AD7366-5/AD7367-5
Rev. B | 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 single (1)
LSB point below the first code transition and full scale, a point
1 LSB above the last code transition.
Zero Code Error
This is 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
This is 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 adjusted out.
Negative Full-Scale Error
This is 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
adjusted out.
Zero Code Error Match
This is the difference in zero code error across all 12 channels.
Positive Full-Scale Error Match
This is the difference in positive full-scale error across all channels.
Negative Full-Scale Error Match
This is 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 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 given by:
Signal-to-Noise (+ Distortion) = (6.02N + 1.76) dB
Thus, for a 12-bit converter, this is 74 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the
fundamental. For the AD7366-5/AD7367-5, it is defined as:
1
2
6
2
5
2
4
2
3
2
2
log20(dB)
V
VVVVV
THD
++++
=
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 defined as 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 deter-
mined 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 determin-
ing how much that signal is attenuated in the selected channel
with a 50 kHz signal. The figure given is the typical across all
four channels for the AD7366-5/AD7367-5 (see the Figure 9 for
more information).
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa
and fb, any active device with nonlinearities creates distortion
products 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), while the third-order terms include (2fa + fb),
(2fa − fb), (fa + 2fb), and (fa − 2fb).
The AD7366-5/AD7367-5 is 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,
while 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 intermodula-
tion 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.
