
12-bit resolution indicates that all 2048 and 4096 codes, respec-
tively, must be present over all operating ranges. No missing
codes to 11 bits (in the case of a 12-bit resolution ADC) also
means that no two consecutive codes are missing.
THD is the ratio of the rms sum of the first six harmonic com-
ponents to the rms value of the measured input signal and is ex-
pressed 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 or-
der terms are (2 fa + fb), (2 fa – fb), (fa + 2 fb) and (2fb – 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 distor-
tion terms. The two signals are of equal amplitude and the peak
value of their sum is –0.5 dB from full scale. The IMD products
are normalized to a 0 dB input signal.
UNIPOLAR OFFSET
The first transition should occur at a level 1/2 LSB above analog
common. Unipolar offset is defined as the deviation of the ac-
tual from that point. This offset can be adjusted as discussed
later. The unipolar offset temperature coefficient specifies the
maximum change of the transition point over temperature, with
or without external adjustments.
BIPOLAR ZERO
In the bipolar mode the major carry transition (0111 11111111 to
1000 0000 0000) should occur for an analog value 1/2 LSB be-
low analog common. The bipolar offset error and temperature
coefficient specify the initial deviation and maximum change in
the error over temperature.
PEAK SPURIOUS OR PEAK HARMONIC COMPONENT
The peak spurious or peak harmonic component is the largest
spectral component, excluding the input signal and dc. This
value is expressed in decibels relative to the rms value of a full-
scale input signal.
GAIN ERROR
The last transition (from 1111 1111 1110 to 1111 1111 1111)
should occur for an analog value 1 1/2 LSB below the nominal
full scale (4.9963 volts for 5.000 volts full scale). The gain error
is the deviation of the actual level at the last transition from the
ideal level. The gain error can be adjusted to zero as shown in
Figures 4 through 7.
APERTURE DELAY
Aperture delay is the difference between thc switch delay and
the analog delay of the SHA. This delay represents the point in
time, relative to the rising edge of ENCODE input, that the
analog input is sampled.
APERTURE JITTER
Aperture jitter is the variation in aperture delay for successive
samples.
TEMPERATURE COEFFICIENTS
The temperature coefficients for unipolar offset, bipolar zero
and gain error specify the maximum change from the initial
(+25°C) value to the value at TMIN or TMAX
.
FULL POWER BANDWIDTH
The input frequency at which the amplitude of the recon-
structed fundamental is reduced by 3 dB for a full-scale input.
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 full-scale change from the initial value with
the supplies at the various limits.
–6–
REV. B
ADI [ ADI ]
