AD7366/AD7367
Rev. D | Page 14 of 28
TERMINOLOGY
Differential Nonlinearity (DNL)
DNL is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Integral Nonlinearity (INL)
INL is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The
endpoints of the transfer function are zero scale, a point 1 LSB
below the first code transition, and full scale, a point 1 LSB above
the last code transition.
Zero Code Error
The deviation of the midscale transition (all 1s to all 0s) from
the ideal V
IN
voltage, that is, AGND − ½ LSB for bipolar ranges
and 2 × V
REF
− 1 LSB for the unipolar range.
Positive Full-Scale Error
The deviation of the last code transition (011…110) to (011…111)
from the ideal (that is, +4 × V
REF
− 1 LSB or +2 × V
REF
– 1 LSB)
after the zero code error has been factored out.
Negative Full-Scale Error
The deviation of the first code transition (10…000) to (10…001)
from the ideal (that is, −4 × V
REF
+ 1 LSB, −2 × V
REF
+ 1 LSB, or
AGND + 1 LSB) after the zero code error has been factored out.
Zero Code Error Match
The difference in zero code error across all channels.
Positive Full-Scale Error Match
The difference in positive full-scale error across all channels.
Negative Full-Scale Error Match
The difference in negative full-scale error across all channels.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of a conversion. Track-and-hold acquisition time is the time
required for the output of the track-and-hold amplifier to reach
its final value, within ±½ LSB, after the end of a conversion.
Signal-to-Noise (+ Distortion) Ratio (SINAD)
This ratio is the measured ratio of signal-to-noise (+ distortion)
at the output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals up
to half the sampling frequency (f
S
/2), excluding dc. The ratio is
dependent on the number of quantization levels in the digitiza-
tion process: the more levels, the smaller the quantization noise.
The theoretical signal-to-noise (+ distortion) ratio for an ideal
N-bit converter with a sine wave input is as follows:
Signal-to-Noise (+ Distortion) = (6.02N + 1.76) dB
Thus, for a 12-bit converter, the SINAD is 74 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the fundamental.
For the AD7366/AD7367, THD is defined as follows:
1
65432
V
VVVVV
THD
22222
log20)dB(
++++
=
where:
V
1
is the rms amplitude of the fundamental.
V
2
, V
3
, V
4
, V
5
, and V
6
are the rms amplitudes of the second
through the sixth harmonics.
Peak Harmonic or Spurious Noise
Peak harmonic, or spurious noise, is the ratio of the rms value
of the next largest component in the ADC output spectrum
(up to f
S
/2, excluding dc) to the rms value of the fundamental.
Normally, the value of this specification is determined by the
largest harmonic in the spectrum. However, for ADCs where
the harmonics are buried in the noise floor, it is a noise peak.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of the level of cross-
talk between any two channels when operating in any of the
input ranges. It is measured by applying a full-scale, 150 kHz
sine wave signal to all unselected input channels and determining
how much that signal is attenuated in the selected channel with
a 50 kHz signal. The figure given is the typical value across all
four channels for the AD7366/AD7367 (see Figure 9 for more
information).
Intermodulation Distortion (IMD)
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion prod-
ucts at the sum, and different frequencies of mfa ± nfb, where
m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms
are those for which neither m nor n is equal to zero. For example,
the second-order terms include (fa + fb) and (fa − fb), and the
third-order terms include (2fa + fb), (2fa − fb), (fa + 2fb), and
(fa − 2fb).
The AD7366/AD7367 are tested using the CCIF standard where
two input frequencies near the top end of the input bandwidth
are used. In this case, the second-order terms are usually distanced
in frequency from the original sine waves, and the third-order
terms are usually at a frequency close to the input frequencies.
As a result, the second- and third-order terms are specified
separately. The calculation of the intermodulation distortion is
as per the THD specification, where it is the ratio of the rms
sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in decibels.
