AD7266_15 Datasheet, PDF (12/29 Pages) Analog Devices – Differential/Single-Ended Input, Dual 2 MSPS, 12-Bit, 3-Channel SAR ADC

TERMINOLOGY
Differential Nonlinearity (DNL)
Differential nonlinearity is the difference between the measured
and the ideal 1 LSB change between any two adjacent codes in
the ADC.
Integral Nonlinearity (INL)
Integral nonlinearity 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
with a single (1) LSB point below the first code transition, and
full scale with a 1 LSB point above the last code transition.
Offset Error
Offset error applies to straight binary output coding. It is the
deviation of the first code transition (00 . . . 000) to (00 . . . 001)
from the ideal (AGND + 1 LSB).
Offset Error Match
Offset error match is the difference in offset error across all
12 channels.
Gain Error
Gain error applies to straight binary output coding. It is the
deviation of the last code transition (111 . . . 110) to (111 . . .
111) from the ideal (VREF − 1 LSB) after the offset error is
adjusted out. Gain error does not include reference error.
Gain Error Match
Gain error match is the difference in gain error across all
12 channels.
Zero Code Error
Zero code error applies when using twos complement output
coding with, for example, the 2 × VREF input range as −VREF to
+VREF biased about the VREF point. It is the deviation of the
midscale transition (all 1s to all 0s) from the ideal VIN voltage
(VREF).
Zero Code Error Match
Zero code error match refers to the difference in zero code error
across all 12 channels.
Positive Gain Error
This applies when using twos complement output coding with,
for example, the 2 × VREF input range as −VREF to +VREF biased
about the VREF point. It is the deviation of the last code
transition (011…110) to (011…111) from the ideal (+VREF −
1 LSB) after the zero code error is adjusted out.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode after the
end of 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 ±1/2 LSB, after the end of conversion.
AD7266
Signal-to-(Noise + Distortion) Ratio
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 non-fundamental signals
up to half the sampling frequency (fS/2), excluding dc. The ratio
is dependent on the number of quantization levels in the
digitization 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
Therefore, for a 12-bit converter, this is 74 dB.
Total Harmonic Distortion (THD)
Total harmonic distortion is the ratio of the rms sum of
harmonics to the fundamental. For the AD7266, it is defined as
THD(dB) = 20 log ^{V22 + V32 + V42 + V52 + V62}
V₁
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, V5, and V6 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 fS/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, but 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
crosstalk between channels. It is measured by applying a full-
scale (2 × VREF when VDD = 5 V, VREF when VDD = 3 V), 10 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 (0 V to VREF). The result obtained
is the worst-case across all 12 channels for the AD7266.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities create distortion
products at sum, and difference 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 are 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).
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